Pumpkin bombs: High Explosive non-nuclear version of Fat Man
The concept for the pumpkin bomb originated with Navy Captain William S. Parsons of the Ordnance Division at Los Alamos and USAAF Colonel Paul W. Tibbets, commander of the 509th CG, on December 13, 1944, as a means of providing continued realistic training for the B-29 crews assigned to drop the atomic bomb after their deployment to the Western Pacific. The bomb would be a close but non-nuclear replication of the Fat Man plutonium bomb with the same ballistic and handling characteristics. Mission parameters would be similar to those of the actual atomic bomb missions, and all targets would be located in the vicinity of the cities designated for atomic attack.
The development of the bomb was managed by the California Institute of Technology under the direction of Dr. Charles C. Lauritsen. Specifications for the bomb required that it be carried in the forward bomb bay of a Silverplate B-29 and be fuzed to be effective against actual targets. The 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.
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 shipped 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 shape.
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, sealed, and shipped by railroad to the Port Chicago Naval Magazine, California for shipment by sea to Tinian. A total of 486 live and inert bombs were eventually assembled. These bombs were filled with 6000 pounds of Composition B High Explosive, a very formidable weapon. Description:
The pumpkin bombs were externally similar to the Fat Man bomb in size and shape, and both had the same 52-inch square tail assembly and single-point attachment lug. The pumpkin bomb had three contact fuses 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 four-inch hole used for filling the shell. The Fat Man also had four external mounting points for radar antennas which the pumpkin bombs did not have.
The pumpkin bombs were twelve feet eight inches in length and five feet in maximum diameter. The most commonly-given weight for the bombs is 5.26 tons, consisting of 3,800 pounds for the shell, 425 pounds for the tail assembly, and 6,300 pounds of filler. The shells were made of .375-inch steel plate and the tail assemblies from .200-inch aluminum plate. Although anecdotal sources attribute the naming of the bombs to painting them a pumpkin color, photographs indicate that the units delivered to Tinian came painted in the same Zinc Chromate primer color worn by Fat Man. 509th CG Combat use from Tinian:
Combat missions were flown by the 509th Composite Group between: July 20, 23, 26 and 29, and August 8 and 14, 1945, using the bombs against individual targets in Japanese cities, to practice dropping the Fat Man nuclear shape from the B-29 Superfortress. A total of 49 bombs were dropped on 14 targets, one was jettisoned into the ocean, and two were aboard aircraft that aborted their missions. More than 400 people were estimated killed and 1,200 others injured, in addition to the live ordnance dropped on Japan, several hundred inert bombs were used by combat crews of the 509th's 393rd Bomb Squadron to test the ballistics of the bomb shape in conjunction with Project Alberta, and to train bombardiers in mission procedures before movement of the group overseas.
Please note the photos attached: The easiest way to delineate between a Pumpkin and a Fat Man are the nose fuses: Pumpkin had three and Fat Man had four plugged fuse mounts, very easy to differentiate when you know what to look for. The attached photos clearly show the three nose fuse design of the Pumpkin. Photo  Pumpkin bomb on trailer at Wendover Air Field Photo,  Pumpkin bombs on barge Tinian harbor July 1945. Pumpkin being off loaded at Tinian harbor.
The attached video courtesy of the Smithsonian Air & Space magazine By Carl Posey; This video is of a Fat Man bomb test Drop from Kirtland AAFB from the bomb bay viewing point. There is an error in this video as the commentator is describing to yellow/orange color of the pumpkin bomb. At this section of the video is inserted a video clip of F-31 the combat unit used on Nagasaki being prepped outside the bomb assembly building on Tinian, you can clearly see the four plugged fuse mounts on F-31. Also at the point of drop from the B-29 it is unclear if this is a Fat Man or Pumpkin as one cannot see the nose of the bomb at release.
Both Fat Man (FM) and Pumpkins were used in drop testing flights originating from (post war - Kirtland Field, NM), Wendover Field, UT, Inyokern (Harvey Field, CA)/ Sandy Beach - (Salton Sea, CA), China Lake NOTS (Armitage Field, CA) as well as early FM tests a Muroc. The walking the prop segment of this video may strike a chord
with some veterans...
As this video is not You Tube imbedded here is the link: http://www.airspacemag.co.../Pumpkin-Practice.html
Well, I hope you enjoy the film, its short so popcorn will not be required.
Edited by 25Kingman49: added clarity to drop test locations.
post edited by 25Kingman49 -