Shot Hood was the seventh nuclear detonation of Operation Plumbbob, fired on 5 July 1957 from a balloon at 457 metres above Area 9a of the Nevada Test Site. At 74 kilotons it was — and remains — the largest atmospheric nuclear test ever conducted on the continental United States. Hood was a UCRL two-stage thermonuclear device, though the US government maintained at the time that no thermonuclear tests were being conducted in Nevada. The device was compact: 30.7 centimetres in diameter, 107 centimetres long, weighing 178 kg — designed to fill a gap in the 135–180 kg thermonuclear warhead range. Approximately 7 kilotons of the overall yield came from fusion. Predicted yield was 60–80 kt. The shot also served as the largest military exercise associated with any single nuclear detonation in the Plumbbob series: 2,500 Marines conducted troop maneuvers in the vicinity, supported by air operations involving 124 aircraft.