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Blog Topic: B-29s and the Silverplate Bombers

April 19, 2015

Silverplate bomber

Silverplate bomber The Great Artist. This aircraft participated in the atomic bombing missions at Hiroshima and Nagasaki. USAF photo.

The B-29 was one of the most advanced bombers of World War II. It was the first production bomber to have pressurized cabins for the crew. A big airplane with twin bomb bays, it had a regulating device to ensure that bombs were dropped by even weight from both bomb bays. This bomber had a remote control gun system where an individual gunner was able to control and fire more than one turret at a time with a lightweight aiming device.

Aerodynamically designed with a curved front Plexiglas enclosure, the B-29's pilot and co-pilot looked out of curved glass, instead of flat plate glass. Unintentionally, this resulted in a certain amount of parallax, where objects appeared to be offset a little from where they really were, when viewed through the curved Plexiglas. Charles Sweeney, in his book the War's End, comments about General LeMay, who at one point evidently misjudged the position of the aircraft to the runway because of the parallax, and was in danger of putting a landing wheel into the mud, off of the paved runway.1 Although the parallax required compensating adjustments be made by the pilot it did contribute aerodynamically to the design of the B-29, which was the first U.S. bomber to use this feature.

Within the whole framework of specialization, and new cutting edge features on the B-29, there were a series of B-29s that were further modified to drop the atomic bombs at Hiroshima and Nagasaki. These became known as the Silverplate bombers2. The forward bomb bay was modified to take one single 10,000 pound bomb, which was unique for the U.S. Army Air Force at that time. The rear bomb bay was modified to carry an extra 600 gallon fuel tank. A pit was built which included a hydraulic mechanism to facilitate bomb loading.

As testing with the atom bomb progressed, it was found that the amount of extra crew members and special equipment needed, would cause the Silverplate B-29s to become overloaded. On order of Colonel Tibbits, commander of the 509th Composite Group, the four turrets, two gunners, and the original bomb regulating device, were deleted from these bombers to save weight. Turrets were plated over, flush with the aircraft, to remove aerodynamic penalty, and the gunners side observation windows were reduced to approximately 10% of the original size, to partially block the brightness from an atomic bomb explosion. Only the tail gunner and turret was kept the same. The first fifteen Silverplate bombers had these modifications made after leaving the factor; the next fifteen were modified before leaving the factory.

~ Jon

1 Charles Sweeney, War's End. New York: Avon Books, 1997. p.79.
This incident took place while briefing General LeMay, who was taking command of all the B-29s in the Pacific. They actually did some test flights with the general flying the B-29. Sweeney was all set to grab the controls, but at the last instant, General LeMay realized his error, gunned the engines, pulled up the landing gear, and went around for another pass.
2 Silverplate was the code name for the U.S. Army Air Force project which used the atomic bombs produced by the Manhattan Project.


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