UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14D-9/A

(Amendment No. 4)

SOLICITATION/RECOMMENDATION STATEMENT
UNDER SECTION 14(d)(4) OF THE SECURITIES EXCHANGE ACT OF 1934

Global Defense Technology & Systems, Inc.

(Name of Subject Company)

Global Defense Technology & Systems, Inc.

(Name of Person(s) Filing Statement)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

37950B107
(CUSIP Number of Class of Securities)

John Hillen

President and Chief Executive Officer

Global Defense Technology & Systems, Inc.

1501 Farm Credit Drive, Suite 2300, McLean, VA 22102-5011

703-738-2840

 (Name, Address, and Telephone Number of Person Authorized
to Receive Notices and Communications on Behalf of the Person(s) Filing Statement)

With Copies to:

o            Check the box if the filing relates solely to preliminary communications made before the commencement of a tender offer.

This Amendment No. 4 amends and supplements the Solicitation/Recommendation Statement on Schedule 14D-9 initially filed with the Securities and Exchange Commission (the “Commission”) by Global Defense Technology & Systems, Inc. (the “Company”) on March 7, 2011, as amended by Amendment No. 1 filed with the Commission by the Company on March 16, 2011, Amendment No. 2 filed with the Commission by the Company on March 17, 2011 and Amendment No. 3 filed with the Commission on March 22, 2011 (such Schedule 14D-9, as so amended, the “Schedule 14D-9”). The Schedule 14D-9 relates to the tender offer by Sentinel Acquisition Corporation, a Delaware corporation and direct, wholly owned subsidiary of Sentinel Acquisition Holdings Inc., a Delaware corporation, to purchase all of the outstanding shares of common stock, par value $0.01 per share, of the Company (the “Shares”) at a purchase price of $24.25 per Share, net to the seller in cash, without interest, and less any applicable withholding taxes, upon the terms and subject to the conditions set forth in the Offer to Purchase, dated March 7, 2011, as amended or supplemented from time to time, and the related Letter of Transmittal.

Except as specifically set forth herein, the Schedule 14D-9 remains unchanged. Capitalized terms used but not defined in this Amendment No. 4 have the meanings ascribed to them in the Schedule 14D-9.

Item 8.  Additional Information.

Item 8 of the Schedule 14D-9 is hereby amended and supplemented by adding the following text as a new paragraph after the last paragraph of section (v) of Item 8:

“On March 23, 2011, the waiting period applicable to the Offer and the Merger under the HSR Act was terminated. Accordingly, the condition of the Offer relating to the expiration or termination of the HSR Act waiting period has been satisfied.”

2

SIGNATURE

After due inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

3