“Big bomb dropped on Hiroshima B August 5 at 7.15 pm Washington time. First reports indicate complete success." Eighty years ago, this laconic message announced to President Harry S Truman and the American people one of the atrocities of the 20th century.

Yet in the years before the war, Truman's predecessor, Franklin D Roosevelt, had appealed to the governments opposing Hitler "publicly to affirm [the] determination ... in no event and under no circumstances[to] undertake bombardment from the air of civilian populations".