Shot Fox was the fifth and final nuclear detonation of Operation Ranger, fired on 6 February 1951 as an airburst at 437 metres above Frenchman Flat, Nevada. The device — codenamed Freddy — produced 22 kilotons against a predicted yield of 34 kt. Operation Ranger was the first nuclear test series conducted in the continental United States since Trinity in 1945, and the first ever at what would become the Nevada Test Site. It was proposed during technical discussions at Los Alamos in December 1950, received Presidential approval on 11 January 1951, and the first shot was fired just 16 days later. All five shots of the series were completed in eight days. The operation was driven by two urgent pressures: the outbreak of the Korean War in June 1950 had raised fears that access to the Pacific Proving Ground at Enewetak could be cut off, and weapons designers had concluded that systematic data on fission weapon parameters was urgently needed before the upcoming Operation Greenhouse tests. The intensifying nuclear competition with the Soviet Union — which had conducted its first atomic test in 1949 — gave the entire programme its strategic urgency.