The Office of the Secretary of Defense (OSD) is a headquarters-level staff of the United States Department of Defense. It is the principal civilian staff element of the U.S. Secretary of Defense, and it assists the Secretary in carrying out authority, direction and control of the Department of Defense in the exercise of policy development, planning, resource management, fiscal, and program evaluation responsibilities. OSD is the Secretary of Defense's support staff for managing the Department of Defense, and it corresponds to what the Executive Office of the President of the U.S. is to the U.S. president for managing the whole of the Executive branch of the federal government.
The United States under secretary of defense for policy (USDP) is a high level civilian official in the United States Department of Defense. The under secretary of defense for policy is the principal staff assistant and adviser to both the secretary of defense and the deputy secretary of defense for all matters concerning the formation of national security and defense policy.
The Assistant Secretary of Defense for Networks & Information Integration (ASD(NII)) was an appointed position that provided management and oversight of all DoD information technology, including national security systems. The ASD(NII) also served as the chief information officer (CIO) of the United States Department of Defense (DoD), a position distinct from the ASD and governed by the Clinger-Cohen Act.
The under secretary of defense for intelligence and security or USD(I&S) is a high-ranking civilian position in the Office of the Secretary of Defense (OSD) within the U.S. Department of Defense (DoD) that acts as the principal civilian advisor and deputy to the secretary of defense (SecDef) and deputy secretary of defense (DepSecDef) on matters relating to military intelligence and security. The under secretary is appointed as a civilian by the president and confirmed by the Senate to serve at the pleasure of the president.
The under secretary of defense for personnel and readiness, or USD (P&R) is a high-ranking civilian position in the Office of the Secretary of Defense (OSD) within the United States Department of Defense responsible for advising the secretary and deputy secretary of defense on recruitment, career development, pay and benefits, and oversight of the state of military readiness. The under secretary is appointed from civilian life by the president and confirmed by the Senate to serve at the pleasure of the President.
The Under Secretary of Defense for Acquisition and Sustainment, or USD (A&S), is the Principal Staff Assistant (PSA) and advisor to the Secretary of Defense for all matters relating to acquisition and sustainment in the Department of Defense. This includes the DoD Acquisition System; system design and development; production; logistics and distribution; installation maintenance, management, and resilience; military construction; procurement of goods and services; material readiness; maintenance; environment and energy resilience ; utilities; business management modernization; International Armaments Cooperation, Cooperative Acquisition and International Agreements, Promoting exportability of military components to allies and partners; nuclear, chemical and biological defense programs; and nuclear command, control, and communications.
The Under Secretary of Defense (Comptroller)/Chief Financial Officer, abbreviated USD(C)/CFO, is a high level civilian official in the United States Department of Defense. The Under Secretary of Defense (Comptroller)/CFO is the principal staff assistant and adviser to both the Secretary of Defense and the Deputy Secretary of Defense for all budgetary and fiscal matters, including the development and execution of the Defense Department's annual budget.
The Assistant Secretary of Defense for Health Affairs (ASD(HA)) is chartered under United States Department of Defense Directive (DoDD) 5136.1 in 1994. This DoDD states that the ASD(HA) is the principal advisor to the U.S. Secretary of Defense on all "DoD health policies, programs and activities." In addition to exercising oversight of all DoD health resources, ASD(HA) serves as director of the Tricare Management Activity.
The Assistant to the Secretary of Defense for Public Affairs, or ATSD (PA), is the principal staff advisor and assistant to the Secretary of Defense and Deputy Secretary of Defense for public information, internal information, community relations, information training, and audiovisual matters in support of Department of Defense activities, leading a worldwide public affairs community of some 3,800 military and civilian personnel. The Assistant to the Secretary follows the Secretary's Principles of Information in providing Defense Department information to the public, the United States Congress and the media.
The Under Secretary of Defense for Research and Engineering, abbreviated USD (R&E), is a senior official of the United States Department of Defense. The USD (R&E) is charged with the development and oversight of technology strategy for the DoD. The post has at various times had the titles Assistant Secretary of Defense for Research and Engineering, or Director of Defense Research and Engineering (DDR&E). The latter title has itself historically varied between the rank of under secretary and that of assistant secretary.
The Assistant Secretary of Defense for Nuclear, Chemical & Biological Defense Programs, or ASD(NCB), is the principal adviser to the Secretary of Defense, Deputy Secretary of Defense and the Under Secretary of Defense for Acquisition and Sustainment on policy and plans for nuclear, chemical, and biological defense programs.
The Assistant Secretary of Defense for Indo-Pacific Security Affairs, or ASD (IPSA), is the principal advisor to the Under Secretary of Defense for Policy (USD(P)) and the Secretary of Defense on international security strategy and policy on issues of DoD interest that relate to the governments and defense establishments of the nations and international organizations within the Indo-Pacific region. It primarily includes the entire region from India to Japan, and the region where ASEAN is located. The position was originally titled Assistant Secretary of Defense for Asian and Pacific Security Affairs but was renamed by the first Trump Administration alongside the renaming of the United States Indo-Pacific Command.
The Assistant Secretary of Defense for Readiness and Force Management, or ASD(R&FM), is a Defense Department position responsible for civilian and military personnel policy, readiness of the force, military community and family policy and diversity management and equal opportunity.
The Assistant Secretary of Defense for Sustainment (ASD (Sustainment)), formerly known as the Assistant Secretary of Defense for Logistics and Materiel Readiness (ASD(L&MR)), is one of three assistant secretaries reporting to the Under Secretary of Defense for Acquisition and Sustainment. Formerly the position was an adviser to the Under Secretary of Defense for Acquisition, Technology and Logistics, Deputy Secretary of Defense, and Secretary of Defense on logistics and materiel readiness issues within the Department of Defense (DoD), including programs related to logistics, materiel readiness, maintenance, strategic mobility, and sustainment support. As the principal logistics official within the senior management of the DoD, the ASD(Sustainment) exercises authority, direction and control over the director of the Defense Logistics Agency. Like all other Assistant Secretaries of Defense, the ASD(Sustainment) is considered a part of the Office of the Secretary of Defense.
The Assistant Secretary of Defense for Energy, Installations, and Environment, concurrently the Chief Sustainability Officer, and formerly known as the Deputy Under Secretary of Defense for Installations and Environment, provides management and oversight of military installations worldwide and manages environmental, safety, and occupational health programs for the Department of Defense (DoD). DoD's installations cover some 29,000,000 acres (120,000 km2), with 539,000 buildings and structures valued at more than $700 billion. The responsibilities of the ASD(EI&E) include the development of installation capabilities, programs, and budgets; installation-energy programs and policy; base realignment and closure; privatization of military housing and utilities; and integration of environmental needs into the weapons acquisition process. The ASD(EI&E) is also responsible for environmental management, safety and occupational health; environmental restoration at active and closing bases; conservation of natural and cultural resources; pollution prevention; environmental research and technology; fire protection; and explosives safety. The ASD(EI&E) reports to the Under Secretary of Defense for Acquisition and Sustainment, and is a part of the Office of the Secretary of Defense.
Assistant Secretary of Defense is a title used for many high-level executive positions in the Office of the Secretary of Defense within the U.S. Department of Defense. The Assistant Secretary of Defense title is junior to Under Secretary of Defense. Reorganization Plan No. 6 of 30 June 1953 increased the number of assistant secretaries. The National Defense Authorization Act for Fiscal Year 2023 added three new Assistant Secretary positions under the Under Secretary for Research and Engineering. The list of Assistant Secretaries of Defense includes:
Tina Susan Kaidanow was an American diplomat and government official. She served as the Acting Assistant Secretary of State for Political-Military Affairs before moving to the United States Department of Defense. From 2008 to 2009, Kaidanow served as United States Ambassador to Kosovo.
William Jordan Gillis is an American government official. He has served as Assistant Secretary of Defense for Sustainment since March 2020. He previously served as Principal Deputy Assistant Secretary of the Army for Installations, Energy and Environment, and earlier as the Acting Assistant Secretary of the Army for Installations, Energy and Environment from October 16, 2017, until January 10, 2019.
John Daniel Caine is a retired United States Air Force lieutenant general who served as the associate director for military affairs of the Central Intelligence Agency from 2021 to 2024. He served as the director of Special Access Program Central Office of the Office of the Under Secretary of Defense for Acquisition and Sustainment from 2019 to 2021. Previously, he was the deputy commanding general of the Special Operations Joint Task Force – Operation Inherent Resolve.
Gary A. Ashworth is an American retired Lieutenant Colonel who has served as the acting United States Secretary of the Air Force since January 2025.
