February 27
Plutonium separation begins at the Mayak complex near Chelyabinsk begins, dumping highly radioactive waste into the Techa river. Radioactivity from the Techa river is discovered in the Arctic as early as 1951.

March
General Curtis LeMay's first nuclear war plan for the Strategic Air Command envisions attacks on 70 Soviet cities with 133 bombs.

April 4
The North Atlantic Treaty establishes NATO, a military alliance aimed at protecting Western nations from the Soviet bloc.

May 15
Communists win elections in Hungary. 

July
Physicist Edward Teller rejoins the staff at Los Alamos, New Mexico.

July 29
UN Atomic Energy Commission suspends its meetings because of irreconcilable differences between the U.S. and USSR. [see December 30, 1946]

August 29
Soviet Union detonates its first atomic bomb, Joe 1 (10-20 kilotons) at Semipalatinsk in Kazakhstan. 

September 3
U.S. weather plane flying off the coast of Siberia picks up evidence of radioactivity.

September 23
President Truman announces explosion of first Soviet atomic bomb. Text

October
U.S. government expands production of uranium and plutonium.

October 29
General Advisory Committee to the U.S. Atomic Energy Commission argues against a crash program to develop the hydrogen bomb.

November 25
In a letter Atomic Energy Commissioner Lewis Strauss urges President Truman to give highest priority to development of hydrogen bomb. 

December 2 and 3
Hanford Nuclear Plant releases three tons of irradiated uranium fuel in an experiment called Green Run aimed at duplicating pollution from a Soviet reactor. The experiment places more than 7,800 curies of radioactive iodine-131, known to cause thyroid cancer in humans, into the environment. This classified atomic intelligence experiment was not disclosed for almost four decades.