Boltzmann was a XW-40 light weight boosted fission warhead (12 kiloton shot) fired from a 500 foot tower in the Nevada Test Site May 28, 1957. The shot cab held 9 tons of sand, and 15 tons of paraffin as instrument shielding. Operation Plumbbob was a series of nuclear tests conducted between May 28 and October 7, 1957, at the Nevada Test Site. It was the biggest, longest, and most controversial test series in the continental US. The operation consisted of 29 explosions, of which only two did not produce any nuclear yield. While most Operation Plumbbob tests contributed to the development of warheads for intercontinental and intermediate range missiles, they also tested air defense and anti-submarine warheads with smaller yields. They included 43 military effects tests on civil and military structures, radiation and bio-medical studies, and aircraft structural tests. Approximately 18,000 members of the US Air Force, Army, Navy and Marines participated in exercises Desert Rock VII and VIII during Operation Plumbbob. The military was interested in knowing how the average foot-soldier would stand up, physically and psychologically, to the rigors of the tactical nuclear battlefield.