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.

The typical role of the deputy secretary of defense is to oversee the day-to-day business and lead the internal management processes of the $500-billion-plus Department of Defense budget, that is as its chief operating officer; while the secretary of defense as the chief executive officer focuses on the big issues of the day, ongoing military operations, high-profile congressional hearings, attending meetings of the National Security Council, and directly advising the president on defense issues.

[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).