Shot HOOD was fired on 5 July 1957. It was lofted by balloon to a height of 1,500-feet over Area 9, about 14 miles southwest of Watertown. The device exploded with a yield of 74 kilotons, the most powerful airburst ever detonated within the continental United States. HOOD's nuclear cloud drifted over Groom Pass and the Papoose Range, depositing fallout on the Groom Lake area and its shock wave damaged a number of buildings at Watertown.
The Groom Lake base had always been intended as a temporary facility. As U-2 testing began to wind down and CIA pilot classes finished training, Watertown became a virtual ghost town. By mid-June 1957, the U-2 test operation had moved to Edwards AFB, California, and the operational U-2 aircraft were assigned to the 4028th Strategic Reconnaissance Squadron at Laughlin, Texas. This was just as well. The airbase was about to be rocked as never before.
HOOD, the sixth nuclear shot of Plumbbob was truly spectacular, and caused substantial damage at Watertown. The device had been designed by the University of California Radiation Laboratory at Livermore, California. It was lofted by balloon to a height of 1,500-feet over Area 9, about 14 miles southwest of Watertown. At 4:40 a.m. on 5 July 1957, HOOD exploded with a yield of 74 kilotons, the most powerful airburst ever detonated within the continental United States. It was five times as powerful as the bomb dropped on Hiroshima, Japan, during World War II.
According to Under The Cloud by Richard Miller, HOOD was a thermonuclear explosive, or hydrogen bomb. It was detonated in spite of an informal agreement between the government and the military precluding the use of fusion weapons on U.S. soil. Miller cites a letter from Col. William McGee of the Defense Nuclear Agency, dated 7 July 1980, which admits that HOOD "was a thermonuclear device and a prototype of some thermonuclear weapons currently in the national stockpile."
HOOD's nuclear cloud drifted over Groom Pass and the Papoose Range, depositing fallout on the Watertown camp where the blast had already left its mark. According to a memorandum from R.A. Gilmore of the Nevada Test Organization's Off-Site Radiation Safety Office, HOOD's shockwave damaged a number of buildings at Watertown. Damage included shattered windows on the west sides of Building 2 and the Mess Hall, a broken ventilator panel on the north side of Dormitory Building 102. Two metal Butler buildings suffered the most severe blast effects. A maintenance building on the west side of the base had its west and east doors buckled, and the south door of the supply warehouse west of the hangars buckled in.