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

German physicist Klaus Fuchs confesses to being a Soviet spy to British intelligence officials.

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.

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

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

The United Kingdom physicist Klaus Fuchs is sentenced to fourteen years in prison for betraying atomic secrets to Soviet agents; the evidence is later used to incriminate Julius and Ethel Rosenberg, who were both condemned to death.

The National Security Council releases document NSC-68, which warns of a surprise attack by the Soviet Union once "it has sufficient atomic capability."

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.

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

North Korea invades South Korea.

NSC-68 becomes the cornerstone of U.S. foreign policy, and defense spending is increased by more than 350 percent.

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

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

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