The Atomic Bomb

Last revised July 27, 2000

The B-29 is perhaps best remembered today as the aircraft which delivered the atomic bombs which destroyed the cities of Hiroshima and Nagasaki, bringing the war in the Pacific to an end.

The idea for the explosive release of nuclear energy by means of an uncontrollable chain reaction was basically due to the Hungarian theoretical physicist Leo Szilard. He seems to have come up with the idea during a sudden inspiration he had while crossing a London street on September 12, 1933.

Alarmed at German progress in nuclear fission research, a group of scientists persuaded Albert Einstein to write a letter to President Franklin Roosevelt to warn him that a weapon of unprecedented power was now within the realm of possibility. Alarmed that the Germans might come up with the bomb first, the United States secretely began a massive bomb development program named the Manhattan Project.

In his letter to President Roosevelt on August 2, 1939, suggesting that an atomic bomb be developed, Albert Einstein feared that the bomb might very well prove too heavy for transport by air. However, estimates indicated that the weapon was well within the capacity of the B-29, which in September of 1943 was selected as its carrier. At first, the team responsible for the adaptation of the B-29 to the atomic bomb would only be provided with rough dimensions of the bomb, since even the scientists were not yet sure what it would look like. The technicians fitted a new H-frame hoist, carrier assembly and release unit to the B-29.

The first drop tests using dummy bombs were carried out at Muroc, California on February 28, 1944. These lead to the fitting of an entirely new suspension mechanism to the B-29. Tests resumed in June of 1944 and after modifications were made a contract was awarded to a firm in Omaha, Nebraska to produced three more modified B-29s. By August, the Omaha firm had completed a total of 46 nuclear-capable B-29s.

The atomic bomb program had followed two separate tracks. One was the development of isotope separation techniques to produce large samples of uranium enriched in the fissionable U235 isotope. The other was the development of techniques for the large-scale production of the artificially-produced element plutonium. The uranium bomb was known as Little Boy and was 120 inches long, 28 inches in diameter, and weighed about 9000 pounds. It was essentially a long cannon with a U235 bullet and three U235 target rings fitted to its muzzle. The chain reaction was initiated by explosively forcing U235 bullet and target together. The plutonium bomb was known as Fat Man and was 60 inches in diameter 128 inches long, and weighed about 10,000 pounds. It had a plutonium shell with an array of shaped charges wrapped around it. When these shaped charges were simultaneously fired, the plutonium was forced violently inward and compressed, starting the chain reaction.

A special crew training program had been initiated under the command of Colonel Paul W. Tibbets, Jr. Col. Tibbets was a veteran of B-17 operations in Europe and North Africa and had been involved in B-29 flight test operations. In September 1944, Colonel Tibbets took over the command of the newly-activated 509th Composite Group at an air base near Wendover, Utah. It had only one Bombardment Squadron--the 393rd commanded by Major Charles W. Sweeney. The 509th Composite Group was a completely self-sufficient unit, with its own engineer, material, and troop squadrons as well as its own military police unit. Since the Manhattan project was carried out in an atmosphere of high secrecy, the vast majority of the officers and men of the 509th Composite Group were completely ignorant of its intended mission.

The 509th CG was deployed overseas in the spring of 1945. The 509th was formally a part of XXI Bombardment Command based in the Marianas. By July, the bombers were established at North Field on Tinian, which had just been completed for the 313th Bombardment Wing. Some of them were fitted with Curtiss electric propellers which had reversible pitch to reduce the landing run and carried special blade cuffs to increase the flow of cooling air into the R-3350 engines.

The first test of an atomic bomb took place on July 16, 1945 at Alamogordo in the New Mexico desert. The news was immediately given to President Harry Truman, who was at the time at the Allied conference at Potsdam. He immediately informed Winston Churchill and Chiang kai-Shek of the success, but told Stalin only that the United States had developed a new and powerful weapon for use against Japan. However, Soviet agents in the USA had already passed the word to the USSR about the Manhattan Project, and Stalin was fully aware of what was going on. On July 26, the Allies issued a joint declaration which called for the unconditional surrender of Japan, indicating that the only alternative was prompt and utter destruction. Exactly what this meant was not specified, The fate of the Emperor was also left ambiguous, and was not mentioned in the declaration.

President Truman was fully aware of the projections of appalling American casualties should it be necessary to invade Japan (a half-million casualties were estimated), and had no hesitation in authorizing the use of the new weapon in getting the Japanese to surrender. On July 24, a directive was sent to General Carl A. Spaatz ordering the 509th to deliver its first atomic bomb as soon as weather would permit. The cities of Hiroshima, Kokura, Niigata and Nagasaki were potential targets. Truman gave his final go-ahead from Potsdam on July 31.

The cruiser Indianapolis had delivered the Little Boy guns and bullet assembly to Tinian on July 26. C-54s delivered the three separate pieces of the Little Boy target assembly, and other C-54s delivered Fat Man's initiator and plutonium core. Three B-29s left Kirtland, each carrying a Fat Man high-explosive preassembly. These did not arrive until August 2.

Little Boy was ready for delivery by July 31. On August 2, LeMay's staff specified Hiroshima as the primary target, with Kokura and Nagasaki as alternates. Hiroshima was chosen because intelligence reports had indicated that there were no Allied POW camps located there.

The raid was set for August 6, and Col Tibbets was to command the attacking B-29. On the day before the mission, his plane (a Martin-Omaha-built B-29-45-MO serial number 44-86292) had been painted with the name Enola Gay, after his mother.

The attack began with a flight of three special reconnaissance F-13As which took off to report the weather over the primary and secondary targets. Col. Tibbets followed in Enola Gay an hour later, accompanied by two other B-29s which would observe the drop. While on the way to Japan, Major Claude Eatherly, flying Straight Flush, radioed that Hiroshima was clear for a visual bomb drop. Navy weapons expert Captain William Parsons armed the bomb while in flight, as it was deemed too dangerous to do this on the ground at North Field, lest an accident happen and the bomb go off, wiping out the entire base.

At 8:15AM, the Enola Gay released Little Boy from an altitude of 31,500 feet. The radar fuse on the bomb had been preset to go off at an altitude of 2000 feet above the ground. In the ensuing explosion, 75,000 people were killed and 48,000 buildings were destroyed.

President Truman announced the dropping of the atomic bomb to the nation. At first, the Japanese did not know exactly what had happened, and poor communications between Tokyo and the devastated Hiroshima did not help. Even in spite of the bomb, there were still some Japanese officers who wanted the war to continue on to the bitter end. On August 8, Foreign Minister Shigenori Togo informed the Emperor that total destruction awaited Japan if it did not accept the terms of the Potsdam Declaration and surrender. The Emperor agreed with this gloomy assessment and Togo dispatched the Emperor's message to the Prime Minister, Baron Kantaro Suzuki, who was unable to convene the Supreme War council until the next day.

While the Japanese government was debating its options, there was no letup with the conventional B-29 raids. B-29s from the 58th, 73rd, and 313th BWs hit the Toyokawa Arsenal the next day. On the night of August 7, the 525th BG dropped 189 tons of mines on several different targets. On August 8, the 58th, 73rd, and 313th BWs dropped incendiary bombs on targets at Yawata in the southern island of Kyushu. At the same time, the 314th BW hit an industrial area of Tokyo. The Japanese defenses were still effective enough to down four B-29s during the Yawata raid and three at Tokyo.

In the meantime, since there was still no official reaction from Japan, the Americans felt that there was no alternative but to prepare a second atomic attack. The plutonium bomb "Fat Man" was loaded into a B-29 known as Bockscar (Martin-Omaha built B-29-35-MO serial number 44-27297, the name often misspelled as Bock's Car), named after its commander, Capt. Frederick C. Bock. However, on this mission, the aircraft was flown by Major Sweeney, with Capt. Bock flying one of the observation planes. The primary target was to be Kokura Arsenal, with Nagasaki as the alternative.

Bockscar took off on August 9, with Fat Man on board. This time, the primary target of Kokura was obscured by dense smoke left over from the earlier B-29 raid on nearby Yawata, and the bombardier could not pinpoint the specified aiming point despite three separate runs. So Sweeney turned to the secondary target, Nagasaki. There were clouds over Nagasaki as well, and a couple of runs over the target had to be made before the bombardier could find an opening in the clouds. At 11:00 AM, Fat Man was released from the aircraft and the bomb exploded. The yield was estimated at 22 kilotons. Approximately 35,000 people died at Nagasaki in the immediate blast.

After releasing the bomb, Sweeney was forced to divert to Okinawa because of a problem with a fuel transfer pump. He borrowed some fuel and returned to Tinian.

That very same day, the Soviet Union had declared war on Japan, and launched a massive invasion of Manchuria. The Emperor ordered that the government accept the Allied terms of surrender at once. It took time for the full details to be worked out, and there was a very real danger that some elements of the Japanese military would still not accept surrender and would attempt a coup even against the Emperor. In the meantime conventional bombing of Japanese targets still continued, with a record number of 804 B-29s hitting targets in Japan on August 14. On the morning of August 15, the Emperor broadcasted word of Japan's surrender in a address to his nation. Most of his subjects had never heard his voice before.

All further offensive operations against Japan ceased after the Emperor's broadcast. After that time, most of the B-29s in the Pacific were diverted to missions of mercy, dropping food and clothing to thousands of Allied prisoners of war held in Japan, China, Manchuria, and Korea. 1066 B-29s participated in 900 missions to 154 camps. Some 63,500 prisoners were provided with 4470 tons of supplies These flights cost eight B-29s lost with 77 crew members aboard.

The surrender was formally signed on September 2 aboard the battleship Missouri, bringing the Pacific War to an end.

After it was retired from service, the Enola Gay was donated to the Smithsonian Institution. For many years, it was held in storage at the Paul Garber Restoration Facility at Suitland, Maryland. In recent years, it has undergone a significant restoration effort so that it could be displayed in public to celebrate the 50th anniversary of the dropping of the first atomic bomb. However, a bitter political controversy developed around the exact details of how the display was to be carried out. As it turned out, only the fuselage of the aircraft was actually displayed.

Bockscar is on display at the USAF Museum at Wright-Patterson AFB in Dayton, Ohio.


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