The atomic bombs developed and used during World War II were conservative in design and operation. Weapon designs promising more efficient use of fissile material and larger explosive yields were left on the drawing boards in favor of the simpler Little Boy and Fat Man models. The first postwar test of atomic weapons, Operation Crossroads, did not advance bomb design or performance, but rather the effects of atomic bombs on naval warships. By 1947, a series of events prompted the United States to revisit its nuclear arsenal and plan for the future. Among these events were the overall decision to base national defense on atomic weapons and problems producing significant quantities of fissile material. New weapons were needed to meet evolving national defense requirements. Weapon designs using fissile material more efficiently were necessary to increasing the number of weapons in the stockpile. Operation Sandstone, conducted in the spring of 1948, tested weapon designs that met both of these needs.
As with Operation Crossroads, the United States looked to the Marshall Islands for a test site. The remote atoll of Enewetak, with its relatively large land area and the world's second largest lagoon, seemed ideal. After negotiations with U.S. Naval representatives, the Enewetak people agreed to be relocated to Ujelang Atoll. Immediately thereafter, construction crews began turning Enewetak into the Pacific Proving Ground.
X-Ray, Yoke, and Zebra
Just before sunrise on April 14, 1948, the first of three nuclear devices detonated 200 feet over the sands of Enewetak atoll. Codenamed X-Ray, the sixth nuclear device ever detonated, exploded with a yield of 37 kilotons. The second device, codenamed Yoke, exploded on April 30th with a yield of 49 kilotons. On May 14th, the third and final shot, codenamed Zebra, exploded with a yield of 18 kilotons. All three shots were successful and led directly to the United States improving both the quantity of nuclear weapons in the stockpile as well as increasing the explosive yield of individual devices.
Operation Sandstone had two very important outcomes. First, it improved the defense capabilities of the United States. Since the series was conducted after the massive demobilization of the military and during a time of increasing tensions with the Soviet Union, Sandstone provided a much needed boost to the nation's arsenal. Second, the scientific and technical nature of the tests cemented the role of Los Alamos in designing and developing nuclear weapons. The continued existence of Los Alamos after World War II had been tenuous. Sandstone proved the value of the laboratory to the United States.