The story of the Duplex Drive, or DD, tanks is well-covered elsewhere. David Fletcher's Vanguard of Victory from HMSO provides a very good picture of the British origins of this project. There is a popular misconception that all DD tanks were all British manufactured conversions on the Sherman, but in fact, there was a distinct US version as well. US officers were shown early British trials with the Valentine DD tanks and discussed the Sherman DD programme with their British counterparts during planning for Operation Neptune, the code word for cross-channel operations within Operation Overlord, the D-Day landings in Normandy. In November 1943, the US Army set a requirement for 350 M4A1 DD tanks, enough for three battalions and an ample surplus for training and spares. Drawings of the British design were sent to the US in early 1944, and the conversion kits were manufactured by Firestone, the well-known tyre manufacturer. Conversion of the tanks was undertaken at the Lima Tank Depot in Ohio starting in February 1944 and a total of two pilots and 348 serial production tanks was completed. Curiously enough, the M4A1 cast-hull Sherman was selected for the conversion on the grounds that the 'streamlined hull' would perform better in water, ignoring of course the fact that the exposed bits were identical to other Shermans!
Download from (hotfile.com) or (filesonic.com)
