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. The original directive for the project had as its subject line "Silver Plated Project" but continued usage of the term shortened it to "Silverplate".
Testing began with scale models at the Naval Proving Ground in Dahlgren, Virginia, in August 1943. 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. The testing resulted in further modifications to both the bombs and the aircraft.
Seventeen production Silverplate aircraft were ordered in August 1944 to allow the 509th Composite Group to train with the type of aircraft they would have to fly in combat, and for the 216th Army Air Forces Base Unit to test bomb configurations. These were followed by 28 more aircraft that were ordered in February 1945 for operational use by the 509th Composite Group. This batch included the aircraft which were used in the atomic bombings of Hiroshima and Nagasaki in August 1945. Including the Pullman B-29, 46 Silverplate B-29s were produced during and after World War II. An additional 19 Silverplate B-29s were ordered in July 1945, which were delivered between the end of the war and the end of 1947. Thus, 65 Silverplate B-29s were made.
The use of the Silverplate codename was discontinued after the war, but modifications continued under a new codename, Saddletree. Another 80 aircraft were modified under this program. The last group of B-29s was modified in 1953, but never saw further service.
Origin
The Silverplate project was initiated in June 1943 when Dr. Norman F. Ramsey from the Los Alamos Laboratory's E-7 Group identified the Boeing B-29 Superfortress as the only airplane in the United States inventory capable of carrying either type of the proposed weapons shapes: the tubular shape of the Thin Man, or the oval shape of the Fat Man.
Prior to the decision to use the B-29, serious consideration was given to using the British Avro Lancaster with its cavernous bomb bay to deliver the weapon. It would have required much less modification, but would have required additional crew training for the USAAF crews. Major General Leslie R. Groves Jr., the director of the Manhattan Project, and General Henry H. Arnold, the Chief of United States Army Air Forces (USAAF), wished to use an American plane, if this was at all possible.
The first B-29 was delivered to the USAAF on 1 July 1943, and Groves met with Arnold later that month. Groves briefed Arnold on the Manhattan Project, and asked for his help in testing the ballistics of the Project's proposed bomb shapes. 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. No aircraft was available that could carry the long Thin Man, so a scale model was used. The results were disappointing – the bomb fell in a flat spin – but the need for a thorough test program was demonstrated.
Groves met with Arnold again in September 1943. He informed Arnold that there was now a second bomb shape under consideration, the Fat Man, and formally requested that further tests be carried out, that not more than three B-29s be modified to carry the weapons, and that the USAAF form and train a special unit to deliver the bombs. Arnold delegated responsibility for this to Major General Oliver P. Echols. In turn, Echols designated Colonel Roscoe C. Wilson as the Project Officer.
Codename
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. The airplane modification project fell under the purview of the Manhattan Project's Project Alberta after March 1945. The original codename for the project was "Silver Plated" but continued usage of the term shortened it to the one word "Silverplate". For security reasons, the codename "Silverplate" was not officially registered. Confusion then resulted when the War Department allocated "Silverplate" to another project. Arnold's office had to order the other agency to discontinue its use of the codename.