Defense Threat Reduction Agency

The Defense Threat Reduction Agency (DTRA) is both a defense agency and a combat support agency within the United States Department of Defense (DoD) for countering weapons of mass destruction (WMD; chemical, biological, radiological, nuclear, and high explosives) and supporting the nuclear enterprise. Its stated mission is to provide "cross-cutting solutions to enable the Department of Defense, the United States Government, and international partners to Deter strategic attack against the United States and its allies; Prevent, reduce, and counter WMD and emerging threats; and Prevail against WMD-armed adversaries in crisis and conflict." DTRA is headquartered in Fort Belvoir, Virginia. The DTRA mission, organization and management, responsibilities and functions, relationships, authorities, and administration are defined in DoD Directive 5105.62, Defense Threat Reduction Agency (DTRA).

DTRA was officially established on 1 October 1998, as a result of the 1997 Defense Reform Initiative by consolidating several DoD organizations, including the Defense Special Weapons Agency (successor to the Defense Nuclear Agency) and the On-Site Inspection Agency. The Defense Technology Security Administration and the Nunn–Lugar Cooperative Threat Reduction program office in the Office of the Secretary of Defense were also incorporated into the new agency.

In 2002, DTRA published a detailed history of its predecessor agencies, Defense's Nuclear Agency, 1947–1997, the first paragraph of which makes a brief statement about the agencies which led up to the formation of DTRA:

Defense's Nuclear Agency, 1947–1997, traces the development of the Armed Forces Special Weapons Project (AFSWP), and its descendant government organizations, from its original founding in 1947 to 1997. After the disestablishment of the Manhattan Engineering District (MED) in 1947, AFSWP was formed to provide military training in nuclear weapons' operations. Over the years, its sequential descendant organizations have been the Defense Atomic Support Agency (DASA) from 1959 to 1971, the Defense Nuclear Agency (DNA) from 1971 to 1996, and the Defense Special Weapons Agency (DSWA) from 1996 to 1998. In 1998, DSWA, the On-Site Inspection Agency, the Defense Technology Security Administration, and selected elements of the Office of Secretary of Defense were combined to form the Defense Threat Reduction Agency (DTRA).

DTRA employs approximately 1,400 DoD civilians and 800 uniformed service members at more than a dozen permanent locations worldwide. Most personnel are at DTRA headquarters at Fort Belvoir. Approximately 15% of the workforce is split between Kirtland Air Force Base and the White Sands Missile Range in New Mexico, and the Nevada National Security Site (formerly the Nevada Test Site), where they test and support the U.S. military's nuclear mission. The remaining 15% of the workforce is stationed in Germany, Kazakhstan, Azerbaijan, Uzbekistan, Georgia, Ukraine, Armenia, Kenya, South Korea, Japan, and Singapore. DTRA also has liaisons with the U.S. military's Combatant Commands, the National Guard Bureau, the FBI and other U.S. government interagency partners.

In 2005, the United States Strategic Command (USSTRATCOM) was designated as the lead Combatant Command for the integration and synchronization of DoD's efforts in support of the government's "Combating WMD" objectives. It was at this time that the SCC-WMD was co-located with DTRA. The Combat Command designation was changed again in 2017 when responsibility was moved to U.S. Special Operations Command (USSOCOM).

In 2012, the Standing Joint Force Headquarters for Elimination (SJFHQ-E) was relocated to the DTRA/SCC-WMD headquarters at Fort Belvoir. This centralized the DoD's Combating Weapons of Mass Destruction operations, a move recommended in the 2010 Quadrennial Defense Review.

On 30 September 2016, the Joint Improvised-Threat Defeat Agency (JIDA) became part of DTRA and was renamed the Joint Improvised-Threat Defeat Organization (JIDO) in accordance with the 2016 National Defense Authorization Act (NDAA). In Section 1532 of the NDAA, Congress directed the DoD to move JIDA to a military department or under an existing defense agency.