History
Before the Allied landings on D-Day in the summer of 1944, it became clear that armored support during the initial assault would be vital to the success of the Normandy invasion. Lessons learned from the disastrous Dieppe Raid in 1942 showed that tanks were quite vulnerable during disembarkation. Landing craft that launched tanks directly onto the beaches left them exposed to enemy fire. To solve this flaw, the Allies sought a solution that could be used to launch tanks at sea and swim under their own power to the shore, reducing exposure and giving immediate support to infantry forces.
This concept led to the development of the Duplex Drive (DD) tank, a project spearheaded by Nicholas Straussler, a Hungarian-British engineer. In May 1942, Straussler’s first successful prototype, based on the Valentine infantry tank, demonstrated the feasibility of amphibious armor. These early DD tanks used a canvas flotation screen that surrounded the tank like a skirt, allowing it to float. Propellers mounted under the rear deck propelled the tank through water.
By April 1943, however, the Valentine was deemed obsolete for frontline combat. Major General Percy Hobart, architect of “Hobart’s Funnies,” known for the specialized armored vehicles, recommended applying the DD equipment to the more capable and widely used M4 Sherman tank.
Because the Sherman was significantly larger and heavier than the Valentine, the flotation device had to be redesigned. The modified system consisted of a collapsible rubberized canvas screen mounted on a mild steel platform welded around the hull. The screen was raised by inflating 36 rubber pillars with compressed air and held in place by 13 locking struts to prevent sudden collapse. To improve stability and resist water pressure, three tubular steel frames encircled the canvas at different levels, with increasing screen thickness below each frame. The screen was bolted and sealed tightly to prevent leakage.
When the tank reached land, the flotation screen could be rapidly collapsed by releasing the hydraulic locks and deflating the pillars. Elastic bands folded the canvas, clearing the turret and gun for immediate combat. Air for the flotation system was supplied by bottles mounted on the hull front.
The Sherman DD could swim in water of any depth and was powered by two 26-inch propellers connected to the drivetrain, rotating in opposite directions. Steering was managed either manually or hydraulically, and could be controlled by the driver or commander. Once ashore, the propellers were disengaged and swung upward for ground clearance.
Deliveries of the Valentine DDs began in July 1943, and training programs soon followed. Five British and two Canadian armored regiments, along with three US tank battalions, participated. On January 27, 1944, a demonstration impressed General Dwight D. Eisenhower, who approved the deployment of Sherman DD tanks to support infantry during the Normandy invasion.
The US received its first batch of 100 Sherman DDs soon after. These were primarily large-hatch M4A1 (75) Shermans, equipped with features like the M34A1 gun shield, cast appliqué armor, and heavy-duty bogies with improved return rollers. While the US Army used M4 and M4A1 variants, the British Army converted M4A2 and M4A4 Shermans to DD configuration. The British Army was also supplied with American M4A1 DDs.
Among the American units trained on the DD tanks were the 70th, 741st, and 743rd Tank Battalions. On D-Day, the 70th landed at Utah Beach, while the 741st and 743rd were assigned to Omaha Beach.
The DD tanks were launched up to two miles (about 3 km) from shore. At Utah Beach, the 70th Battalion’s DD tanks performed well, with only a few losses in submerged sandbars.
At Omaha Beach, conditions were far worse. Rough seas and high swells overwhelmed the DD tanks of the 741st Battalion. Of 32 tanks launched, only 2 reached shore, and the rest were swamped or sank. Three tanks remained stuck on their landing craft. The 743rd, recognizing the dangerous conditions, landed their DDs directly instead of launching them offshore, though they lost 8 tanks to German fire. Those remaining Sherman DD tanks supported the infantry on Omaha Beach.
Despite these setbacks, Sherman DD tanks proved their worth, helping secure the beachhead and later fighting further inland in Normandy.
Sherman DDs were also used during Operation Dragoon, the Allied landing in southern France on August 15, 1944. Units like the 191st, 753rd, and 756th Tank Battalions landed with minimal losses.
Following Normandy and southern France, the DD tanks were reassigned to river crossing operations across northwestern Europe. One of their most notable successes came during the Rhine crossing in March 1945, where the American Sherman DD tanks crossed the river without major issue. The final recorded use of Sherman DDs was during the crossing of the River Elbe at Artlenburg by the British Staffordshire Yeomanry on April 29, 1945.
