The Potsdam Conference was held near Berlin on 17 July 1945, the day after the Trinity test, and was to run until 2 August. The conference was for the ‘Big Three’ heads of state – Joseph Stalin (USSR), Winston Churchill (UK) and Harry S. Truman (America) – to discuss how to administer Germany after their surrender in World War II. Clement Attlee (UK) as Deputy Prime Minister, also participated alongside Churchill while awaiting the outcome of the 1945 United Kingdom general election.
Nuclear weapons weren’t part of the conference discussions, but during a break Truman mentioned a “powerful new weapon” to Stalin. Stalin told Truman to “make good use of this new addition to the Allied arsenal”. Truman was surprised, he had been expecting Stalin to ask questions. He was unaware Stalin already knew of the Trinity test and nuclear developments in the US because his Soviet spies within the Manhattan Project had been passing information for some time. Relationships were straining between the leaders. These were the early stages of the Cold War.
Stalin, Truman and Churchill during the Potsdam Conference
Towards the end of the conference on 26 July, Truman, Churchill and the Chairman of the Nationalist Government of China issued the Potsdam Declaration. This document outlined the terms of surrender for the Empire of Japan and stated that the ‘alternative for Japan is prompt and utter destruction’. The Soviets were not part of the ultimatum because they had not yet declared war on Japan.
At a press conference with the Japanese press in Tokyo, Prime Minister Suzuki was pushed to say something on Japan’s decision. As no decision had been reached Suzuki stated that the Japanese policy would be one of “mokusatsu” – withholding comment or no comment.
Translators interpreted the word as ‘treat with silent contempt’ or ‘kill with silence’. The US believed this to be a ‘rejection by ignoring’. The translation led to a decision by the White House to carry out the threat of ‘prompt and utter destruction’.
Avro Lancaster’s 33 ft. bomb-bay
The Manhattan project first considered which aircraft could carry an atomic bomb in 1943. The size of the 17-foot ‘Thin Man’, which was under development at the time, reduced the options of Allied aircraft that could deliver the bomb. Only the Avro Lancaster with its 33 ft. bomb-bay and the American Boeing B-29 Superfortress were considered. The Lancaster would have required much less modification, but would have required additional crew training for the United States Army Air Force (USAAF) crews, and Major General Leslie R. Groves Jr., the director of the Manhattan Project, thought it was ‘beyond comprehension to use a British plane to deliver an American A-bomb’.
Boeing B-29 Superfortress
The bomb was to be dropped by the B-29 Boeing Superfortress. The aircraft required substantial modification to be able to carry the atomic bomb. ‘Silverplate’ was the codename for the B-29 modification project. The four 12-foot bomb-bay doors and the fuselage section between the bays were removed and a single 33 ft. bomb-bay was configured to accommodate the ‘Thin Man’ and ‘Fat Man’. The ‘Silverplate’ codename eventually became the word that identified the training and operational details of the program as well.
In July 1944, the ‘Thin Man’ was shelved and all work on a gun-type fission weapon focussed on ‘Little Boy’. It was a development and simplification of the ‘Thin Man’. The barrel length of ‘Little Boy’ was less than 10 ft. and able to fit in a standard B-29 bomb-bay. ‘Silverplate’ worked with this new configuration on the B-29s. ‘Fat Man’, (implosion-type weapon) and ‘Little Boy’ (gun-type weapon) would be the bombs to drop on Japan.
Lieutenant Colonel Paul Tibbets, an officer with a distinguished combat record in Europe and North Africa, was selected to form and train a group to deliver atomic bombs. Tibbets was a test pilot for the B-29s so had expert knowledge of the aircraft. In September 1944 he chose Wendover Airforce Base in Utah as the location for the training program. The base was given the code name ‘Kingman’, and it became the Manhattan Project’s Site K.
March 1945 – Project Alberta, also known as Project A, was formed. It was a section of the Manhattan Project, and its task was to plan and implement the steps needed to drop the atomic bombs on Japan. ‘Silverplate’ now came under the influence of Project Alberta.
Project Alberta consisted of 51 US Army, Navy, and civilian personnel, including William Penney the British scientist. Penney had worked on means to assess the effects of a nuclear explosion, and wrote a paper on what height the bombs should be detonated at for maximum effect in the attacks on Japan.
General Leslie Groves considered William Penney indispensable to the project and Penney was chosen to be a member of the committee to select Japanese cities for atomic bombing.
The Target Committee met in Washington on 27 April 1945, with follow-up meetings at Los Alamos on 10 May and in Washington on 29 May.
The committee nominated five possible targets base on the following criteria:
- they be important targets in a large urban area of more than three miles diameter
- they be capable of being damaged effectively by a blast
- they are likely to be un-attacked by next August. Dr. Stearns had a list of five targets which the Air Forces would be willing to reserve for our use unless unforeseen circumstances arise.
The list was: Kyoto, the former capital of Japan; Hiroshima, an important army depot and port of embarkation in the middle of an urban industrial area; Yokohama, an important urban industrial area for aircraft manufacture, machine tools, docks, electrical equipment and oil refineries that has so far been untouched; Kokura Arsenal, one of the largest arsenals in Japan and is surrounded by urban industrial structures; Niigata, a port of embarkation on the N.W. coast of Honshu, and its importance is increasing as other ports are damaged.
The US Secretary of War, Henry L. Stimson, raised his concerns for the bombing of Kyoto with President Truman. From 1927 to 1929 Stimson had served as Governor-General of the Philippines. He had honeymooned at the city of Kyoto and loved it. He requested that the city be removed from the target list due to its historical, religious and cultural significance. His diary records that he told the President his reason was “because I did not want to have the United States get the reputation of outdoing Hitler in atrocities”.
Truman’s diary entry of the same meeting reads, “This weapon is to be used against Japan between now and August 10th. I have told the Sec. of War, Mr. Stimson, to use it so that military objectives and soldiers and sailors are the target and not women and children. Even if the Japs are savages, ruthless, merciless and fanatic, we as the leader of the world for the common welfare cannot drop that terrible bomb on the old capital or the new.
He and I are in accord. The target will be a purely military one and we will issue a warning statement asking the Japs to surrender and save lives. I’m sure they will not do that, but we will have given them the chance. It is certainly a good thing for the world that Hitler’s crowd or Stalin’s did not discover this atomic bomb. It seems to be the most terrible thing ever discovered, but it can be made the most useful.”
Nagasaki was added to the list in place of Kyoto.
4 July 1945 – A meeting of the Combined Policy Committee was held at the Pentagon, to discuss the use of the bombs. The Quebec agreement stipulated that ‘neither country would use them against other countries without consent’.
The British scientist James Chadwick, who was the head of the British team working on the Manhattan Project and discoverer of the neutron, was present at the meeting. At the meeting Field Marshal Sir Henry Maitland Wilson announced that the British government concurred with the use of nuclear weapons against Japan. This was officially recorded as a decision of the Combined Policy Committee.
At Wendover, prototype atomic weapons (without nuclear materials) were constructed for drop testing. The tests were to learn the flight characteristics of the two bomb designs. The Flight Test Section of the USAAF carried out 24 drop tests in June and 30 in July. Majority of the tests were with the ‘Fat Man’ type.
Although all of its components had been tested in target and drop tests, no full test of ‘Little Boy’ occurred before its use on Hiroshima. The main reason was there was insufficient uranium-235. Additionally, the weapon design was simpler and the gun-type design was considered almost certain to work.
Each bombardier on the B-29 crew completed at least 50 practice drops before Tibbets declared his group combat-ready. By the 29 May 1945, the group had officially changed station from Wendover to North Field, on Tinian in the Mariana Islands. It was from there that the atomic bombings would be carried out.
‘Little boy’ about to be loaded into Enola Gay
The first aircraft to drop an atomic bomb was the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets. The primary target was to be Hiroshima, with alternative targets of Kokura and Nagasaki.
The B-29 aircraft, which had not yet been named Enola Gay, flew to Tinian on 6 July. During that month it made eight practice flights and flew two missions, dropping conventional bombs on industrial cities of Kobe and Nagoya in Japan. On 31 July the aircraft made a rehearsal flight for the Hiroshima mission.
5 August 1945 – Tibbets assumed command of the aircraft and named it after his mother, Enola Gay Tibbets. The now famous nose art was painted on the aircraft that day.
Colonel Paul Tibbets, pilot of the Enola Gay, waving from its cockpit.
Photograph taken by 509th Photographer Pfc Armen Shamlian
6 August 1945 – The Enola Gay took off from Tinian for the six hour flight to Japan, accompanied by two other B-29s – The Great Artiste and Necessary Evil. The support aircraft were carrying instrumentation and were to take photos.
The Enola Gay arrived over the target in clear visibility and released the bomb at 08:15 Japanese time. ‘Little Boy’ took 53 seconds to fall to detonation height. The detonation created a blast of approximately 15 kilotons of TNT and the radius of destruction was about one mile. The blast caused fires across over four square miles.
Only Tibbets, and two others on the crew knew of the nature of the weapon. The others on the bomber were only told to expect a blinding flash and given black goggles. “It was hard to believe what we saw”, Tibbets later told reporters, while another crew member said “the whole thing was tremendous and awe-inspiring … the men aboard with me gasped ‘My God'”.
General Carl Spaatz decorates Colonel Paul W, Tibbets with the Distinguished Service Cross after the Hiroshima mission
Enola Gay and the supporting B-29s returned safely to Tinian. Tibbets was presented with the, the Distinguished Service Cross, the USAAF’s second highest military award, as he disembarked the aircraft.
This was the first nuclear weapon used in warfare, dropped only three weeks after the Trinity test at Alamogorado in the New Mexico desert.
Tibbets was given responsibility for the timing of the second bombing. It was scheduled for 11 August, but moved two days earlier to avoid a forecast period of bad weather forecast. The implosion-type ‘Fat Man’ bomb was to be used on the mission to bomb Kokora, and would be dropped by the B-29 Superfortress Bockscar.
Bockscar nose art: the ‘Fat Man’ silhouettes represent four pumpkin bomb missions (black) and the atomic bomb drop on Nagasaki (a red symbol, fourth in the line of five symbols)
Bockscar was named after the aircraft’s command pilot – Captain Frederick C. Bock. The B-29 arrived at Tinian on 16 June and was used in 13 training and practice missions, and three combat missions in which it dropped conventional bombs on industrial targets in Japan. For the Kokora mission Major Charles W. Sweeney would pilot the aircraft and Bock and his crew were flying the support aircraft, The Great Artiste.
The Great Artiste was designated as the observation and instrumentation aircraft. Big Stink was also a support aircraft on the mission and tasked with photographing the explosion and effects of the bomb. Big Stink was carrying scientific observers, including William Penney.
9 August 1945 – Enola Gay, flown by Captain George Marquardt, was the weather reconnaissance aircraft for the mission. Enola Gay reported clear skies over Kokura.
Before the mission, Tibbets had told Sweeney to take no more than fifteen minutes at the rendezvous before proceeding to the target. Bockscar reached the rendezvous point and assembled with The Great Artiste. After circling for some time, The Big Stink failed to appear. Although he was ordered not to wait longer than fifteen minutes, Sweeney continued to wait for The Big Stink. Now half an hour behind time, the two aircraft could wait no longer and proceeded to Kokura.
Mission map for the bombings missions on 6 and 9 August, 1945
An issue with an American physicist forgetting his parachute delayed take-off for Big Stink. The aircraft failed to make its rendezvous with the remainder of the strike flight.
By the time Bockscar arrived, clouds and drifting smoke obscured the aiming point. The smoke was from fires started by the conventional bombing of Yahata by B-29s the day before. After three unsuccessful passes Bockscar diverted to its secondary target, Nagasaki.
Bockscar dropped the ‘Fat Man’ on Nagasaki at 10:58 Japanese time. It exploded 43 seconds later with a blast yield equivalent to 21 kilotons of TNT.
Atomic cloud over Nagasaki from B-29 Big Stink
Big Stink arrived at Nagasaki in time to photograph the effects of the blast, although it was at the higher altitude of 39,000 ft. rather than the planned 30,000 ft. Penney saw the Nagasaki detonation from the air at a distance. As the leading expert on the effects of nuclear weapons, Penney was a member of the team of scientists and military analysts who later entered Hiroshima and Nagasaki to assess the effects of nuclear weapons.
Atomic bombing of Japan (L) Hiroshima, (R) Nagasaki
The ‘Fat Man’ was more powerful than ‘Little Boy’, but the damage and the number of victims at Nagasaki was much lower. The centre of the blast at Nagasaki lay in a small valley so a major portion of the city was protected, while Hiroshima was on flat terrain.
An hour before midnight on 8 August 1945 Stalin declared war on Japan and the Soviet forces invaded after midnight on 9 August. The Soviet invasion helped to defeat Japan’s Kwantung Army and brought about the Japanese surrender and the termination of World War II.
15 August 1945 – Japan surrendered to the Allies, six days after the Soviet Union’s declaration of war and the bombing of Nagasaki. The Japanese government signed the instrument of surrender on 2 September in Tokyo Bay, which effectively ended World War II.
The two bombings, which killed at least an estimated 135,000 people, remain the only use of nuclear weapons for warfare in history. The bombings have been credited with shortening the war and sparing many more lives.