Office of the Secretary of Defense OSD

When the National Security Act of 1947 created a Secretary of Defense to oversee the separate military departments, the first Secretary, James Forrestal, had only a small staff and limited authority. Amendments in 1949, 1953, 1958, and 1986 steadily strengthened the Secretary's office, giving it control over budgets, weapons programs, and policy across the services. The Office of the Secretary of Defense is the civilian staff that exercises that control, separate from the uniformed Joint Staff that supports the Chairman of the Joint Chiefs.

OSD is led by the Secretary and the Deputy Secretary, who usually manages the department's day-to-day business and budget. Below them are under secretaries for policy, acquisition and sustainment, research and engineering, personnel and readiness, intelligence and security, and the comptroller, who prepares the defense budget, along with the general counsel and other offices. Many of these positions require Senate confirmation, and together they set strategy, oversee weapons purchases worth hundreds of billions of dollars, and manage a workforce of millions.

Civilian control of the military is exercised largely through OSD, and debates over its size, its relationship with uniformed leaders, and the politicization of defense policy recur across administrations. In 2025 the Secretary ordered substantial cuts to headquarters staff and senior officer positions, and a September 2025 executive order authorized the use of Department of War as a secondary name for the department, changes that supporters described as restoring focus on warfighting and critics described as symbolic or disruptive.