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                     U.S. SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                     FORM 3

            INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

    Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934,
       Section 17(a) of the Public Utility Holding Company Act of 1935 or
               Section 30(f) of the Investment Company Act of 1940


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1. Name and Address of Reporting Person

     Johnsen            Russell                    K.
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   (Last)               (First)                 (Middle)

     26 Great Pond Drive
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                                    (Street)
     Boxford               MA                   01921

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   (City)               (State)                 (Zip)


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2. Date of Event Requiring Statement (Month/Day/Year)

     1/15/2001

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3. IRS or Social Security Number of Reporting Person (Voluntary)


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4. Issuer Name and Ticker or Trading Symbol

     Mercury Computer Systems, Inc.   MRCY
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5 Relationship of Reporting Person to Issuer
   (Check all applicable)

   [ X ]   Director                             [   ]   10% Owner
   [   ]   Officer (give title below)           [   ]   Other (specify below)



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6. If Amendment, Date of Original (Month/Year)


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             Table I -- Non-Derivative Securities Beneficially Owned
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3. Ownership Form: 2. Amount of Securities Direct (D) or 1. Title of Security Beneficially Owned Indirect (I) 4. Nature of Indirect Beneficial Ownership (Instr. 4) (Instr. 4) (Instr. 5) (Instr.5) - ------------------------------------------------------------------------------------------------------------------------------------ None None - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ ====================================================================================================================================
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. (Print or Type Responses) FORM 3 (continued) Table II -- Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities) ================================================================================
5. Owner- 3. Title and Amount of Securities ship Underlying Derivative Security Form of 2. Date Exercisable (Instr. 4) Derivative and Expiration Date --------------------------------- 4. Conver- Security: (Month/Day/Year) Amount sion or Direct 7. Nature of ---------------------- or Exercise (D) or Indirect Date Expira- Number Price of Indirect Beneficial 1. Title of Security Exer- tion of Derivative (I) Ownership (Instr. 4) cisable Date Title Shares Security (Instr.5) (Instr. 5) - ------------------------------------------------------------------------------------------------------------------------------------ None - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ ==================================================================================================================================== Explanation of Responses:
/s/ Russell K. Johnsen March 30, 2001 - --------------------------------------------- ----------------------- **Signature of Reporting Person Date ** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a). Note: File three copies of this Form, one of which must be manually signed. If space provided is insufficient. See Instruction 6 for procedure.