Project Cloud Gap: Demonstrated Destruction of Nuclear Weapons was a program run by the United States Department of Defense and the Arms Control and Disarmament Agency from 1963 to 1967 (or 1969, according to other sources) whose purpose was to "test the technical feasibility of potential arms control and disarmament measures". Arms control agreements discussed between the United States and the Soviet Union would involve on-site inspections, and such techniques, which involved giant drilling rigs and helicopter overflights to detect secret underground testing, were field-tested by Cloud Gap. The program was abandoned after a helicopter crash during a mock inspection exercise killed several team members.