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Blog Topic: Pumpkin Bombs
Training/Practice for Atomic Bombing Missions

April 12, 2015

Pumpkin test bomb for 1945 atomic bomb missions at Wendover Air Field

Pumpkin training bomb for the Hiroshima Atomic bombing mission (Little Boy version) - filled with concrete. Sign says: World War II B-29 training bomb, 1945. Display at Wendover Air Field, where initial training took place for the atomic bombing missions of 1945.

The early training/test bombs for the 1945 atomic bomb missions were designed to be the same shape, size, and weight of the atomic bombs (Little Boy and Fat Man).1 These bombs were called pumpkins and were used at Wendover Air Field for the initial bombing training/practice by the Silverplate2 B-29s, and to test fuses for the atomic bombs.

The pumpkins were not actually atom bombs, but facsimiles that looked just like them in size, shape, and had the same fuses, and aerodynamic properties. They were filled with the requisite amount of cement for the correct weight, and were used by the Silverplate B-29s on test runs.

During the training time at Wendover Airfield, the military also planned to use the pumpkins to test atom bomb fuses which were to detonate at 1,800 feet. To test this, a small amount of explosives would be used to make a white puff of smoke, letting the observers know when the fuse had actually detonated.

However, a problem arose when the ground crew tried to load the first pumpkin bomb into the B-29 bomb bay. Although the bay had been altered to hold a large atomic bomb, at five feet in diameter, the Fat Man facsimile was larger than the clearance between the open bomb bay and the tarmac. So it just would not fit beneath the plane to allow it to be loaded.

Charles Sweeney discussed this issue with the ground crew and the weapons engineer and they finally concluded that the only thing they could do at the moment was raise the nose and slip the bomb under the front of the B-29. A new base at the time, Wendover, really didn't have the cranes needed to lift up the front end of a plane, so the crew threw tarps over each of the rear horizontal stabilizers on the B-29, and put several men (six to eight), pulling down on each tarp. The strength of these men tipped the tail of the B-29 down, which lifted the nose up in the air, providing the clearance for the ground crew to slip the pumpkin below the bomb bay. (The length of the plane pivoted on the main wheels like a seesaw). When they set the nose back down again, they lifted the bomb into the bay and secured it to the aircraft.3, 4

Army engineers found a long term solution to bomb loading by designing and building bomb pits. However, the ground crew had to keep using this tipping method for bomb loading of the B-29s for two months before the bomb pits were completed. Then the crew could lower the bomb into the pit using hydraulics, back the B-29 over the pit, and with the hydraulics, lift the bomb up into the bomb bay. Wendover Air Field ended up with three separate bomb pits. There was another pit built at Tinian, and then a fifth pit was constructed on Iwo Jima for the Hiroshima mission.

When the 509th composite group5 got to Tinian, they continued to use pumpkins, but now, instead of cement contents, the pumpkin bombs contained five to ten thousand pounds of explosives, and the practice runs used Japanese held islands and the mainland as targets.

The pumpkin bomb was actually the biggest bomb in the Pacific theater, although this was not true for Europe, where the British developed two large conventional bombs, Tall Boy and Grand Slam, for bombing German submarine pens.

So that gets to the next issue. If the B-29 could not have been modified to take the atom bombs, the plane that was waiting in the wings to do the job was the British Avro Lancaster which had already been modified to take the Tall Boy bombs. They literally cut the bomb bay away, and made the fuselage half as thick for these special Lancaster bombers. Modified Lancasters were already available and in use prior to the atomic bomb missions, but everyone in the U.S. Army Air Force from Hap Arnold on down, were adamant about dropping the atom bomb from an American bomber. And so this whole Silverplate2 issue came to pass, modifying B-29s to carry atom bombs rather than using a modified Lancaster.

~ Jon

1 The atomic bombs Little Boy, and Fat Man were dropped respectively on Hiroshima on August 6, and Nagasaki, on August 9 of 1945.
2 Silverplate is a reference to the B-29 bombers which were modified to carry an atomic bomb.
3 Charles Sweeney, War's End. New York: Avon Books, 1997. Sweeney was the pilot in the B-29, Bock's Car, which dropped the atomic bomb on Nagasaki.
4 In my reading, I have come across another time a crew used the weighting down of the rear stabilizers to lift the front end of the aircraft. In that case, P-38 Lightning crews needed work on the front landing gear for maintenance, particularly in the Pacific, which tended to lack adequate maintenance facilities.The P-38 has twin booms and a single stabilizer, which connects those two booms in the rear. But when they needed to work on the front end of the P-38, on the landing gear in particular, men sat on the back end of the stabilizer, in enough numbers that their weight tipped the back end of the Lightning down and front end up. At that point the crew could perform the necessary maintenance. So it's an interesting concept to use this technique to solve an access problem, and although not a very common technique, it was one that worked.
5 The 509th composite group carried out the atomic bombing missions on Japan.


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