In Donald Maclean’s British Foreign Policy Since Suez 1956-1968 he discusses Britain’s relationship with Europe and the United States. He charts the changing fortunes of Britain and the history of the uneasy straddling of Europe and the United States that Britain has been pursuing since the Second World War.
Part of that relationship concerns the dropping of the atomic bombs on Japan.
I knew that the pursuit of a viable weapon was a joint British and US effort. I thought, though, that the decision to drop the bombs rested solely with the USA.
What I learned from Maclean’s book was that there was an agreement between Britain and the United States that the bomb would only be used with the consent and agreement of both countries. In plain English, Britain gave approval to the use of the atomic bombs dropped on Hiroshima and Nagasaki.
I found a 2013 article in Japan Times which said that according to papers recently declassified by the U.S. National Archives and Records Administration, Britain supported the use of atomic bombs by the United States against Japan in World War II and did so about a month before the first one was dropped on Hiroshima.
This corroborates what Maclean wrote. On page 53 of British Foreign Policy Since Suez 1956-1968 he writes:
The presence of U.S. nuclear bases on U.K. soil and other aspects of the Anglo-American alliance exposes Britain to the risk of nuclear counter-attack should the United States use nuclear weapons against the Soviet Union. This remains true whether the US. fires its first salvo from British bases, from a Polaris submarine in mid-Atlantic from the United States or from some other quarter.
For an official account of the conclusion of this agreement, and its text, see Margaret Gowing, Britain and Atomic Energy 1939-1945. London. 1964. pp. 164-171
From the point of view of the British sponsors of the alliance, the logic of this situation requires that there should be a binding overall agreement that the United States will not in any circumstances use nuclear weapons against the Soviet Union without British consent. Washington has not been willing to tie its hands in this way, but, besides the guarantees relating specifically to the use of bases in Britain, gave unofficial assurances of a wider character.
At the earliest stage of Anglo-American co-operation in nuclear matters—during the manufacture of the first, wartime, atomic bombs—such a binding agreement existed and was applied. From the signing of the Quebec Agreement by Roosevelt and Churchill in August 1943 until its disavowal by the Truman Administration at the end of the war, both countries had a clear-cut obligation, set out in the second clause of the Agreement, not to use nuclear weapons against third parties without each other’s consent. This clause was strictly complied with before the American atomic attack on Hiroshima.
The hiatus was subsequently partially filled by personal assurances from the President to the Prime Minister, given orally and requiring renewal with each change of President.