Shortly after the testing groups were disestablished, the testing ban was lifted briefly when the Soviet Union detonated a nuclear device in the atmosphere in September 1961. A flurry of full-scale U.S. test activity resulted during 1961 and 1962. These tests were part of the National Nuclear Test Readiness Program, which had been set up as a direct response to President John F. Kennedy’s Safeguard C, which required readiness to promptly resume atmospheric testing should the need arise. Atmospheric testing of nuclear weapons finally ended with the 1963 Limited Test Ban Treaty.