The British made a significant advancement in their capability to carry out amphibious assaults with the development of the Duplex Drive system. This system involved the use of a Sherman DD tank equipped with a collapsible flotation screen which could be locked in place by metal struts. A deck was welded to the Sherman’s hull and the screen was permanently attached to it. Inflation of 36 rubber air pillars, powered by two compressed-air bottles located on the rear decking, caused the screen to erect. The other component of the Duplex Drive was a double propeller system which was driven by the bevel drive of the tank and provided a water speed of 4.6 mph (7.4 km/h).