M4A1 Sherman DD
The Sherman DD tank was devised as an amphibious tank that didn’t need to be brought to shore in a landing craft, reducing the risk of vital landing ships becoming easy targets during the initial phase of the landing. The swimming tanks could arrive at the beachhead before or with the first infantry wave offering essential fire support against the defenders positions.
The Sherman DD wasn’t the first tank to be fitted with the unique Duplex Drive (DD) system. The Nicholas Straussler idea was initially tried on a number of British tanks during its development from 1941. In fact many of the US, Canadian and British Sherman DD crews on D-Day had trained initially with Valentine DD tanks. By 1944 it was decided that the Sherman was a more suitable tank for conversion to the DD system.
The Duplex Drive system worked by the combination of normal tracks and two propellers to increase propulsion while swimming. A rudder was fitted for steering. For buoyancy a folding screen of water-proofed canvas was fitted around the hull mounted on horizontal metal hoops, further buoyancy, support and rigidity was added by 36 rubber tubes that could be inflated by the crew with a compressed air system. The lower hull was sealed to keep the tank from flooding. Once ashore the crew could quickly remove the flotation system when the first chance arrived (when they weren’t being shot at).
The first full-scale use of the Sherman DD in action occurred during D-Day. The Sherman DD tanks were designed to be released from the landing ships two miles off shore and swim to the landing beaches to arrive with or before the first waves of infantry. Due to the mixed weather of 6 June 1944 the Sherman DD tanks arrived at the various beaches with mixed results. On Sword beach they arrived much as planned due to the good sea conditions. They were launched 2.5 miles out and 32 of the 34 launched arrived at the beach to give cover to the assaulting troops.
On Gold the sea was deemed too rough for the DD tanks and they were landed from the landing ships directly on the beach so didn’t arrive until after the other fighting vehicles. They took heavy anti-tank fire but were ultimately successful.
The Canadian Sherman DD tanks on Juno were only able to launch one of the two battalion so equipped. They were launched a mere 800 yards from the shore, despite this only 21 of the 29 made it ashore.
They only arrived after the first wave of infantry had landed and they weren’t able to prevent the first wave taking heavy casualties. However they played a vital role in reducing the German defences and allowing the Canadian to advance inland. On the US beaches the DD tanks achieved mixed results. On Utah they struck an early setback when one landing ship struck a mine and sank taking four tanks with it. The remaining 28 launched and made it to shore, but made slow progress and were overtaken by the infantry landing craft so didn’t arrive until 15 minutes after the first wave hit the beach. However they were able to provide vital cover and support fire and went some way to contributing to the light US casualties on Utah.
On Omaha the Sherman DD tanks would play virtually no role at all due to a combination of bad luck and mismanagement. A total of 64 DD tanks were assigned to Omaha, split between the 741st and 743rd Tank Battalions. Only the 741st battalion launched it’s Sherman DD tanks into the sea. Unfortunately the sea was quite rough and the decision to launch was made prematurely (at about 3 miles out). The large, up to 6 foot, swells overwhelmed all but two of the tanks during the journey to the beach. Their cause was not help by navigation issues that forced many tanks to turn to with their flanks to the waves to try and maintain their course to the landing zone. The large waves simply hit the tanks side-on and swamped them. The Sherman DD tank was also used during Operation Dragoon when the south of France was invaded by the Allies on 15 August 1944. Small numbers were also used during Operation Plunder, the crossing of the Rhine on 23 March 1945.