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                                                                   EXHIBIT 10.18

                            SECURED PROMISSORY NOTE


                                                                January 20, 2000
$231,023.90                                                     Washington, D.C.

     FOR VALUE RECEIVED, George M. Cathey (the "Maker") promises to pay to MIL
3, Incorporated, a Delaware corporation (the "Company"), or order, at the
offices of the Company or at such other place as the holder of this Note may
designate, the principal sum of $231,023.90, together with interest on the
unpaid principal balance of this Note from time to time outstanding equal to
6.0% per year until paid in full.  Principal and accrued interest shall be due
and payable in full on the earlier of (i) the second anniversary of the date of
this Note or (ii) the first anniversary of the closing of an initial public
offering of equity securities of the Company pursuant to a registration
statement filed with the Securities and Exchange Commission.

     Interest on this Note shall be computed on the basis of a year of 365 days
for the actual number of days elapsed.  All payments by the Maker under this
Note shall be in immediately available funds.

     Payment of this Note is secured by a security interest in certain property
of the Maker pursuant to a pledge agreement of even date herewith between the
Maker and the Company (the "Pledge Agreement").

     The Maker's obligations under this Note are also fully recoverable from the
Maker's personal assets.

     This Note shall become immediately due and payable without notice or demand
upon the occurrence at any time of any of the following events of default
(individually, "an Event of Default" and collectively, "Events of Default"):

     (1)  the effective date of termination of the Maker's employment with the
          Company, if the Maker's employment with the Company shall be
          terminated by the Company for "good cause" as set forth in Section 2.1
          of the Employment Agreement, dated December 4, 1995, between the Maker
          and the Company (the "Employment Agreement");

     (2)  the date of the final determination of any breach by the Maker of (i)
          the covenant not to compete set forth in Section 1.6 of the Employment
          Agreement or (ii) any of the terms of the Agreement Regarding Creative
          Works, Inventions and Confidentiality, dated as of April 8, 1991,
          between the Maker and the Company;

     (3)  the institution against the Maker or any endorser or guarantor of this
          Note of any proceedings under the United States Bankruptcy Code or any
          other federal or state bankruptcy, reorganization, receivership,
          insolvency or other similar law affecting the rights of creditors
          generally, which proceeding is not dismissed within thirty (30) days
          of filing;
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     (4)  the institution by the Maker or any endorser or guarantor of this Note
          of any proceedings under the United States Bankruptcy Code or any
          other federal or state bankruptcy, reorganization, receivership,
          insolvency or other similar law affecting the rights of creditors
          generally or the making by the Maker or any endorser or guarantor of
          this Note of a composition or an assignment or trust mortgage for the
          benefit of creditors;

     (5)  the occurrence of any event of default under the Pledge Agreement; or

     (6)  if the Maker dies or becomes incapacitated, or if a conservator or
          guardian of the Maker is appointed, or if the Maker suffers any other
          legal disability.

     Upon the occurrence of an Event of Default, the holder shall have then, or
at any time thereafter, all of the rights and remedies afforded by the Uniform
Commercial Code as from time to time in effect in the District of Columbia or
afforded by other applicable law.

     Every amount overdue under this Note shall bear interest from and after the
date on which such amount first became overdue at an annual rate which is two
(2) percentage points above the rate per year specified in the first paragraph
of this Note.  Such interest on overdue amounts under this Note shall be payable
on demand and shall accrue and be compounded monthly until the obligation of the
Maker with respect to the payment of such interest has been discharged (whether
before or after judgment).

     In no event shall any interest charged, collected or reserved under this
Note exceed the maximum rate then permitted by applicable law and if any such
payment is paid by the Maker, then such excess sum shall be credited by the
holder as a payment of principal.

     All payments by the Maker under this Note shall be made without set-off or
counterclaim and be free and clear and without any deduction or withholding for
any taxes or fees of any nature whatever, unless the obligation to make such
deduction or withholding is imposed by law.  The Maker shall pay and save the
holder harmless from all liabilities with respect to or resulting from any delay
or omission to make any such deduction or withholding required by law.

     Whenever any amount is paid under this Note, all or part of the amount paid
may be applied to principal or interest in such order and manner as shall be
determined by the holder in its discretion.

     No reference in this Note to the Pledge Agreement or any guaranty or other
document shall impair the obligation of the Maker to pay all amounts under this
Note strictly in accordance with the terms of this Note.

     The Maker agrees to pay on demand all costs of collection, including
reasonable attorneys' fees, incurred by the holder in enforcing the obligations
of the Maker under this Note.

     No delay or omission on the part of the holder in exercising any right
under this Note or the Pledge Agreement shall operate as a waiver of such right
or of any other right of such holder, nor shall any delay, omission or waiver on
any one occasion be deemed a bar to or waiver of the same or any other right on
any future occasion.  The Maker and every endorser or guarantor of

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this Note regardless of the time, order or place of signing waives presentment,
demand, protest and notices of every kind and assents to any extension or
postponement of the time of payment or any other indulgence, to any
substitution, exchange or release of collateral, and to the addition or release
of any other party or person primarily or secondarily liable.

     This Note may be prepaid in whole or in part at any time or from time to
time by the Maker.  Any such prepayment shall be without premium or penalty.

     None of the terms or provisions of this Note may be excluded, modified or
amended except by a written instrument duly executed on behalf of the holder
expressly referring to this Note and setting forth the provision so excluded,
modified or amended.

     All rights and obligations hereunder shall be governed by the laws of the
District of Columbia and this Note is executed as an instrument under seal.

     IN WITNESS WHEREOF, this Note has been executed by an authorized
representative of the undersigned as of the date first written above.


                                             /s/ George M. Cathey
                                             -----------------------
                                             George M. Cathey


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