Truman tells Stalin about the bomb

On 24 July 1945, after the afternoon plenary session at Cecilienhof Palace had ended, the President of the United States, Harry Truman, walked round the conference table to Joseph Stalin. Without his own interpreter, relying on the Soviet one, he told him – “casually”, as he himself recorded in his memoirs – that the United States had a new weapon of unusual destructive force. Stalin, according to Truman’s account, showed no special interest: he replied only that he was glad to hear it and hoped the Americans would make “good use of it against the Japanese”. The conversation lasted a few moments, and not a word was said about the weapon being atomic.

War chronologies sum up the episode by saying that Truman “hinted” that the United States had nuclear weapons. This is a simplification on two counts. Truman did not use the words “atomic” or “nuclear” – he spoke of a “new weapon”, deliberately avoiding detail. Nor did the United States yet have a ready arsenal: it had the result of one successful test, carried out eight days earlier, and two bombs in preparation, the first of which could be ready at the beginning of August.

News from New Mexico

The Potsdam Conference had been under way since 17 July, and its opening came the day after the Trinity test – the first detonation of a nuclear device, carried out at dawn on 16 July in the New Mexico desert. Secretary of War Henry Stimson, who had come to Potsdam as the government’s overseer of the Manhattan Project, received that same evening a coded cable from Washington about the successful “operation”, and on 18 July a second, more optimistic one. The full report by General Leslie Groves, describing the power of the explosion, the fireball and the destruction of the steel tower, was brought by courier on 21 July. Stimson read it to Truman and to Secretary of State James Byrnes.

According to Stimson’s diary, the President was tremendously buoyed up by the report. Winston Churchill, who read Groves’s report himself on 22 July, told Stimson – as Stimson noted – that already the day before he had been struck by the change in Truman’s behaviour: the President had stood up to the Russians firmly and confidently. According to American accounts Churchill also remarked that, beside the new weapon, gunpowder and electricity were nothing, and that the atomic bomb was “the Second Coming in Wrath”. For the British the news carried particular weight – under the agreement reached in 1943 at the Quebec Conference, the United States could not use the bomb without Britain’s consent; that consent was formally given at a meeting of the Combined Policy Committee in Washington on 4 July 1945.

Tell him, but not too much

The Americans had been weighing for weeks whether to tell Stalin anything, and if so what. The Interim Committee, set up by Stimson in May 1945 to deal with atomic weapons, recommended on 21 June that the President should inform Stalin at the forthcoming conference that the United States was working on a new weapon and intended to use it against Japan – without giving details. It was argued that keeping completely silent and then suddenly using the bomb would undermine Moscow’s trust and destroy the chances of later international control of atomic energy. Some of the scientists in the programme Groves had headed since 1942 gave similar warnings – especially those at the Chicago laboratory, authors of James Franck’s June report – convinced that using the bomb without prior agreement with the other powers would unleash an arms race. Among them was Leó Szilárd, the man who in 1939 had persuaded Albert Einstein to write a letter to the President. Byrnes was sceptical and preferred to keep the advantage as long as possible.

Truman and Churchill discussed the matter on 18 July and agreed that the President would tell Stalin about the new weapon after one of the sessions, briefly and without going into technical detail. The form was carefully considered: the mention would protect the Americans from the charge that they had hidden the bomb from an ally, while giving Stalin no reason to hasten his entry into the war against Japan or to demand a share in the secret. Churchill watched the scene from a few metres away. In his memoirs he wrote that he was sure Stalin had no idea of the significance of what he had been told, and that when he asked Truman afterwards how it had gone, the President replied that Stalin had not asked a single question. Byrnes and the American diplomat Charles Bohlen remembered the moment in similar terms.

Stalin knew more than they thought

Stalin’s composure did not stem from incomprehension. Soviet intelligence had been penetrating the Western atomic programme for years. The physicist Klaus Fuchs, a member of the British mission at Los Alamos, had passed on in June 1945, through the courier Harry Gold, a description of the design of the plutonium bomb and the information that it would be tested in July and that the weapon was to be used against Japan. Independently of him, the young American physicist Theodore Hall had been supplying data on the implosion method since the autumn of 1944. Reports from these sources went to the People’s Commissar for State Security, Vsevolod Merkulov, and to Lavrentiy Beria, who supervised Soviet atomic work on behalf of the leadership. According to documents released after 1991, Moscow knew the approximate date of the test even before 16 July.

The Soviet Union had been running its own nuclear programme since 1943 under the physicist Igor Kurchatov, but on a modest scale: uranium was scarce and the war consumed most resources. Stalin therefore had reason to react indifferently to Truman’s news – and not to give away how much he knew.

The reaction in the Soviet quarters

What happened after the conversation is known from later memoirs of Soviet participants in the conference, which must be read with caution. Marshal Georgy Zhukov wrote that on returning to his residence Stalin described his talk with Truman in the presence of Vyacheslav Molotov. Molotov is said to have remarked that the Americans were “raising their price”, and Stalin, laughing, to have replied that they must talk to Kurchatov that very day about speeding up the work. The then ambassador in Washington, Andrei Gromyko, recalled for his part that Stalin regarded the mention as an attempt at pressure and was convinced that Washington and London were counting on a long monopoly – which, he added, they would not manage to keep.

Historians, among them David Holloway in his study of Stalin and the bomb, point out that the real turning point in the Soviet programme came not at Potsdam but after the destruction of Hiroshima. Only on 20 August 1945 did the State Defence Committee set up a Special Committee chaired by Beria, which turned scattered research into an undertaking of state priority. The conversation of 24 July nonetheless confirmed Stalin in his belief that the Americans meant to use the bomb as an argument against Moscow as well.

The decisions of the following days

Truman’s mention was not a prelude to negotiation but accompanied decisions already taken. That same morning Stimson had persuaded the President to strike Kyoto, the old capital and centre of Japanese culture, from the target list. On 25 July the acting Army Chief of Staff, General Thomas Handy – with the approval of Stimson and of the Chief of Staff George Marshall, both in Potsdam – issued an order to the commander of the US Strategic Air Forces in the Pacific, General Carl Spaatz: the 509th Composite Group was to drop its first “special bomb” as soon as the weather permitted after about 3 August, on one of the targets Hiroshima, Kokura, Niigata or Nagasaki. The components of the Little Boy bomb were by then already on their way to Tinian.

A day later the Potsdam Declaration was issued, calling on Japan to surrender unconditionally under threat of “prompt and utter destruction”, though without a word about the new weapon. The Soviet Union, which formally remained neutral towards Japan, was not asked to sign it. On 6 August the bomb fell on Hiroshima, on 8 August the USSR declared war on Japan, and on 9 August a second bomb destroyed Nagasaki.

The start of a race

The brief conversation at Cecilienhof became one of the symbols of the passage from wartime alliance to great-power rivalry. Some historians – the so-called revisionist school goes furthest here – believe that Truman’s decisions were already influenced by a wish to demonstrate American power to the Soviet Union; others stress that the main aim was to end the war with Japan quickly, and that the USSR was a secondary consideration. Whatever the verdict, the plan to forewarn Stalin while revealing nothing proved pointless: Stalin knew more about the bomb than Truman supposed, and the Americans did not know how much he knew.

The monopoly proved shorter than Washington had assumed. On 29 August 1949 the Soviet Union detonated its first nuclear device, RDS-1, at the test site near Semipalatinsk; it was modelled to a large extent on the American plutonium bomb whose description Fuchs had passed on. An arms race began that would shape the Cold War for decades to come.