Pumpkin bomb
A pumpkin bomb
Type	Conventionalhigh-explosive bomb Ballistic simulator
Place of origin	United States
Service history
In service	1945
Used by	United States Army Air Forces
Wars	World War II
Production history
No. built	486
Specifications
Mass	5.26 long tons (5.34 t)
Length	10 feet 8 inches (3.25 m)
Diameter	60 inches (152 cm)
Filling	Composition B
Filling weight	6,300 pounds (2,900 kg)

Pumpkin bombs were conventional aerial bombs developed by theManhattan Project and used by the United States Army Air Forces against Japan duringWorld War II. Its physical characteristics closely replicated those of theFat Manplutonium bomb, with the same ballistic and handling characteristics, but it used non-nuclear conventionalhigh explosives. It was mainly used for testing and training purposes, which included combat missions flown with pumpkin bombs by the509th Composite Group. The name "pumpkin bomb" was the term used in official documents from the large, fat ellipsoidal shape of the munition casing instead of the more usual cylindrical shape of other bombs, required to enclose the Fat Man's spherical "physics package" (theplutonium implosion nuclear weapon core).

Pumpkin bombs were a means of providing realistic training with non-nuclear bombs for the509th Composite Group'sBoeing B-29 Superfortress crews assigned to drop theatomic bomb. The pumpkin bomb had a similar size and weight distribution as aFat Man plutonium bomb, giving it the sameballistic and handling characteristics.^[1] Specifications for the bomb required that it be carried in the forwardbomb bay of aSilverplate (nuclear-enabled) B-29 bomber and befuzed to be effective against actual targets.^[2]

Pumpkin bombs were produced in both inert and high-explosive variants. The inert versions were filled with a cement-plaster-sand mixture that was combined with water to 1.67 to 1.68 grams per cubic centimetre (0.060 to 0.061 lb/cu in), the density of theComposition B high-explosive versions. The filler of both variants had the same weight and weight distribution as the inner spherical "physics package" of the Fat Man plutonium bomb.

The concept for the high-explosive pumpkin bomb was originated in December 1944 byUnited States NavyCaptainWilliam S. Parsons, the head of the Ordnance Division atManhattan Project'sLos Alamos Laboratory, andUnited States Army Air ForcesLieutenant ColonelPaul W. Tibbets, commander of the 509th Composite Group. Prior testing was carried out with an inert version.^[1]

The name "pumpkin bomb" originated with Parsons and Dr.Charles C. Lauritsen of theCalifornia Institute of Technology, who managed the development team.^[2] The name was used for the training bombs in official meetings and documents,^[3] and probably derived from its largeellipsoidal shape. On the other hand, anecdotal sources attribute the naming of the bombs to apumpkin color: While the bombs were painted olive drab or khaki in the field, photographs show that at least the units delivered toTinian were shipped in the same yellowzinc chromate primer color worn by Fat Man.^[4][5]

While many Manhattan scientists expected that the development of the means of delivery of the atomic bomb would be straightforward, Parsons, with his experience of theproximity fuze program, expected that it would involve considerable effort.^[6] The test program was initiated on 13 August 1943 at theNaval Proving Ground inDahlgren, Virginia, where a scale model of the Fat Man plutonium bomb was developed. On 3 March 1944, testing moved toMuroc Army Air Field, California. Initial tests found that the Fat Man assembly was unstable in flight, and that its fuzes did not work properly.^[6]

The shells of the pumpkin bomb were manufactured by twoLos Angeles firms,Consolidated Steel Corporation andWestern Pipe and Steel Company, while the 'California Parachute' tail assembly was produced byCenterline Company ofDetroit. After initial development, management of the program was turned over to the U.S. NavyBureau of Ordnance in May 1945.^[2] A total of 486 live and inert training bombs were eventually delivered, at a cost of betweenUS$1,000 and $2,000 apiece.^[1]

All of the inert versions went from the manufacturers directly toWendover Army Air Field, Utah, by rail, where they were used by the 216th Base Unit in flight testing of the bomb. Some test drop missions were flown by the 509th Composite Group's393d Bombardment Squadron as training exercises.^[1] The bombs intended as live ordnance were shipped to the Naval Ammunition Depot,McAlester, Oklahoma, for filling with explosives. The Composition B was poured as aslurry, solidified in a drying facility for 36 hours, sealed, and shipped by railroad to thePort Chicago Naval Magazine, California, for shipment by sea to Tinian.^[1][3]

The pumpkin bombs were externally similar to the Fat Man bomb in size and shape, and both had the same 52-inch (130 cm) California Parachute square tail assembly and single-point attachment lug. The pumpkin bomb had threecontact fuzes arranged in anequilateral triangle around the nose of the bomb, while the atomic bomb had four fuse housings. The atomic bomb had its shell sections bolted together and sealed with externally-applied, sprayed-on liquid asphalt, but most if not all of the pumpkin bombs were welded, with a four-inch hole used for filling the shell. The Fat Man also had four external mounting points forradarantennas which the pumpkin bombs did not have.^[1][4]

The pumpkin bombs were 10 feet 8 inches (3.25 m) in length and 60 inches (152 cm) in maximum diameter. They weighed 5.26 long tons (5,340 kg), consisting of 3,800 pounds (1,700 kg) for the shell, 425 pounds (193 kg) for the tail assembly, and 6,300 pounds (2,900 kg) of Composition B filler. The shells were made of .375-inch (9.5 mm)steel plate and the tail assemblies from .200-inch (5.1 mm)aluminumplate.^[1]

Combat missions were flown by the 509th Composite Group on 20, 23, 26 and 29 July and 8 and 14 August 1945, using the bombs against individual targets in Japanese cities. A total of 49 bombs were dropped on 14 targets, one bomb was jettisoned into the ocean, and two were aboard aircraft that aborted their missions.^[7]

Mission parameters and protocols were similar to those of the actual atomic bomb missions, and all targets were located in the vicinity of the cities designated for atomic attack. The bombs were released at an altitude of 30,000 feet (9,100 m) and the aircraft then went into the sharp turn required on a nuclear mission. After the war, theStrategic Bombing Survey concluded that the pumpkin bombs were "a reasonably effective weapon against Japanese plants when direct hits were scored on vital areas, or when the near miss was sufficiently close to important buildings to cause severe structural damage."^[8]

• Campbell, Richard H. (2005).The Silverplate Bombers: A History and Registry of the Enola Gay and Other B-29s Configured to Carry Atomic Bombs. Jefferson, North Carolina: McFarland & Company.ISBN 0-7864-2139-8.OCLC 58554961.
• Coster-Mullen, John (2012).Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man. (self published).OCLC 298514167.
• Hoddeson, Lillian; Henriksen, Paul W.; Meade, Roger A.;Westfall, Catherine L. (1993).Critical Assembly: A Technical History of Los Alamos During the Oppenheimer Years, 1943–1945. New York City: Cambridge University Press.ISBN 0-521-44132-3.OCLC 26764320.

• World War II aerial bombs of the United States
• History of the Manhattan Project
• Atomic bombings of Hiroshima and Nagasaki
• Nuclear warfare

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