Pumpkin bomb Pumpkin bombs were conventional high explosive aerial bomb s developed by the Manhattan Project and used by the United States Army Air Forces against Japan during World War II . The pumpkin bomb was a close but non - nuclear replication of the Fat Man plutonium bomb with the same ballistic and handling characteristics . It was mainly used for testing and training purposes , but combat missions were also flown with pumpkin bombs by the 509th Composite Group . The name " pumpkin bomb " resulted from the large ellipsoid al shape of the munition and was the actual reference term used in official documents . Development . The concept for the pumpkin bomb originated in December 1944 by U . S . Navy Captain William S . Parsons , the head of the Ordnance Division at Manhattan Project ' s Los Alamos Laboratory , and United States Army Air Forces Lieutenant Colonel Paul W . Tibbets , the commander of the 509th Composite Group , the unit responsible for delivering the atomic bombs . The pumpkin bombs were a means of providing realistic training for the 509th Composite Group ' s Boeing B - 29 Superfortress crews assigned to drop the atomic bomb after their deployment to the Pacific . The pumpkin bomb was a close but non - nuclear replication of the Fat Man plutonium bomb with the same ballistic and handling characteristics . Specifications for the bomb required that it be carried in the forward bomb bay of a Silverplate B - 29 bomber and be fuze d to be effective against actual targets . The name " pumpkin bomb " was given to the test bombs by Parsons and Dr . Charles C . Lauritsen of the California Institute of Technology , who managed the development team . The name was used in official meetings and documents , and probably referred to its large ellipsoid al shape . Although anecdotal sources attribute the naming of the bombs to painting them a pumpkin color , the bombs were painted olive drab or khaki , and photographs indicate that the units delivered to Tinian came painted in the same zinc chromate primer color worn by Fat Man . 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 the proximity fuze program , expected that it would involve considerable effort . The test program was initiated on 13 August 1943 at the Naval Proving Ground in Dahlgren , Virginia , where a scale model of the Fat Man plutonium bomb was developed . On 3 March 1944 , testing moved to Muroc Army Air Field , California . The initial tests demonstrated that the Fat Man assembly was unstable in flight , and that its fuzes did not work properly . Production . The pumpkin bomb shells were manufactured by two Los Angeles , California , firms , Consolidated Steel Corporation and Western Pipe and Steel Company , while the tail assembly was produced by Centerline Company of Detroit , Michigan . After initial development , management of the program was turned over to the U . S . Navy Bureau of Ordnance in May 1945 . A total of 486 live and inert bombs were eventually delivered , at a cost of between $ 1 , 000 and $ 2 , 000 apiece . Pumpkin bombs were produced in both inert and high explosive variants , with the inert versions filled with a cement - plaster - sand mixture combined with water to the density of the Composition B used in the high explosive versions . The filler of both variants had the same weight and weight distribution as the inner sphere used in the plutonium bomb . All of the inert versions were from the manufacturers directly to Wendover 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 ' s 393d Bombardment Squadron as training exercises . 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 a slurry , solidified in a drying facility for 36 hours , sealed , and shipped by railroad to the Port Chicago Naval Magazine , California , for shipment by sea to Tinian . Description . The pumpkin bombs were externally similar to the Fat Man bomb in size and shape , and both had the same square tail assembly and single - point attachment lug . The pumpkin bomb had three contact fuse s arranged in an equilateral triangle around the nose of the bomb while the atomic bomb had four fuse housings . The atomic bomb had its sections bolted together but most if not all of the pumpkin bombs were welded with a hole used for filling the shell . The Fat Man also had four external mounting points for radar antennae which the pumpkin bombs did not have . The pumpkin bombs were in length and in maximum diameter . They weighed , consisting of for the shell , for the tail assembly , and of Composition B filler . The shells were made of steel plate and the tail assemblies from aluminum plate . Combat missions . 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 . Mission parameters 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 and the aircraft then went into the sharp turn required on a nuclear mission . After the war the Strategic 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 . "