SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person* OBRIEN WILLIAM K (Last) (First) (Middle) 199 RIVERNECK ROAD (Street) CHELMSFORD MA 01844 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 11/17/2008	3. Issuer Name and Ticker or Trading Symbol MERCURY COMPUTER SYSTEMS INC [ MRCY ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) X Director 10% Owner Officer (give title below) Other (specify below)	5. If Amendment, Date of Original Filed (Month/Day/Year)
			6. Individual or Joint/Group Filing (Check Applicable Line) X Form filed by One Reporting Person Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
No Shares Beneficially Owned	0	D

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

	Karl D. Noone, Attorney-in-fact	11/18/2008
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (b)(v).
** 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 is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

LIMITED POWER OF ATTORNEYLIMITED POWER OF ATTORNEY
FOR
MERCURY COMPUTER SYSTEMS, INC.
SECTION 16(a) FILINGS

Know all by these presents, that the undersigned hereby constitutes and appoints
each of Robert E. Hult, Senior Vice-President, Chief Financial Officer and
Treasurer, Karl D. Noone, Vice-President and Corporate Controller and Alex A.
Van Adzin, Vice-President , General Counsel and Corporation Secretary, acting
singly, the undersigned's true and lawful attorney-in-fact to:
(1) prepare, execute in the undersigned's name and on the undersigned's behalf,
and submit to the U.S. Securities and Exchange Commission (the "SEC") a Form ID,
including amendments thereto, and any other documents necessary or appropriate
to obtain codes and passwords enabling the undersigned to make electronic
filings with the SEC of reports required by Section 16(a) of the Securities
Exchange Act of 1934 or any rule or regulation of the SEC;
(2) execute for and on behalf of the undersigned, in the undersigned's capacity
as an officer, director and/or shareholder of Mercury Computer Systems, Inc.
(the "Company"), Forms 3, 4 and 5, and amendments thereto, in accordance with
Section 16(a) of the Securities Exchange Act of 1934, as amended (the "Exchange
Act") and the rules thereunder;
(3) do and perform any and all acts for and on behalf of the undersigned which
may be necessary or desirable to complete and execute any such Form 3, 4 or 5,
or amendments thereto, and timely file such form with the United States
Securities and Exchange Commission (the "SEC") and any stock exchange or similar
authority; and
(4) take any other action of any type whatsoever which, in the opinion of such
attorney-in-fact, may be necessary or desirable in connection with the foregoing
authority, it being understood that the documents executed by each such
attorney-in-fact on behalf of the undersigned pursuant to this Limited Power of
Attorney shall be in such form and shall contain such terms and conditions as
such attorney-in-fact may approve, provided, however, that the undersigned does
not grant to each such power-of-attorney the right to engage in any transactions
involving the securities of the Company on behalf of the undersigned, including
without limitation, the right to purchase or sell any securities of the Company.
The undersigned hereby grants to each such attorney-in-fact full power and
authority to do and perform any and every act and thing whatsoever requisite,
necessary, or proper to be done in the exercise of any of the rights and powers
herein granted, as fully to all intents and purposes as the undersigned might or
could do if personally present, with full power of substitution or revocation,
hereby ratifying and confirming all that each such attorney-in-fact, or each
such attorney-in-fact's substitute or substitutes (any such substitute also
being referred to herein as an "attorney-in-fact"), shall lawfully do or cause
to be done by virtue of this Limited Power of Attorney and the rights and powers
herein granted. The undersigned acknowledges that each attorney-in-fact, in
serving in such capacity at the request of the undersigned or such
attorney-in-fact, is not assuming, nor is the Company assuming, any of the
undersigned's responsibilities to comply with Section 16 of the Exchange Act.

The undersigned agrees that each such attorney-in-fact shall not be liable for
any error of judgment or for any act done or omitted to be done or for any
mistake of fact or law except for each such attorney-in-fact's own bad faith,
and the undersigned agrees to indemnify and to hold each such attorney-in-fact
harmless against any loss, claim, damage, liability or cost incurred on each
such attorney-in-fact's part arising out of or in connection with acts
undertaken or omitted to be taken as an attorney-in-fact hereunder.
This Limited Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file Forms 3, 4, and 5 with respect to the
undersigned's holdings of
and transactions in securities of the Company, unless earlier revoked by the
undersigned in a signed writing delivered to the foregoing attorneys-in-fact.
This Limited Power of Attorney may be filed with the SEC as a confirming
statement of the authority granted herein.
IN WITNESS WHEREOF, the undersigned has caused this Limited Power of Attorney to
be executed as of this 15 day of November, 2008.

/s/ William K. O'Brien