January 27 - Klaus Fuchs confesses that he gave atomic secrets to the Soviets while working at the Manhattan Project. January 31 - President Truman announces the decision to proceed with development of the hydrogen bomb.
January 27 - The first nuclear test occurs at the Nevada Test Site. June - First British nuclear reactor goes critical. Julius and Ethel Rosenberg are convicted and sentenced to death for passing information on atomic weapons to the U.S.S.R.
September - A second U.S. nuclear weapons laboratory is established in Livermore, California. October 3 - First British atomic bomb, "Hurricane," was tested at Monte Bello Islands, Australia, with a yield of 25 kilotons. October 31 - U.S. explodes first thermonuclear or fusion device, "Mike," at Eniwetok Atoll. It had a yield of 10.4 megatons.
August 12 - First Soviet layer cake design bomb explods on a tower in Siberia. It was not a "true" hydrogen bomb.
March 1 - The first deliverable hydrogen bomb design is tested at Bikini Atoll. "BRAVO" has a yield of 14.8 megatons. Radioactive fallout affects local islanders and a nearby fishing boat. April 12 to May 6 - Hearings regarding Oppenheimer's loyalty cause him to lose his security clearance. September 30 - The USS Nautilus, the first American nuclear powered submarine, is launched.
The U.S.S.R. deploys two strategic bombers, Bear and Bison. The United Kingdom announces the decision to develop thermonuclear weapons. November 22 - The first true fusion device test is acheived by the Soviet Union; it has a yield of 1.6 megatons. The development is lead by Andrei Sakharov.
May 15 - First British H-bomb exploded at Christmas Island. The yield was between 200 - 300 kilotons. It was less than expected. July 29 - The United Nations International Atomic Energy Agency is created. The agency inspects nuclear reactors and plants to ensure they are being run for peaceful purposes. August 26 - The Soviet Union announces the successful launch of an intercontinental ballistic missile. September 19 - First underground nuclear test, "Rainier," occurs at the Nevada Test Site. It had a yield of 1.7 kilotons. November 8 - Britain's first truly successful thermonuclear bomb test. The bomb had a yield of 1.8 megatons. October - Fire destroys the core of a reactor at Britain's Windscale nuclear complex, sending clouds of radioactivity into the atmosphere.
July 2 - President Eisenhower signs amendments to the 1954 U.S. Atomic Energy Act which opened the way to a bilateral agreement between Britain and America on nuclear weapon design information. November 1958 to September 1961 - U.S., U.K., and U.S.S.R. observe an informal moratorium on nuclear tests.
June 9 - The first U.S. Polaris nuclear missile-capable submarine enters into service. October 31 - The U.S. deploys the first operational intercontinental ballistic missile (ICBM), the Atlas D.