One hundred above-ground nuclear tests were conducted at the Nevada Test Site (NTS) between January 27, 1951, and July 17, 1962. On August 5, 1963, the Soviet Union and the United States signed the Limited Test Ban Treaty (LTBT), which prohibited nuclear tests in the atmosphere, under water, and in space. From that time, until the end of testing in 1992, nuclear tests at the NTS were conducted underground. However, these post-LBTB tests were not the first underground nuclear events at the NTS.