1948

The Military and Political Consequences of Atomic Energy by P. M. S. Blackett argues that the United Kingdom cannot achieve an independent nuclear deterrent. As a result, the government blacklists Blackett for over a decade.

January 7

U.S. and Great Britain revoke wartime pact on nuclear cooperation. 

February 25

Soviet forces occupy Prague, capital city of Czechoslovakia.

March 13

British physicist Klaus Fuchs delivers "classical super" design for the construction of the hydrogen bomb to his agent, Alexander Feklisov .

April

U.S. Atomic Energy Commission begins Operation Sandstone at Eniwetok Atoll in the Pacific to test the improved designs of fission bombs.

May 5

Joint Chiefs of Staff brief President Truman on "Halfmoon," their nuclear war plan. The plan calls for dropping 50 atomic bombs on 20 Russian cities. Truman disapproves. 

June

Soviet physicist Igor Tamm enlists his graduate student Andrei Sakharov to study fusion problem.

June 7

Reactor A at the Mayak complex near Chelyabinsk reaches full criticality, enabling the USSR to produce plutonium.

June 19

First Soviet plutonium production reactor becomes operational at Kyshtym in the Ural Mountains.

June 24

USSR blocks rail and road connections to West Berlin.

July

Soviet physicist Andrei Sakharov begins development of "Layer Cake" concept for hydrogen bomb.

October 19

General Curtis LeMay assumes command of the U.S. Strategic Air Command.