Sputnik crisis
The United States terminated co-operation after the war ended with the Atomic Energy Act of 1946. This prompted the United Kingdom to relaunch its own project, High Explosive Research. Production facilities were established and British scientists continued their work under the auspices of an independent British programme. Finally, in 1952, Britain performed a nuclear test under codename "Operation Hurricane". In 1958, in the wake of the Sputnik crisis and the British demonstration of a two-stage thermonuclear bomb, the United Kingdom and the United States signed US–UK Mutual Defence Agreement, which resulted in a resumption of Britain's nuclear Special Relationship with the United States.