The Office of the Secretary of Defense (OSD) is responsible for policy development, planning, resource management, and program evaluation. The secretary of defense oversees the Defense Department and acts as the principal defense policymaker and adviser. OSD includes the offices of top civilian defense decision-makers in personnel, weapons acquisition, research, intelligence, and fiscal policy. President-elect Trump has nominated Pete Hegseth for this role, but he has yet to be confirmed by the Senate. (Source: Defense.gov)