<PAGE>

                                                                   Exhibit 10.18

                                                                  EXECUTION COPY

                        AMENDMENT NO. 2 dated as of March 29, 2000 (this
                  "Amendment"), to the CREDIT AGREEMENT dated as of June 23,
                  1999, as amended by Amendment No. 1 dated as of January 13,
                  2000 (the "Credit Agreement"), among ANTEON CORPORATION, a
                  Virginia corporation (the "Borrower"), the Lenders (as defined
                  in Article I of the Credit Agreement), CREDIT SUISSE FIRST
                  BOSTON, a bank organized under the laws of Switzerland, acting
                  through its New York branch, as an Issuing Bank (as defined in
                  Article I of the Credit Agreement), and as administrative
                  agent (in such capacity, the "Administrative Agent") for the
                  Lenders, MELLON BANK, N.A., a national banking association, as
                  syndication agent (in such capacity, the "Syndication Agent"),
                  as swingline lender (in such capacity, the "Swingline
                  Lender"), and as collateral agent (in such capacity, the
                  "Collateral Agent") for the Lenders, and DEUTSCHE BANK AG, New
                  York Branch, as documentation agent (in such capacity, the
                  "Documentation Agent").

      A. Pursuant to the Credit Agreement, the Lenders and the Issuing Bank have
extended, and have agreed to extend, credit to the Borrower.

      B. The Borrower has requested that the Required Lenders agree to amend the
Credit Agreement as provided herein.

      C. The Required Lenders are willing so to amend the Credit Agreement
pursuant to the terms and subject to the conditions set forth herein.

      D. Capitalized terms used but not defined herein shall have the meanings
assigned to them in the Credit Agreement.

      Accordingly, In consideration of the mutual agreements herein contained
and other good and valuable consideration, the sufficiency and receipt of which
are hereby acknowledged, the parties hereto agree as follows:

      SECTION 1. Amendments to Section 1.01. (a) The definition of "EBITDA" in
Section 1.01 of the Credit Agreement is hereby amended by deleting the phrase
"the Leverage Ratio and the Senior Leverage Ratio" in the last sentence thereof
and substituting therefor the phrase "all financial covenants".

      (b) The definition of "Interest Expense" in Section 1.01 of the Credit
Agreement is hereby amended by adding the following sentence at the end thereof:
"For purposes of determining Interest Expense for the quarters ended September
30, 1999, December 31, 1999, and March 31, 2000, Interest Expense shall be
calculated on a pro forma basis."

      SECTION 2. Representations and Warranties. To induce the other parties
hereto to enter into this Amendment, the Borrower represents and warrants to
each of the Lenders, the Administrative Agent, the Issuing Banks, the Collateral
Agent and the Documentation Agents that, after giving effect to this Amendment,
(a) the representations and warranties set forth in Article III of the Credit
Agreement are true and correct in all material respects on and as of the date
hereof, except to the extent such


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representations and warranties expressly relate to an earlier date, and (b) no
Default or Event of Default has occurred and is continuing.

      SECTION 3. Effectiveness. This Amendment shall become effective as of the
date first written above on the date on which the Administrative Agent shall
have received counterparts of this Amendment that, when taken together, bear the
signatures of the Borrower, the Guarantors and the Required Lenders.

      SECTION 4. Effect of Amendment. Except as expressly set forth herein, this
Amendment shall not by implication or otherwise limit, impair, constitute a
waiver of, or otherwise affect the rights and remedies of the Lenders, the
Issuing Banks, the Collateral Agent, the Administrative Agent or the
Documentation Agents under the Credit Agreement or any other Loan Document, and
shall not alter, modify, amend or in any way affect any of the terms,
conditions, obligations, covenants or agreements contained in the Credit
Agreement or any other Loan Document, all of which are ratified and affirmed in
all respects and shall continue in full force and effect. Nothing herein shall
be deemed to entitle any Loan Party to a consent to, or a waiver, amendment,
modification or other change of, any of the terms, conditions, obligations,
covenants or agreements contained in the Credit Agreement or any other Loan
Document in similar or different circumstances. This Amendment shall apply and
be effective only with respect to the provisions of the Credit Agreement
specifically referred to herein. After the date hereof, any reference to the
Credit Agreement shall mean the Credit Agreement, as modified hereby. This
Amendment shall constitute a "Loan Document" for all purposes of the Credit
Agreement and the other Loan Documents.

      SECTION 5. Counterparts. This Amendment may be executed in any number of
counterparts and by different parties hereto in separate counterparts, each of
which when so executed and delivered shall be deemed an original, but all such
counterparts together shall constitute but one and the same contract. Delivery
of an executed counterpart of a signature page of this Amendment by facsimile
transmission shall be as effective as delivery of a manually executed
counterpart hereof.

      SECTION 6. Applicable Law. THIS AMENDMENT SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

      SECTION 7. Headings. The headings of this Amendment are for purposes of
reference only and shall not limit or otherwise affect the meaning hereof.

      SECTION 8. Expenses. The Borrower agrees to reimburse the Administrative
Agent for all out-of-pocket expenses in connection with this Amendment,
including the reasonable fees, charges and disbursements of Cravath, Swaine &
Moore, counsel for the Administrative Agent.

      SECTION 9. Acknowledgment of Guarantors. Each of the Guarantors hereto
hereby acknowledges receipt and notice of, and consents to the terms of, this
Amendment.


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      IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly created by their duly authorized officers, all as of the date and year
first above written.

                                ANTEON CORPORATION,

                                     by: /s/ Carlton B. Crenshaw
                                        ---------------------------------------
                                        Name: Carlton B. Crenshaw
                                        Title: Sr. V.P. Finance and Admin.


                                ANALYSIS & TECHNOLOGY, INC.,

                                     by: /s/ Carlton B. Crenshaw
                                        ---------------------------------------
                                        Name: Carlton B. Crenshaw
                                        Title: Vice President


                                INTERACTIVE MEDIA CORP.

                                     by: /s/ David M. Nolf
                                        ---------------------------------------
                                        Name: David M. Nolf
                                        Title: Secretary


                                TECHMATICS, INC.

                                     by: /s/ Carlton B. Crenshaw
                                        ---------------------------------------
                                        Name: Carlton B. Crenshaw
                                        Title: V.P. and Treasurer


                                VECTOR DATA SYSTEMS, INC.,

                                     by: /s/ Carlton B. Crenshaw
                                        ---------------------------------------
                                        Name: Carlton B. Crenshaw
                                        Title: Treasurer


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                                CREDIT SUISSE FIRST BOSTON, individually
                                and as Administrative Agent and Issuing Bank

                                     by: /s/ Joel Glodowski
                                        ---------------------------------------
                                        Name: Joel Glodowski
                                        Title: Managing Director

                                     by: /s/ Robert Hetu
                                        ---------------------------------------
                                        Name: ROBERT Hetu
                                        Title: Vice President


                                MELLON BANK, N.A., individually and as
                                Collateral Agent, Swingline Lender and
                                Syndication Agent,

                                     by:
                                        ---------------------------------------
                                        Name:
                                        Title:


                                DEUTSCHE BANK AG, New York Branch, as
                                Documentation Agent,

                                     by:
                                        ---------------------------------------
                                        Name:
                                        Title:

                                     by:
                                        ---------------------------------------
                                        Name:
                                        Title:


                                DEUTSCHE BANK AG, New York and/or
                                Cayman Islands Branches, as Lender

                                     by:
                                        ---------------------------------------
                                        Name:
                                        Title:

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                                CREDIT SUISSE FIRST BOSTON, individually
                                and as Administrative Agent and Issuing Bank,

                                     by:
                                        ---------------------------------------
                                        Name:
                                        Title:

                                     by:
                                        ---------------------------------------
                                        Name:
                                        Title:


                                MELLON BANK, N.A., individually and as
                                Collateral Agent, Swingline Lender and
                                Syndication Agent,

                                     by: /s/ David H. Reed
                                        ---------------------------------------
                                        Name: David H. Reed
                                        Title: First Vice President


                                DEUTSCHE BANK AG, New York Branch, as
                                Documentation Agent,

                                     by:
                                        ---------------------------------------
                                        Name:
                                        Title:

                                     by:
                                        ---------------------------------------
                                        Name:
                                        Title:


                                DEUTSCHE BANK AG, New York and/or
                                Cayman Islands Branches, as Lender,

                                     by:
                                        ---------------------------------------
                                        Name:
                                        Title:

<PAGE>

                                CREDIT SUISSE FIRST BOSTON, individually
                                and as Administrative Agent and Issuing Bank,

                                     by:
                                        ---------------------------------------
                                        Name:
                                        Title:

                                     by:
                                        ---------------------------------------
                                        Name:
                                        Title:


                                MELLON BANK, N.A., individually and as
                                Collateral Agent, Swingline Lender and
                                Syndication Agent,

                                     by:
                                        ---------------------------------------
                                        Name:
                                        Title:


                                DEUTSCHE BANK AG, New York Branch, as
                                Documentation Agent,

                                     by: /s/ Paul Hatfield
                                        ---------------------------------------
                                        Name: Paul Hatfield
                                        Title: Vice President

                                     by: /s/ Robert Wood
                                        ---------------------------------------
                                        Name: Robert Wood
                                        Title: Director


                                DEUTSCHE BANK AG, New York and/or
                                Cayman Islands Branches, as Lender,

                                     by: /s/ Paul Hatfield
                                        ---------------------------------------
                                        Name: Paul Hatfield
                                        Title: Vice President

                                     by: /s/ Robert Wood
                                        ---------------------------------------
                                        Name: Robert Wood
                                        Title: Director

<PAGE>

                                                      SIGNATURE PAGE TO
                                                      AMENDMENT NO 2.
                                                      DATED AS OF
                                                      MARCH 29, 2000
                                                      TO ANTEON
                                                      CORPORATION CREDIT
                                                      AGREEMENT

NAME OF INSTITUTION: Bank Polska Kasa Opieki S.A., New York Branch
                    ----------------------------------------------


                    by /s/ Hussein B. El Tawil
                      --------------------------------------------
                       Name: Hussein B. El Tawil
                       Title: Vice President


<PAGE>

                                                      SIGNATURE PAGE TO
                                                      AMENDMENT NO 2.
                                                      DATED AS OF
                                                      MARCH 29, 2000
                                                      TO ANTEON
                                                      CORPORATION CREDIT
                                                      AGREEMENT

NAME OF INSTITUTION: FLEET NATIONAL BANK, BOSTON, MASSACHUSETTS
                    ----------------------------------------------


                    by /s/ Roger C. Boucher
                      --------------------------------------------
                       Name: Roger C. Boucher
                       Title: Senior Vice President

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                                                      SIGNATURE PAGE TO
                                                      AMENDMENT NO 2.
                                                      DATED AS OF
                                                      MARCH 29, 2000
                                                      TO ANTEON
                                                      CORPORATION CREDIT
                                                      AGREEMENT

NAME OF INSTITUTION: PNC BANK
                    ----------------------------------------------


                    by /s/ Daniel J. Paull
                      --------------------------------------------
                       Name: Daniel J. Paull
                       Title: Vice President

<PAGE>

                                                      SIGNATURE PAGE TO
                                                      AMENDMENT NO 2.
                                                      DATED AS OF
                                                      MARCH 29, 2000
                                                      TO ANTEON
                                                      CORPORATION CREDIT
                                                      AGREEMENT

NAME OF INSTITUTION: TRANSAMERICA BUSINESS CREDIT CORPORATION
                    ----------------------------------------------


                    by /s/ Perry Vavoules
                      --------------------------------------------
                       Name: Perry Vavoules
                       Title: Senior Vice President