Silverplate
Silverplate was the code reference for the United States Army Air Forces' participation in the Manhattan Project during World War II.
Originally the name for the aircraft modification project which enabled a B-29 Superfortress bomber to drop an atomic weapon, "Silverplate" eventually came to identify the training and operational aspects of the program as well.
Modifications began on a prototype Silverplate B-29 known as the "Pullman" in November 1943, and it was used for bomb flight testing at Muroc Army Air Field in California commencing in March 1944.
[1] Prior to the decision to use the B-29, serious consideration was given to using the British Avro Lancaster with its cavernous 33-foot (10 m) bomb bay to deliver the weapon.
It would have required much less modification but would have necessitated additional training for the United States Army Air Forces (USAAF) crews.
[2] The superior range and high-altitude performance of the B-29 made it much a better choice, and after the B-29 began to be modified in November 1943 for carrying the atomic bomb, the suggestion for using the Lancaster never came up again.
Arnold and the head of the Ordnance Division at Los Alamos, Captain William S. Parsons, arranged for tests to be carried out at the Naval Proving Ground in Dahlgren, Virginia, in August 1943.
[7] Originally the name for the aircraft modification project for the B-29 to enable it to drop a nuclear weapon, Silverplate eventually came to identify the training and operational aspects of the program as well.
[9] The USAAF sent instructions to its Army Air Forces Materiel Command at Wright Field, Ohio, on 30 November 1943 for a highly classified B-29 modification project.
[1] The Manhattan Project would deliver full-sized mockups of the weapons shapes to Wright Field by mid-December, where Army Air Forces Materiel Command would modify an aircraft and deliver it for use in bomb flight testing at Muroc Army Air Field in California.
[14] High speed photographs revealed that the tail fins folded under pressure, resulting in an erratic descent.
[15] The Thin Man gun-type design was at that time based on the fissibility of the very pure plutonium-239 isotope so far only produced in microgram quantities by the cyclotron at University of California, Berkeley.
When the Hanford Site production reactors came on-line in early 1944, the mix of plutonium-239 and plutonium-240 obtained was found to have a high rate of spontaneous fission.
To avoid pre-detonation, the muzzle velocity of the gun-type design needed to be greatly raised, making it impractically long.
The muzzle velocity required was much lower,[17] reducing the barrel length of the resulting bomb, code-named Little Boy, to less than 10 feet (3.0 m).
It carried out further drop testing with the 216th Army Air Forces Base Unit until it was damaged in a landing accident in December.
[19] On 22 August 1944, to meet the requirements of the USAAF group about to be formed to train in the atomic mission, a production phase of Silverplate B-29s was ordered from the Glenn L. Martin Company's modification center at Offutt Field, south of Omaha, Nebraska, under the designation Project 98146-S.[20] The first three of these second increment Silverplate B-29s were delivered to the USAAF in mid-October and flown to Wendover.
A new crew position, called the "weaponeer station", was created in the cockpit with a panel to monitor the release and detonation of the bomb during the actual combat drops.
[21] Fourteen production aircraft were assigned to the 393d Bombardment Squadron for training, and three to the 216th Army Air Force Base Unit for bomb drop testing.
Four of the planes assigned to the 393d Bombardment Squadron (now part of the 509th Composite Group) were transferred to the 216th to meet an increase in its testing tempo.
[24] The fuel-injected Wright R-3350-41 engines in the later model bombers delivered in July and August 1945 were greatly improved and far more reliable.
[26] Each Pumpkin bomb mission was conducted by a formation of three aircraft in the hope of convincing the Japanese military that small groups of B-29s did not justify a strong response.
The pair of historic weapons delivery aircraft, named Enola Gay and Bockscar, are currently displayed in museums.
One other Silverplate B-29, on temporary assignment in the United Kingdom, was converted into a weather reconnaissance aircraft (WB-29) and transferred to the 9th Bombardment Wing at Travis Air Force Base in California.
