UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, DC 20549 SCHEDULE 13G UNDER THE SECURITIES EXCHANGE ACT OF 1934 (AMENDMENT NO. )* MERCURY COMPUTER SYSTEMS INC ________________________________________________________________________ (Name of Issuer) Common ________________________________________________________________________ (Title of Class of Securities) 589378108 _______________________________ (CUSIP Number) Check the following box if a fee is being paid with this statement [ ]. (A fee is not required only if the filing person: (1) has a previous statement on file reporting beneficial ownership of more than five percent of the class of securities described in Item 1; and (2) has filed no amendment subsequent thereto reporting beneficial ownership of five percent or less of such class.) (See Rule 13d-7.) *The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page. The information required in the remainder of this cover page shall not be deemed to be filed for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes). Page 1 of 2 pages CUSIP No. 589378108 13G ________________________________________________________________________ 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Massachusetts Mutual Life Insurance Company 04-1590850 ________________________________________________________________________ 2 CHECK THE APPROPRIATE BOX IF MEMBER OF A GROUP (A) _______ (B) __x____ ________________________________________________________________________ 3 SEC USE ONLY ________________________________________________________________________ 4 CITIZENSHIP OF PLACE OF ORGANIZATION Commonwealth of Massachusetts ________________________________________________________________________ 5 SOLE VOTING POWER NUMBER OF SHARES 500,000 ____________________________________________________ BENEFICIALLY 6 SHARED VOTING POWER OWNED BY EACH not applicable ____________________________________________________ REPORTING 7 SOLE DISPOSITIVE POWER PERSON WITH 500,000 ____________________________________________________ 8 SHARED DISPOSITIVE POWER not applicable ________________________________________________________________________ 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 500,000 ________________________________________________________________________ 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES * not applicable ________________________________________________________________________ 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 5.05% ________________________________________________________________________ 12 TYPE OF REPORTING PERSON * IC (insurance company) ________________________________________________________________________ * SEE INSTRUCTION BEFORE FILLING OUT! Page 2 of 2 pages CUSIP No. 589378108 13G ________________________________________________________________________ 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON MassMutual Corporate Investors 04-2483041 ________________________________________________________________________ 2 CHECK THE APPROPRIATE BOX IF MEMBER OF A GROUP (A) _______ (B) __x____ ________________________________________________________________________ 3 SEC USE ONLY ________________________________________________________________________ 4 CITIZENSHIP OF PLACE OF ORGANIZATION Commonwealth of Massachusetts ________________________________________________________________________ 5 SOLE VOTING POWER NUMBER OF SHARES 500,000 ____________________________________________________ BENEFICIALLY 6 SHARED VOTING POWER OWNED BY EACH not applicable ____________________________________________________ REPORTING 7 SOLE DISPOSITIVE POWER PERSON WITH 500,000 ____________________________________________________ 8 SHARED DISPOSITIVE POWER not applicable ________________________________________________________________________ 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 500,000 ________________________________________________________________________ 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES * not applicable ________________________________________________________________________ 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 5.05% ________________________________________________________________________ 12 TYPE OF REPORTING PERSON * IV (investment company) ________________________________________________________________________ * SEE INSTRUCTION BEFORE FILLING OUT! ITEM 1(a). Name of Issuer: Mercury Computer Systems, Inc. ITEM 1(b). Address of Issuer's Principal Executive Offices: 199 Riverneck Road Chelmsford, MA 01824 ITEM 2(a). Name of Person Filing: This statement is filed on behalf of Massachusetts Mutual Life Insurance Company and MassMutual Corporate Investors, which together may be regarded as a group for the purpose of this statement. This statement is signed on behalf of both the aforementioned parties, and therefore it does not include a separate agreement providing for a joint filing. ITEM 2(b). Address of Principal Business Office: MASSACHUSETTS MUTUAL LIFE INSURANCE COMPANY 1295 State Street Springfield, Massachusetts 01111 MASSMUTUAL CORPORATE INVESTORS 1295 State Street Springfield, Massachusetts 01111 ITEM 2(c). Citizenship MASSACHUSETTS MUTUAL LIFE INSURANCE COMPANY is organized under the laws of the Commonwealth of Massachusett MASSMUTUAL CORPORATE INVESTORS is organized under the laws of the Commonwealth of Massachusett ITEM 2(d). Title of Class of Securities: Common Stock ITEM 2(e). CUSIP NUMBER: 589378108 ITEM 3. This statement is filed pursuant to Rule 13d-1(b) by Massachusetts Mutual Life Insurance Company, an insurance company as defined in Section 3(a)(19), and MassMutual Corporate Investors, an investment company registered under Section 8 of the Investment Company Act of 1940, which together may be regarded as a group pursuant to Rule 13d-1(b) (ii) (H). ITEM 4. Ownership: This statement if filed to report information as of January 29, 1998. (a) Amount Beneficially Owned: Massachusetts Mutual Life Insurance Company, and MassMutual Corporate Investors each own 500,000 shares of common stock. Total shares of common stock owned directly and indirectly: 1,000,000. The filing of this statement shall not be construed as an admission that Massachusetts Mutual Life Insurance Company and MassMutual Corporate Investors, Investors, are for the purposes of sections 13(d) and 13(g) of the Securities Exchange Act of 1934, the beneficial owners of any common stock of the issuer. (b) Percent of Class: Percentage of ownership is calculated as follows: 1,000,000 (shs held) / 9,868,223 (shares outstanding) = 10.1% (c) Powers: Massachusetts Mutual Life Insurance Company and MassMutual Corporate Investors, each have sole power to vote or dispose of 500,000 shares of common stock. ITEM 5. Ownership of Five Percent or Less of a Class: Not Applicable ITEM 6. Ownership of More Than Five Percent on Behalf of Another Person: Not applicable ITEM 7. Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company: Note applicable ITEM 8. Identification and Classification of Members of the Group: not applicable ITEM 9. Notice of Dissolution of the Group: Not applicable ITEM 10. Certification: By signing below, MASSACHUSETTS MUTUAL LIFE INSURANCE COMPANY and MASSMUTUAL CORPORATE INVESTORS certify to the best of their knowledge and belief, the securities referred to above were acquired in the ordinary course of business and were not acquired for the purpose of and do not have the effect of changing or influencing the control of the issuer of such securities and were not acquired in connection with or as a participant in any transaction having such purpose or effect. Signature --------- After reasonable inquiry and to the best of knowledge and belief, MASSACHUSETTS MUTUTAL LIFE INSURANCE COMPANY and MASSMUTUAL CORPORATE INVESTORS, INVESTORS, certify that the information set forth in this statement is true, complete and correct. February 9, 1998 February 9, 1998 _____________________ _____________________ Date Date MASSACHUSETTS MUTUAL MASSMUTUAL CORPORATE LIFE INSURANCE COMPANY INVESTORS By: signature By: signature Richard C. Morrison Richard C. Morrison Managing Director Vice President _________________________ _________________________ (Print Name and Title (Print Name and Title of Person Signing) of Person Signing)