Dugway Proving Ground is part of the Utah Test and Training Range, the nation's “largest overland contiguous block of supersonic authorized restricted airspace,” with over 19,000 square miles of restricted airspace and 2,675 square miles of ground space. Dugway is used primarily by the Army and the Air Force for chemical and biological weapons testing; it covers 801,505 acres of western Utah land. Since its inception in 1942, there have been thousands of tests involving at least 35 different chemical or biological agents, in addition to items listed as “undisclosed agents” and “unknown agents.” The vast majority of these are silent and invisible: they look and sound like nothing.