1950 

Senator Brien McMahon (Connecticut) calls for an "all-out" nuclear weapons program.

January 27
In London British physicist Klaus Fuchs confesses to being a Soviet spy.

January 31
President Harry Truman announces that United States Atomic Energy Commission will proceed with work " on all forms of atomic weapons, including the so-called hydrogen or super-bombs ." The development of the bomb is led by physicist Edward Teller , who believes it is vital for the United States to develop the hydrogen bomb before the Soviet Union does.

February
Joint Intelligence Committee predicts build up of Soviet atomic arsenal and possible attack against U.S. "at earliest possible moment."

February 5
Twelve leading U.S. physicists, including Hans Bethe , speak out against President Truman 's decision to build the hydrogen bomb.

February 24
U.S. Joint Chiefs of Staff request "all out effort to build H-bomb."

March 1
In the United Kingdom, physicist Klaus Fuchs is sentenced to 14 years for betraying atomic secrets to Soviet agents; the evidence is used later to incriminate Julius and Ethel Rosenberg , who were condemned to death. 

April 7
National Security Council releases document NSC-68 that warns of surprise attack by Soviet Union once "it has sufficient atomic capability."

April 11
A B-29 Bomber carrying a nuclear bomb crashes into a mountain near Kirtland Air Force Base in New Mexico. The bomb is destroyed but the accompanying nuclear capsule, which had not been inserted into the bomb, remains intact. 

June 16
Calculations by U.S. mathematicians Stanislaw Ulam and Cornelius Everett appear to prove that Edward Teller 's "classical super" design for hydrogen bomb does not work.

June 25
North Korea invades South Korea.

September 30
NSC-68 becomes cornerstone of U.S. foreign policy and defense spending is increased by more than 350%. 

November 30
During press conference, President Truman confirms that U.S. government considered using nuclear weapons in Korea. 

December
First production of electricity from atomic fission occurs at the National Reactor Testing Station in Idaho. 

December 9
General Douglas MacArthur requests discretionary authority to use atomic weapons during the Korean War.