In what might have been the most audacious tactic of the Second World War, the Western Allies committed nearly half the tanks supporting the D-Day landing to the Duplex Drive (DD) or "Swimming Shermans".
The engines that drive the tracks also powered twin propellers when the tank was afloat. In essence this amounted to 34 tons of steel and five men in a canvas bag with propellers.
The main lesson from the failed Dieppe Raid in 1942 was that infantry assaulting a defended beach would suffer unacceptable casualties without supporting armour. The intent was to have the tanks come ashore just ahead of the infantry to clear out machine gun nests and other strong points.
Duplex Drive Tanks
It was thought that ships bringing tanks directly to shore would be vulnerable to sinking or damage by artillery and be unable to unload. Two squadrons from each of the 1st Canadian Hussars from London, Ontario and the Fort Garry Horse of Winnipeg supported the Canadian infantry that assaulted Juno Beach.
Unfortunately for the tank men, the seas on D-Day were very rough, almost twice as high as designed for and many tanks went to the bottom on launching or enroute when the canvas screens collapsed from wave pressure taking most of the crews with them. In many cases it was decided to bring the tanks ashore by boat, however many arrived after the infantry had already landed.
The greatest losses were at Omaha Beach where the duplex-drive ‘swimmers’ were launched almost a mile or nearly two kilometres from shore in the roughest of seas. Only 2 of the 31 tanks reached shore. The 1st Canadian Hussars lost 8 tanks to the sea, representing more than 10% of Canada’s fatalities on D-Day. Their names may be seen on the columns of those with no known grave at the cemetery at Bayeux.
The idea of making tanks amphibian was the brain child of Percy Hobart. Floatation on the Swimming Shermans was achieved by a heavy canvas screen attached to a flange that circled the tank body above the tracks. Everything below the tracks was sealed and made waterproof. The accordion folded canvas screen, was raised by filling vertical tubes with high pressure air to become the sides of the "boat".
The tank hull contributed little to the buoyancy. There was about three feet of freeboard when fully loaded with a 35 ton tank, ammunition and crew. After raising the screens, the sides were reinforce with metal struts. The bow and stern were higher that the sides to improve seaworthiness. Propulsion was provided by two propellers powered by the track drive system. Speed was about two miles per hour.
As soon as the tracks touched the bottom the front half of the screen was lowered and the gun brought into action. Since the stern was in deeper water and subject to following waves, the rear screen remained up to protect the air intake.
"Swimming Shermans" were used at all five invasion beaches. The plans were to launch from 5000 to 7000 yards from shore with time to arrive ahead of the infantry. However sea conditions varied from beach to beach, many tanks had dry landings and others were brought much closer for launching. About 300 DD tanks were involved with the Normandy invasion. Of the 170 that were launched 59 were lost to the sea and the remainder landed dry or had a short wade.
At Omaha Beach, after the first five tanks launched went straight to the bottom, it was decided to land the remaining 27 tanks on shore.Without doubt the presence of the DD Tanks on the Normandy beaches was one of the factors that kept Canadian casualties much lower than expected. ‘Swimming Shermans’ were used later at the Scheldt Estuary, the Po River in Italy, the Rhine River crossing and the landing in Southern France. All of these were on calm water.
In retrospect, going into action in a "Swimming Sherman" was serving ones country at extreme risk. Considering the added hazard of drowning due to the stormy seas, to quote Max Hastings, on D-Day, "a special kind of sacrificial heroism was demanded of the Duplex Drive crews."
D-Day, June 6th, 1944, is remembered in many different ways by those still living. Memories of the flyers or sailors who participated on that day are theirs and they are not the same as the men of the airborne regiments who jumped or landed in gliders on that day. Even each individual of the Canadian Third Division or Second Armoured Brigade has their own set of memories. But the 400 men who manned the 80 "Swimming Sherman" Tanks (better known as Duplex Drive or DD Shermans) have memories that are unique to that innovative and audacious piece of military equipment.
Almost everyone who left England with the intent of landing on the Normandy beaches remember sighting the French shore when daylight was just breaking, when the naval barrage thundered behind them; the shells rumbling like freight trains. Hundreds of bombers and fighters roared overhead to bomb and strafe.
It all created a terrific noise. Everybody remembered the noise. Then as daylight spread, the further one looked left, right and near were ships of every description. They were part of the greatest Naval armada ever assembled. These are common memories to every participant who witnessed that day.
For the 400 Canadians and similar numbers of British and Americans in DD tanks it was a bit different. They had trained in calm lakes and placid inland waters. The DD tanks crossed the channel five to an LCT (Landing Craft Tank) a relatively small ship that was pounded unmercifully by the rough seas.
Most of the men were so sea sick that those who reached the shore were sick for days afterward. But what are the memories of those that are still alive – they weren't all sea sick! On the other hand, they had their minds fixed on that rough sea for quite some time. They wondered, would their tank be able to make it to shore under those perilous conditions?
Then word came to the Brits, the Americans and to the Canadians, who all used DD tanks, "Inflate your screens!", the ramps went down and the crew commanders yelled "Driver prepare to advance." So this was it! Many didn't live to remember it. The Americans lost a great many tanks. The First Hussars lost most of their tanks in one squadron and several from the other. "C" Squadron of The Fort Garry Horse lost 3 by sinking, "B" Squadron landed dry, "C" Squadron lost 13 men on D-Day, 11 drowned and 2 by sniper fire.
For all those who made it to shore with their tanks it must have seemed the longest trip ever taken. They moved at 5 to 6 miles per hour, sometimes even slower, depending on the waves. All the way from launch to landing, they must have been thinking, "of all the men in this army, how did I get stuck in this 35-ton monster held up in the ocean by a canvas screen".
But then they might have remembered the men who went to war in gliders and wondered when they landed, would they still be alive? Of the hundred men in "C" Squadron who went to war in DD Tanks, 25 were killed during the first few hours of D-Day. The ones who survived the battle and then the war, the memory of that momentous and historical event, remained forever etched into their collective memory.