<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the WaMu Mortgage Pass-Through
Certificates, Series 2004-AR7, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-44

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


            WaMu Mortgage Pass-Through Certificates, Series 2004-AR8

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
WaMu Mortgage Pass-Through Certificates, Series 2004-AR8, issued pursuant to the
Pooling and Servicing Agreement dated as of June 1, 2004(the "Pooling
Agreement") and registered pursuant to a registration statement on Form S-3
(File No. 333-103345) (such mortgage pass-through certificates, the
"Certificates"), are incorporated by reference as set forth in Part IV, Item 15.
Capitalized terms used herein but not otherwise defined shall have the meanings
assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


WaMu Mortgage Pass-Through Certificates, Series
2004-AR8


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------


July 2004                                 July 30, 2004

July 2004
Revised Monthly Distribution Report       8-K/A filed August 17, 2004

August 2004                               August 27, 2004

September 2004                            September 29, 2004

October 2004                              October 27, 2004

November 2004                             November 30, 2004

December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:


1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this annual report, of WaMu Mortgage
Pass-Through Certificates, Series 2004-AR8;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




None


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the WaMu Mortgage Pass-Through
Certificates, Series 2004-AR8, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-42

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


             WaMu Mortgage Pass-Through Certificates, Series 2004-S3

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
WaMu Mortgage Pass-Through Certificates, Series 2004-S3, issued pursuant to the
Pooling and Servicing Agreement dated as of June 1, 2004(the "Pooling
Agreement") and registered pursuant to a registration statement on Form S-3
(File No. 333-103345) (such mortgage pass-through certificates, the
"Certificates"), are incorporated by reference as set forth in Part IV, Item 15.
Capitalized terms used herein but not otherwise defined shall have the meanings
assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


WaMu Mortgage Pass-Through Certificates, Series
2004-S3


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------

July 2004                                 July 30, 2004
August 2004                               August 27, 2004
September 2004                            September 29, 2004
October 2004                              October 27, 2004
November 2004                             November 30, 2004
December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this annual report, of WaMu Mortgage
Pass-Through Certificates, Series 2004-S3;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




None


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the WaMu Mortgage Pass-Through
Certificates, Series 2004-S3, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-41

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


            WaMu Mortgage Pass-Through Certificates, Series 2004-CB2

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
WaMu Mortgage Pass-Through Certificates, Series 2004-CB2, issued pursuant to the
Pooling and Servicing Agreement dated as of June 1, 2004(the "Pooling
Agreement") and registered pursuant to a registration statement on Form S-3
(File No. 333-103345) (such mortgage pass-through certificates, the
"Certificates"), are incorporated by reference as set forth in Part IV, Item 15.
Capitalized terms used herein but not otherwise defined shall have the meanings
assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


WaMu Mortgage Pass-Through Certificates, Series
2004-CB2


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------

July 2004                                 July 30, 2004
August 2004                               August 27, 2004
September 2004                            September 29, 2004
October 2004                              October 27, 2004
November 2004                             November 30, 2004
December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this annual report, of WaMu Mortgage
Pass-Through Certificates, Series 2004-CB2;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




None


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the WaMu Mortgage Pass-Through
Certificates, Series 2004-CB2, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-45

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


                   Washington Mutual MSC Mortgage Pass-Through
                          Certificates, Series 2004-RA2

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
Washington Mutual MSC Mortgage Pass-Through Certificates, Series 2004-RA2,
issued pursuant to the Pooling and Servicing Agreement dated as of June 1,
2004(the "Pooling Agreement") and registered pursuant to a registration
statement on Form S-3 (File No. 333-103345) (such mortgage pass-through
certificates, the "Certificates"), are incorporated by reference as set forth in
Part IV, Item 15. Capitalized terms used herein but not otherwise defined shall
have the meanings assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


Washington Mutual MSC Mortgage Pass-Through
Certificates, Series 2004-RA2


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------


July 2004                                 July 30, 2004
August 2004                               August 27, 2004
September 2004                            September 29, 2004
October 2004                              October 27, 2004
November 2004                             November 30, 2004
December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this
annual report, of Washington Mutual MSC Mortgage Pass-Through Certificates,
Series 2004-RA2;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




Cendant Mortgage Corporation, Central Mortgage
Company, Chase Home Finance, LLC, Citimortgage,
Inc., Countrywide Home Loans, Inc.,  Fifth Third
Bank, First Horizon Home Loans, GMAC Mortgage
Corporation, Golden National Mortgage Banking
Corp, J.P. Morgan Chase & Company, Litton Loan
Servicing LP, National City Mortgage, Novus
Financial, Select Portfolio Servicing, Inc.,
Suntrust Mortgage, Inc.


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the Washington Mutual MSC Mortgage
Pass-Through Certificates, Series 2004-RA2, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-46

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


            WaMu Mortgage Pass-Through Certificates, Series 2004-AR9

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
WaMu Mortgage Pass-Through Certificates, Series 2004-AR9, issued pursuant to the
Pooling and Servicing Agreement dated as of July 1, 2004(the "Pooling
Agreement") and registered pursuant to a registration statement on Form S-3
(File No. 333-103345) (such mortgage pass-through certificates, the
"Certificates"), are incorporated by reference as set forth in Part IV, Item 15.
Capitalized terms used herein but not otherwise defined shall have the meanings
assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


WaMu Mortgage Pass-Through Certificates, Series
2004-AR9


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------

August 2004                               August 27, 2004
September 2004                            September 29, 2004
October 2004                              October 27, 2004
November 2004                             November 30, 2004
December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this annual report, of WaMu Mortgage
Pass-Through Certificates, Series 2004-AR9;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




None


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the WaMu Mortgage Pass-Through
Certificates, Series 2004-AR9, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-47

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


           WaMu Mortgage Pass-Through Certificates, Series 2004-AR10

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
WaMu Mortgage Pass-Through Certificates, Series 2004-AR10, issued pursuant to
the Pooling and Servicing Agreement dated as of July 1, 2004(the "Pooling
Agreement") and registered pursuant to a registration statement on Form S-3
(File No. 333-103345) (such mortgage pass-through certificates, the
"Certificates"), are incorporated by reference as set forth in Part IV, Item 15.
Capitalized terms used herein but not otherwise defined shall have the meanings
assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


WaMu Mortgage Pass-Through Certificates, Series
2004-AR10


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------

August 2004                               August 27, 2004
September 2004                            September 29, 2004
October 2004                              October 27, 2004
November 2004                             November 30, 2004
December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this annual report, of WaMu Mortgage
Pass-Through Certificates, Series 2004-AR10;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




None


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the WaMu Mortgage Pass-Through
Certificates, Series 2004-AR10, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-48

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


                   Washington Mutual MSC Mortgage Pass-Through
                          Certificates, Series 2004-RA3

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
Washington Mutual MSC Mortgage Pass-Through Certificates, Series 2004-RA3,
issued pursuant to the Pooling and Servicing Agreement dated as of July 1,
2004(the "Pooling Agreement") and registered pursuant to a registration
statement on Form S-3 (File No. 333-103345) (such mortgage pass-through
certificates, the "Certificates"), are incorporated by reference as set forth in
Part IV, Item 15. Capitalized terms used herein but not otherwise defined shall
have the meanings assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


Washington Mutual MSC Mortgage Pass-Through
Certificates, Series 2004-RA3


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------


August 2004                               August 27, 2004
September 2004                            September 29, 2004
October 2004                              October 27, 2004
November 2004                             November 30, 2004
December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this
annual report, of Washington Mutual MSC Mortgage Pass-Through Certificates,
Series 2004-RA3;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




BA Mortgage, Inc., Cendant Mortgage Corporation,
Cenlar, Central Mortgage Company, Chase Home
Finance, LLC, Countrywide Home Loans, Inc.,
Dovenmuehle Mortgage, Inc., Downey Savings and
Loan Assoc, Fifth Third Bank, First Horizon Home
Loans, GMAC Mortgage Corporation, Litton Loan
Servicing LP, National City Mortgage, Novus
Financial, Suntrust Mortgage, Inc., Wells Fargo
Home Mortgage, Inc.


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the Washington Mutual MSC Mortgage
Pass-Through Certificates, Series 2004-RA3, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-49

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


            WaMu Mortgage Pass-Through Certificates, Series 2004-CB3

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
WaMu Mortgage Pass-Through Certificates, Series 2004-CB3, issued pursuant to the
Pooling and Servicing Agreement dated as of August 1, 2004(the "Pooling
Agreement") and registered pursuant to a registration statement on Form S-3
(File No. 333-103345) (such mortgage pass-through certificates, the
"Certificates"), are incorporated by reference as set forth in Part IV, Item 15.
Capitalized terms used herein but not otherwise defined shall have the meanings
assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


WaMu Mortgage Pass-Through Certificates, Series
2004-CB3


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------


September 2004                            September 29, 2004
October 2004                              October 27, 2004
November 2004                             November 30, 2004
December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this annual report, of WaMu Mortgage
Pass-Through Certificates, Series 2004-CB3;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




None


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the WaMu Mortgage Pass-Through
Certificates, Series 2004-CB3, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-50

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


           WaMu Mortgage Pass-Through Certificates, Series 2004-AR11

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
WaMu Mortgage Pass-Through Certificates, Series 2004-AR11, issued pursuant to
the Pooling and Servicing Agreement dated as of August 1, 2004(the "Pooling
Agreement") and registered pursuant to a registration statement on Form S-3
(File No. 333-103345) (such mortgage pass-through certificates, the
"Certificates"), are incorporated by reference as set forth in Part IV, Item 15.
Capitalized terms used herein but not otherwise defined shall have the meanings
assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


WaMu Mortgage Pass-Through Certificates, Series
2004-AR11


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------


September 2004                            September 29, 2004
October 2004                              October 27, 2004
November 2004                             November 30, 2004
December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this annual report, of WaMu Mortgage
Pass-Through Certificates, Series 2004-AR11;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




None


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the WaMu Mortgage Pass-Through
Certificates, Series 2004-AR11, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-51

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


           WaMu Mortgage Pass-Through Certificates, Series 2004-AR12

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
WaMu Mortgage Pass-Through Certificates, Series 2004-AR12, issued pursuant to
the Pooling and Servicing Agreement dated as of October 1, 2004(the "Pooling
Agreement") and registered pursuant to a registration statement on Form S-3
(File No. 333-103345) (such mortgage pass-through certificates, the
"Certificates"), are incorporated by reference as set forth in Part IV, Item 15.
Capitalized terms used herein but not otherwise defined shall have the meanings
assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


WaMu Mortgage Pass-Through Certificates, Series
2004-AR12


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------

November 2004                             November 30, 2004
December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification


                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this annual report, of WaMu Mortgage
Pass-Through Certificates, Series 2004-AR12;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




None


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the WaMu Mortgage Pass-Through
Certificates, Series 2004-AR12, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-52

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


            WaMu Mortgage Pass-Through Certificates, Series 2004-CB4

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
WaMu Mortgage Pass-Through Certificates, Series 2004-CB4, issued pursuant to the
Pooling and Servicing Agreement dated as of October 1, 2004(the "Pooling
Agreement") and registered pursuant to a registration statement on Form S-3
(File No. 333-103345) (such mortgage pass-through certificates, the
"Certificates"), are incorporated by reference as set forth in Part IV, Item 15.
Capitalized terms used herein but not otherwise defined shall have the meanings
assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


WaMu Mortgage Pass-Through Certificates, Series
2004-CB4


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------

November 2004                             November 30, 2004
December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this annual report, of WaMu Mortgage
Pass-Through Certificates, Series 2004-CB4;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




None


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the WaMu Mortgage Pass-Through
Certificates, Series 2004-CB4, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-53

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


                   Washington Mutual MSC Mortgage Pass-Through
                          Certificates, Series 2004-RA4

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
Washington Mutual MSC Mortgage Pass-Through Certificates, Series 2004-RA4,
issued pursuant to the Pooling and Servicing Agreement dated as of October 1,
2004(the "Pooling Agreement") and registered pursuant to a registration
statement on Form S-3 (File No. 333-103345) (such mortgage pass-through
certificates, the "Certificates"), are incorporated by reference as set forth in
Part IV, Item 15. Capitalized terms used herein but not otherwise defined shall
have the meanings assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


Washington Mutual MSC Mortgage Pass-Through
Certificates, Series 2004-RA4


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------

November 2004                             November 30, 2004
December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this
annual report, of Washington Mutual MSC Mortgage Pass-Through Certificates,
Series 2004-RA4;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




Cendant Mortgage Corporation, Chase Home Finance,
LLC, Fifth Third Bank, GMAC Mortgage Corporation,
Litton Loan Servicing LP, National City Mortgage,
Novus Financial


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the Washington Mutual MSC Mortgage
Pass-Through Certificates, Series 2004-RA4, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-54

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


           WaMu Mortgage Pass-Through Certificates, Series 2004-AR13

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
WaMu Mortgage Pass-Through Certificates, Series 2004-AR13, issued pursuant to
the Pooling and Servicing Agreement dated as of November 1, 2004(the "Pooling
Agreement") and registered pursuant to a registration statement on Form S-3
(File No. 333-103345) (such mortgage pass-through certificates, the
"Certificates"), are incorporated by reference as set forth in Part IV, Item 15.
Capitalized terms used herein but not otherwise defined shall have the meanings
assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


WaMu Mortgage Pass-Through Certificates, Series
2004-AR13


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------

December 2004                             December 29, 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this annual report, of WaMu Mortgage
Pass-Through Certificates, Series 2004-AR13;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:




None


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the WaMu Mortgage Pass-Through
Certificates, Series 2004-AR13, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>






                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    Form 10-K

[X]  Annual report pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934 for the fiscal year ended December 31, 2004

[    ] Transition report pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934

     for the transition period from       to


              Commission File Number 333-103345-55

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
             (Exact name of Registrant as specified in its charter)

             Delaware                            94-2528990
 (State or other jurisdiction of    (I.R.S. Employer Identification No.)
          incorporation

                           1201 THIRD AVENUE, WMT 1706
                            SEATTLE, WASHINGTON 98101
                                 (206) 377-8555
         (Address, including zip code, and telephone number, including area
                    code, of registrant's principal executive offices)


           WaMu Mortgage Pass-Through Certificates, Series 2004-AR14

     ---------------------------------------------------------------------
            (Title of each class of securities covered by this Form)

Securities registered pursuant to Section 12(b) of the Act: None
Securities registered pursuant to Section 12(g) of the Act: None

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ] (as such reporting
obligations are modified as set forth in J.P. Morgan Mortgage Pass-Through
Corporation, SEC No-Action Letter, March 31, 1989, in reliance upon which the
registrant is filing this modified report).

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ] Not applicable.

     State the aggregate market value of the voting and non-voting common equity
held by non-affiliates of the registrant: None.

     Indicate the number of shares outstanding of each of the registrant's
classes of common stock, as of the latest practicable date: Not applicable.

                       DOCUMENTS INCORPORATED BY REFERENCE

The registrant's Reports on Form 8-K concerning the registrant's
WaMu Mortgage Pass-Through Certificates, Series 2004-AR14, issued pursuant to
the Pooling and Servicing Agreement dated as of December 1, 2004(the "Pooling
Agreement") and registered pursuant to a registration statement on Form S-3
(File No. 333-103345) (such mortgage pass-through certificates, the
"Certificates"), are incorporated by reference as set forth in Part IV, Item 15.
Capitalized terms used herein but not otherwise defined shall have the meanings
assigned to them in the Pooling Agreement.



                                     Part I

Item 1. Business.

     Not applicable.

Item 2. Properties.

     Information regarding the mortgaged properties related to the Certificates
is furnished by reference to the Annual Statement of Compliance attached hereto
as Exhibit 99.1.

Item 3. Legal Proceedings.

     There are no material pending legal proceedings with respect to the assets
of the Trust involving the registrant or, to the best knowledge of the
registrant, the Trustee, any Custodian, any Servicer or the assets of the Trust,
other than ordinary routine litigation incidental to the Trustee's, any
Custodian's, any Servicer's or the registrant's duties under the Pooling
Agreement.

Item 4. Submission of Matters to a Vote of Security Holders.


Not applicable.



                                     Part II

Item 5. Market for Registrant's Common Equity and Related Stockholder Matters.

     (a) To the knowledge of the registrant, there exists no established public
trading market for the Certificates.

     (b) The Certificates are represented by one or more certificates registered
in the name of Cede & Co., as nominee of the Depository Trust Company ("DTC")
and are held in book-entry form only. The registrant considers Cede & Co. to be
the sole holder of record of the Certificates.

     (c) Not applicable.

Item 6. Selected Financial Data.

         Not applicable.

Item 7. Management's Discussion and Analysis of Financial Condition and Results
of Operations.

     Not applicable.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk.

     Not applicable.

Item 8. Financial Statements and Supplementary Data.

     Not applicable.

Item 9. Changes in and Disagreements with Accountants on Accounting and
Financial Disclosure.

         None.

                                    Part III


Item 10. Directors and Executive Officers of the Registrant.

     Not applicable.

Item 11. Executive Compensation.

     Not applicable.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

     Not applicable.

Item 13. Certain Relationships and Related Transactions.

     Not applicable.

Item 14. Principal Accountant Fees and Services.

     Not applicable.


                                     Part IV

Item 15. Exhibits and Financial Statement Schedules

(a) Documents filed as part of this report.

     1. Not applicable.

     2. Not applicable.

     3. Not applicable.

(b) Exhibits required by Item 601


Exhibit No.             Description

31                      Rule 13a-14(d) Certification

99.1                    Officer's Certificate regarding
                        Annual Statement of Compliance of
                        Washington Mutual Mortgage
                        Securities Corp., dated March 28,
                        2005

99.2                    Independent Accountants' Report on Management's
                        Assertion Concerning Compliance with Washington Mutual
                        Mortgage Securities Corp.'s Minimum Servicing Standards
                        as of and for the year ended December 31, 2004
                        (incorporated by reference to the designated exhibit
                        included in the registrant's Current Report on Form 8-K,
                        filed on March 28, 2005, (SEC File No. 333-103345))


     The registrant filed Current Reports on Form 8-K that described
distributions made to Certificateholders on the Distribution Date occurring in
the month preceding the month in which such Current Report on Form 8-K was filed
and also provided certain information regarding delinquent Mortgage Loans and
credit enhancements as of such Distribution Date. Such Current Reports on Form
8-K are incorporated by reference herein, as follows:


WaMu Mortgage Pass-Through Certificates, Series
2004-AR14


EVENT REPORTED
Monthly Distribution Report sent to
holders of the Certificates for           Date Distribution Report
payments made in:                         Filed on Form 8-K:
-----------------                         ------------------


No distribution reports filed in 2004



<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Dated:  March 29, 2005         WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                            By: /s/ Thomas G. Lehmann
                                -------------------------------------
                               Thomas G. Lehmann
                               First Vice President

<PAGE>

Exhibit 31       Rule 13a-14(d) Certification



                                  CERTIFICATION

I, Thomas G.  Lehmann,  a First Vice  President of  Washington  Mutual  Mortgage
Securities Corp., certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this annual report, of WaMu Mortgage
Pass-Through Certificates, Series 2004-AR14;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the trustee by the servicer under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;

4. I am responsible for reviewing the activities performed by the servicer under
the pooling and servicing, or similar, agreement and based upon my knowledge and
the annual compliance review required under that agreement, and except as
disclosed in the reports, the servicer has fulfilled its obligations under that
agreement; and

5. The reports disclose all significant deficiencies relating to the servicer's
compliance with the minimum servicing standards based upon the report provided
by an independent public accountant, after conducting a review in compliance
with the Uniform Single Attestation Program for Mortgage Bankers or similar
procedure, as set forth in the pooling and servicing, or similar, agreement,
that is included in these reports.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated third parties acting as servicers
and sub-servicers:


None


Dated: March 29, 2005

                                     /s/ Thomas G. Lehmann
                                     ----------------------------------------
                                     Thomas G. Lehmann
                                     First Vice President



<PAGE>



Exhibit 99.1        Officer's Certificate regarding Annual Statement of
                    Compliance of Washington Mutual Mortgage Securities Corp.

                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
                              OFFICER'S CERTIFICATE

The undersigned officer of Washington Mutual Mortgage Securities Corp., a
Delaware corporation (the "Company") hereby certifies on behalf of the Company
and on his own behalf for purposes of the WaMu Mortgage Pass-Through
Certificates, Series 2004-AR14, as follows:

1. I am a duly appointed and qualified First Vice President of the Company.

2. Capitalized terms used and not defined herein shall have the meanings
ascribed to such terms in the Pooling and Servicing Agreement related to the
above-referenced series of Certificates.

3. I am duly authorized to execute and deliver this Officer's Certificate on
behalf of the Company.

4. A review of the activities of the Master Servicer during the preceding
calendar year and performance under this Agreement has been made under my
supervision.

5. To the best of my knowledge, based on such review, the Master Servicer has
fulfilled all its obligations under the Agreement throughout such year.



     IN WITNESS WHEREOF, I have signed my name as of March 29, 2005.





                   WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.


                     By: /s/ Thomas G. Lehmann
                         -------------------------------------
                         Thomas G. Lehmann
                         First Vice President






<PAGE>