Question: Bruce Edwards Ivins worked at Fort Detrick which hosted most elements of what?
Context: Frank Rudolph Olson (July 17, 1910 – November 28, 1953) was an American bacteriologist, biological warfare scientist, and Central Intelligence Agency (CIA) employee who worked at Camp Detrick (now Fort Detrick) in Maryland.  In rural Maryland, he was covertly dosed with LSD by his CIA supervisor and, nine days later, plunged to his death from the window of a New York City hotel room.  Some — including the U.S. government — term his death a suicide, while others allege murder. Major Fredrick Louis Detrick, MD (April 21, 1889 in New Market, Maryland – June 3, 1931 in Baltimore, Maryland), was a U.S. Army physician, flight surgeon and pilot.  He is the namesake of Fort Detrick, Maryland (formerly, Detrick Field and Camp Detrick).  Detrick, who was a teaching surgeon on the faculty of the Johns Hopkins University Hospital, Baltimore, served in France during the First World War and was a member of the Maryland National Guard when he died of a heart attack in 1931. Bruce Edwards Ivins (April 22, 1946 – July 29, 2008) was an American microbiologist, vaccinologist, senior biodefense researcher at the United States Army Medical Research Institute of Infectious Diseases (USAMRIID), Fort Detrick, Maryland, and the key suspect in the 2001 anthrax attacks. The 1108th Signal Brigade is a United States Army unit responsible for running much of the Raven Rock Mountain Complex and providing strategic communication support to the White House and the Joint Chiefs of Staff.  It was based at Fort Ritchie, but was recommended to be transferred to Fort Detrick, Maryland during the 1995 Base Realignment and Closure. Fort Detrick is a United States Army Medical Command installation located in Frederick, Maryland.  Historically, Fort Detrick was the center of the US biological weapons program from 1943 to 1969.  Since the discontinuation of that program, it has hosted most elements of the United States biological defense program. The United States Army Medical Unit (1956–1969) — a now defunct medical research unit for biodefense — was at Fort Detrick, Maryland, USA.  In contrast to the U.S. Army Biological Warfare Laboratories (1943–1969), also at Fort Detrick, the USAMU's mission was purely to develop defensive measures against bio-agents, as opposed to weapons development.  The USAMU was the predecessor to today's USAMRIID. Building 470 — also called the Pilot Plant, or sometimes “the Tower”, or “Anthrax Tower” — was a seven-story steel and brick building at Fort Detrick in Frederick, Maryland, USA, used in the small-scale production of biological warfare (BW) agents.  The building, a Cold War era structure, was transferred from the Department of Defense to the National Cancer Institute-Frederick (a unit of the National Institutes of Health) in 1988, to which it belonged until 2003 when it was demolished. The Nallin Farm Springhouse and Bank Barn are closely associated with the Nallin Farm House on the grounds of Fort Detrick, Maryland, USA.  The barn is a good example of a fieldstone-built bank barn with a byre on the lower level and an earth ramp on the opposite side providing access to a haymow. The War Research Service (WRS) was a civilian agency of the United States government established during World War II to pursue research relating to biological warfare.  Established in May 1942 by Secretary of War Henry L. Stimson, the WRS was embedded in the Federal Security Agency, the federal agency that administered Social Security and other New Deal programs in the administration of President Franklin D. Roosevelt.  Headed by George W. Merck, president of the Merck & Co. pharmaceutical firm, the WRS was headquartered at Fort Detrick, Maryland. The One-Million-Liter Test Sphere — also known as the Test Sphere, the Horton Test Sphere, the Cloud Study Chamber, Building 527, and the “Eight Ball” (or “8-ball”) — is a decommissioned biological warfare (BW) chamber and testing facility located on Fort Detrick, Maryland, USA.  It was constructed and utilized by the U.S. Army Biological Warfare Laboratories as part of its BW research program from 1951 to 1969.  It is the largest aerobiology chamber ever constructed and was placed on the National Register of Historic Places in 1977.
Answer: United States biological defense program