History of the United States 6–3 decision in Korematsu v. United States Supreme Court case. Research and development took flight as well, best seen in the Manhattan Project, a secret effort to harness nuclear fission to produce highly destructive atomic bombs. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the U.S. Army Corps of Engineers. Nuclear physicist J. Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the actual bombs. The first nuclear device ever detonated was an implosion-type bomb at the Trinity test, conducted at New Mexico's Alamogordo Bombing and Gunnery Range on
Mark 18 nuclear bomb placed in the fissile pit to reduce the risk of accidental high yield detonation, and removed during the last steps of the arming sequence. Beginning in March 1953, the United States deployed a number of Mark 18 bombs. A total of 90 were manufactured and placed in service. The weapon had a short lifetime, and was replaced by thermonuclear weapons in the mid-1950s. The Mark 18 weapons were all modified into lower yield Mark 6 nuclear bomb variants in 1956. Mark 18 nuclear bomb The Mark 18 nuclear bomb, also known as the SOB or Super Oralloy Bomb, was an