In 1952, the United Kingdom became the third nation to possess nuclear weapons when it detonated an atomic bomb in Operation Hurricane on October 3, 1952, which had a yield of 25 kilotons. Despite major contributions to the Manhattan Project by both Canadian and British governments, the U.S. Congress passed the Atomic Energy Act of 1946, which prohibited multi-national cooperation on nuclear projects. The Atomic Energy Act fueled resentment from British scientists and Winston Churchill, as they believed that there were agreements regarding post-war sharing of nuclear technology, and led to Britain developing its own nuclear weapons. Britain did not begin planning the development of their own nuclear weapon until January 1947. Because of Britain's small size, they decided to test their bomb on the Montebello Islands, off the coast of Australia. Following this successful test, under the leadership of Churchill, Britain decided to develop and test a hydrogen bomb. The first successful hydrogen bomb test occurred on November 8, 1957, which had a yield of 1.8 megatons. An amendment to the Atomic Energy Act in 1958 allowed nuclear cooperation once again, and British-U.S. nuclear programs resumed. During the Cold War, British nuclear deterrence came from submarines and nuclear-armed aircraft. The "Resolution"-class ballistic missile submarines armed with the American-built Polaris missile provided the sea deterrent, while aircraft such as the Avro Vulcan, SEPECAT Jaguar, Panavia Tornado and several other Royal Air Force strike aircraft carrying WE.177 gravity bomb provided the air deterrent.