The Sherman DD, Duplex-drive or as many Allied soldiers called them the "Donald duck", was an amphibious tank design by the British in 1943 and 1944 for Operation Overlord. It was one of the tanks developed by Percy Hobart and his team. this design and others became known as Hobart's Funnies.
The development of this tank started in 1941 when a Tetrarch light tank had a Canvas screen fitted to the outside of the tank. This screen was made from waterproof Canvas and could be raised and lowers from inside the tank by the crew using a air pump and an inflatable rubber frame.The addition of the screen acting as a hull, increased the tanks freeboard, the distance between the water level and the top of the hull, allowing it to float. Around 460 Vickers Valentine were also converted to DD tanks before the decision was made to use the Sherman instead. This was partly due to the US armies unwillingness to use British due to training issues, and partly due to the Sherman being able to point its turret forward when the screen was up.This meant the tank was ready to fire as soon as it landed.
The alterations to the tank didn't just end the addition of a waterproof screen. Two duel propellers were also added to the back of the tank giving it its name the duplex drive. Tests were conducted at Bret reservoir and later in Portsmouth harbor. These tests took part very calm conditions a factor that would prove a serious problem on D-Day.
The DD Sherman first when into combat on the 6 June 1944 with varying levels of success. On sword beach DD from A and B squadrons, 13th/18th royal Hussars were launched 2.5 miles from shore and worked as planned reaching shore and assisting the infantry. Five tanks were not launched after the lead tank on the LCT, Landing Craft Tank, tore its screen. Another tank was lost after reportedly being rammed by a LCT.
On Gold beach things didn't go as swimmingly. The tanks were launched late and in rougher weather. Despite being launched just 640m from shore the Sherwood rangers Yeomanry lost 8 tanks before reaching the beach and even when they did Sherman crab, mine flail, tanks had already destroy the artillery and machine guns.
On Juno beach only tanks of the 1st Hussars attached to the 7th Canadian brigade reached shore. The launching distance varied between 3658m and 700m. 21 of 29 tanks reached the beach. 8th Canadian brigade on the eastern end of the beach landed without tank support due to the rough seas.
Utah beach saw 27 of the 28 launched tank of the 70th tank battalion reach shore. 4 tanks were lost when their LCT received a direct hit from artillery. The remaining tanks were launched 914m from shore however due to confusion landed 1829m from their intended target and saw little action.
Omaha Beach is, unfortunately, what most people remember the Sherman DD for. The tanks were launched 2 miles from the beach into bad weather and as a result only 2 of the 112 tanks assigned to this sector landed. As a result Omaha was the final and hardest beach captured on the 6th of June.
Sherman DD tanks were also used in operation Dragoon in the south of France on the 15th June 1944. 36 tanks were used in all and most were able to land. The Sherman DD did not see much combat for the rest of the war apart from small actions in Italy and at the crossing of the Rhine. There are few remaining DD tanks left although one can be seen at the Bovington tank museum in Dorset England.