October 2, 2014

DD Sherman

DD Sherman
A Sherman DD tank, with its flotation screen removed, passing through Douet on 25 June 1944. 
DD stands for Duplex Drive or Donald Duck!


The Normandy amphibious assault demanded a tank that could be launched into the sea and then swim until it had reached firm ground where it would drive ashore. Nicholas Straussler (1891 – 1966) working at Vickers-Armstrong had developed a method that would allow a tank to float.

By erecting a collapsible canvas screen around the tank’s hull the tank’s displacement was increased sufficiently. Therefore, the tank’s hull, although submerged it floated. To be able to steer the tank was fitted with propellers at its rear end. The tests were performed successfully with a Valentine tank but it was decided that the design would be applied to Shermans, the most numerous tank in the invading armies.  

On the Sherman DD the canvas was erected by compressed air and was supported by a metal frame. Once ashore a small explosive charge collapsed the flotation screen and the propellers were disengaged.

DD Sherman
2. A DD Sherman with its flotation screen lowered.

DD Shermans crossing the Rhine
3. DD Shermans crossing the Rhine on 24 March 1945.

DD Shermans crossing the Rhine
4. DD Shermans during the crossing of the Rhine.

DD Sherman


Bibliography
Forty, George. World War Two Tanks. Osprey, 1995.
Hogg, Ian V. Allied Armour of World War Two. Ramsbury: Crowood, 2000.


Photos attribution
No 5 Army Film & Photographic Unit, via Wikimedia Commons