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                                                                   Exhibit 10.15

                       SUPPLEMENT NO 1 dated as of October 14, 1999, to the
                  Security Agreement dated as of June 23, 1999, among ANTEON
                  CORPORATION, a Virginia corporation (the "BORROWER"), each
                  subsidiary of the Borrower listed on Schedule I thereto
                  (each such subsidiary individually a "SUBSIDIARY GUARANTOR"
                  and collectively, the "SUBSIDIARY GUARANTORS"; the
                  Subsidiary Guarantors and the Borrower are referred to
                  collectively herein as the "GRANTORS") and MELLON BANK,
                  N.A., a national banking association ("MELLON"), as
                  collateral agent (in such capacity, the "COLLATERAL AGENT")
                  for the Secured Parties (as defined herein).

     A. Reference is made to (a) the Credit Agreement dated as of June 23,
1999 (as amended, supplemented or otherwise modified from time to time, the
"CREDIT AGREEMENT"), among the Borrower, the lenders from time to time party
thereto (the "LENDERS"), Credit Suisse First Boston, a bank organized under
the laws of Switzerland, acting through its New York branch ("CSFB"), as
administrative agent for the Lenders (in such capacity, the "ADMINISTRATIVE
AGENT") and as issuing bank, Mellon, as Collateral Agent, syndication agent
and swingline lender, and Deutsche Bank AG, New York Branch, as documentation
agent, and (b) the Subsidiary Guarantee Agreement dated as of June 23, 1999
(as amended, supplemented or otherwise modified from time to time, the
"GUARANTEE AGREEMENT"), among the Subsidiary Guarantors and the Collateral
Agent.

     B. Capitalized terms used herein and not otherwise defined herein shall
have the meanings assigned to such terms in the Security Agreement or the
Credit Agreement, as applicable.

     C. The Grantors have entered into the Security Agreement in order to
induce the Lenders to make Loans and the Issuing Bank to issue Letters of
Credit. Section 7.15 of Security Agreement provides that additional
Subsidiaries of the Borrower may become Grantors under the Security Agreement
by execution and delivery of an instrument in the form of this Supplement.
The undersigned Subsidiary (the "NEW GRANTOR") is executing this Supplement
in accordance with the requirements of the Credit Agreement to become a
Grantor under the Security Agreement in order to induce the Lenders to make
additional Loans and the Issuing Bank to issue additional Letters of Credit
and as consideration for Loans previously made and Letters of Credit
previously issued.

     Accordingly, the Collateral Agent and the New Grantor agree as follows:


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     SECTION 1. In accordance with Section 7.15 of the Security Agreement,
the New Grantor by its signature below becomes a Grantor under the Security
Agreement with the same force and effect as if originally named therein as a
Grantor and the New Grantor hereby (a) agrees to all the terms and provisions
of the Security Agreement applicable to it as a Grantor thereunder and (b)
represents and warrants that the representations and warranties made by it as
a Grantor thereunder are true and correct on and as of the date hereof. In
furtherance of the foregoing, the New Grantor, as security for the payment
and performance in full of the Obligations (as defined in the Security
Agreement), does hereby create and grant to the Collateral Agent, its
successors and assigns, for the benefit of the Secured Parties, their
successors and assigns, a security interest in and lien on all of the New
Grantor's right, title and interest in and to the Collateral (as defined in
the Security Agreement) of the New Grantor. Each reference to a "Grantor" in
the Security Agreement shall be deemed to include the New Grantor. The
Security Agreement is hereby incorporated herein by reference.

     SECTION 2. The New Grantor represents and warrants to the Collateral
Agent and the other Secured Parties that this Supplement has been duly
authorized, executed and delivered by it and constitutes its legal, valid
and binding obligation, enforceable against it in accordance with its terms.

     SECTION 3. This Supplement may be executed in counterparts (and by
different parties hereto on different counterparts), each of which shall
constitute an original, but all of which when taken together shall constitute
a single contract. This Supplement shall become effective when the Collateral
Agent shall have received counterparts of this Supplement that, when taken
together, bear the signatures of the New Grantor and the Collateral Agent.
Delivery of an executed signature page to this Supplement by facsimile
transmission shall be as effective as delivery of a manually signed
counterpart of this Supplement.

     SECTION 4. The New Grantor hereby represents and warrants that (a) set
forth on Schedule I attached hereto is a true and correct schedule of the
location of any and all Collateral of the New Grantor and (b) set forth
under its signature hereto, is the true and correct location of the chief
executive office of the New Grantor.

     SECTION 5. Except as expressly supplemented hereby, the Security
Agreement shall remain in full force and effect.

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

     SECTION 7. In case any one or more of the provisions contained in this
Supplement should be held invalid, illegal or unenforceable in any respect,
the validity, legality and enforceability of the remaining provisions
contained herein


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and in the Security Agreement shall not in any way be affected or impaired
thereby (it being understood that the invalidity of a particular provision in
a particular jurisdiction shall not in and of itself affect the validity of
such provision in any other jurisdiction). The parties hereto shall endeavor
in good-faith negotiations to replace the invalid, illegal or unenforceable
provisions with valid provisions the economic effect of which comes as close
as possible to that of the invalid, illegal or unenforceable provisions.

     SECTION 8. All communications and notices hereunder shall be in writing
and given as provided in Section 7.01 of the Security Agreement. All
communications and notices hereunder to the New Grantor shall be given to it
at the address set forth under its signature below.

     SECTION 9. The New Grantor agrees to reimburse the Collateral Agent for
its reasonable out-of-pocket expenses in connection with this Supplement,
including the reasonable fees, other charges and disbursements of counsel for
the Collateral Agent.

     IN WITNESS WHEREOF, the New Grantor and the Collateral Agent have duly
executed this Supplement to the Security Agreement as of the day and year
first above written.

                                       ANTEON-CITI, LLC,

                                       by: /s/ Carlton B. Crenshaw
                                          -----------------------------------
                                          Name: Carlton B. Crenshaw
                                          Title: Vice President
                                          Address: 3211 Jermantown Rd.
                                                   Fairfax, VA 22030

                                       MELLON BANK N.A., as Collateral Agent,

                                       by: /s/ Leslie A. Grizzard
                                          -----------------------------------
                                          Name: Leslie A. Grizzard
                                          Title: Vice President

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                                                                   SCHEDULE I
                                                   to Supplement No. 1 to the
                                                           Security Agreement

                           LOCATION OF COLLATERAL

<TABLE>
<CAPTION>

Description                                  Location
-----------                                  --------
<S>                                          <C>
Office Furniture, Computer                   Old Corner Store
Equipment                                    U. S. Route 2
                                             Jefferson, NH 03583

Office Furniture, Computer                   11120 Wurzbach Rd.
Equipment                                    Suite 304
                                             San Antonio, TX 78230

Software Source Code                         Anteon Corporation
                                             2770 East Gunter Park Dr.
                                             Montgomery, AL 36109

</TABLE>