UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K/A

(Amendment No. 1)

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

December 30, 2011

Date of Report (Date of earliest event reported)

MERCURY COMPUTER SYSTEMS, INC.

(Exact Name of Registrant as Specified in its Charter)

(978) 256-1300

(Registrant’s telephone number, including area code)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

EXPLANATORY NOTE

On December 30, 2011, Mercury Computer Systems, Inc. (the “Company”) filed a Form 8-K (the “Original 8-K”) to report on that date, that its wholly-owned subsidiary, King Merger Inc. ( the “Merger Sub”), completed the acquisition of KOR Electronics (“KOR”) with the Merger Sub being merged with and into KOR and with KOR continuing as the surviving company and a wholly-owned subsidiary of the Company (the “Merger”). By operation of the Merger, the Company acquired both KOR and its wholly-owned subsidiary, Paragon Dynamics, Inc. (“PDI”).

The purpose of this amendment to the Original 8-K is to provide the historical financial statements of KOR required by Item 9.01(a) of Form 8-K and the pro forma financial information required by Item 9.01(b) of Form 8-K, which information was excluded from the Original 8-K, in reliance upon Item 9.01(a)(4) and Item 9.01(b)(2) of Form 8-K.

The audited consolidated financial statements of KOR Electronics and Subsidiary as of December 31, 2010 and for the year ended December 31, 2010 and accompanying notes are included as Exhibit 99.1 hereto and are incorporated herein by reference.

The unaudited condensed consolidated financial statements of KOR Electronics and Subsidiary as of September 30, 2011 and December 31, 2010 and for the three and nine months ended September 30, 2011 and 2010 and accompanying notes are included as Exhibit 99.2 hereto and are incorporated herein by reference.

The following Unaudited Pro Forma Condensed Combined Financial Statements required pursuant to Item 9.01(b) of Form 8-K are included as Exhibit 99.3 hereto and are incorporated herein by reference:

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.