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nuclear weapons
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1933
September
12
Szilard and the chain reaction
On 12 September 1933 in London the Hungarian physicist Leó Szilárd conceived the idea of a nuclear chain reaction, later the basis of work on the atomic bomb.
1939
January
25
Uranium fission at Columbia University
On 25 January 1939 physicists at Columbia University in New York carried out the first experiment in America confirming the fission of the uranium nucleus.
August
02
Einstein's letter to Roosevelt
The letter of 2 August 1939, written by Leó Szilárd and signed by Einstein, warned Roosevelt that Germany might build an atomic bomb.
1941
June
21
The creation of the Office of Scientific Research and Development
In late June 1941 Roosevelt created Vannevar Bush’s OSRD, which took over US military research, from radar to uranium. The Manhattan Project began in 1942.
1942
June
18
The Manhattan Project begins
On 18 June 1942 Colonel James C. Marshall was ordered to organise the military side of the American atomic programme. So the Manhattan Project was born.
September
04
Groves takes over the Manhattan Project
In September 1942 Colonel Leslie Groves took charge of the US atomic programme. Within days he secured uranium, a site in Tennessee and top priority.
December
02
Key event
The first controlled chain reaction
On 2 December 1942, beneath the stands of Stagg Field in Chicago, Enrico Fermi's team started up Chicago Pile-1 – the first nuclear reactor.
1943
February
28
Operation Gunnerside
During the night of 27–28 February 1943 Norwegian SOE commandos blew up the heavy water plant at Vemork. Not a shot was fired, and all evaded pursuit.
July
23
The B-36 bomber ordered
On 23 July 1943 the US Army Air Forces ordered 100 six-engined B-36 bombers by letter of intent, before the first prototype had even flown.
August
19
The Quebec Conference and the Quebec Agreement
On 19 August 1943 in Quebec Churchill and Roosevelt signed a secret agreement on jointly building the atomic bomb. The conference also confirmed Overlord.
November
16
The raid on Vemork
On 16 November 1943 American bombers attacked the Vemork power station and heavy water plant and the works at Rjukan. More than 20 Norwegians were killed.
1945
March
10
Fu-Go balloons over Hanford
On 10 March 1945 a Japanese Fu-Go balloon fell on a high-voltage line in Washington State, briefly shutting down the Hanford plutonium reactors.
July
16
Key event
The Trinity test
At 5.29 a.m. on 16 July 1945, in the Jornada del Muerto desert in New Mexico, the Americans detonated the “Gadget” – the first nuclear device in history.
24
Truman tells Stalin about the bomb
On 24 July 1945 at Potsdam Truman mentioned to Stalin a new weapon of unusual destructive force. Stalin, forewarned by his intelligence, took it calmly.
30
The sinking of the “Indianapolis”
On 30 July 1945 the Japanese submarine I-58 sank the cruiser Indianapolis, which had delivered atomic bomb parts to Tinian. 316 of 1,195 men survived.
August
06
Key event
The atomic bombing of Hiroshima
At 8.15 a.m. on 6 August 1945 the B-29 Enola Gay dropped the uranium bomb Little Boy on Hiroshima – the first nuclear weapon used in war.
09
Key event
The atomic bombing of Nagasaki
On 9 August 1945 the B-29 Bockscar dropped the plutonium bomb Fat Man on Nagasaki. Estimates put the deaths by the end of the year at 40,000–74,000.
15
Key event
Hirohito's broadcast
At noon on 15 August 1945 radio aired Hirohito's recorded address accepting the Potsdam Declaration. The Japanese first heard their Emperor's voice.