the 1949 Amendments to the National Security Act of 1947, changed the title to deputy secretary of defense.

Former assistant to President Franklin D. Roosevelt, Stephen Early, became the first officer holder when he was sworn in on May 2, 1949.

Public Law 95-140, October 21, 1977, established two Under Secretaries of Defense and abolished the second deputy position.

[4] The deputy secretary, among the office's many responsibilities, chairs the Senior Level Review Group (SLRG), before 2005 known as Defense Resources Board (DRB), which provides department-wide budgetary allocation recommendations to the Secretary and the President.

Traditionally, the deputy secretary has been the civilian official guiding the process of the Quadrennial Defense Review (QDR).