Military biodefense in the United States began with the United States Army Medical Unit (USAMU) at Fort Detrick, Maryland, in 1956. (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 disestablished in 1969 and succeeded by today's United States Army Medical Research Institute of Infectious Diseases . Indeed, in the largest biological weapons accident known–the anthrax outbreak in Sverdlovsk in the Soviet Union in 1979, sheep became ill with anthrax as far as 200 kilometers from the release point of the organism from a military facility in the southeastern portion of the city (known as Compound 19 and still off limits to visitors today