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DD tank
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DD tanks (for Duplex Drive, but nicknamed Donald Duck tanks) were amphibious swimming tanks developed during the Second World War. The phrase is mostly used for the M4 Sherman medium tanks used by the Allies in the opening phases of the D-Day landings in 1944.
The swimming tracked Landing Vehicle Tracked (LVT) had already been used in the 1942-43 Solomons campaign in the Pacific, swimming 2 1/2 ton trucks in the 1943 invasion of Sicily, swimming Ford jeeps appeared in 1944, and the Soviets had developed swimming tankettes in the 1930s --but swimming medium tanks presented their own design problems.
The swimming tank idea arose when it was realised that the first waves of infantry that reached an invasion beach would be acutely vulnerable without the support of tanks.
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DD tanks (for Duplex Drive, but nicknamed Donald Duck tanks) were amphibious swimming tanks developed during the Second World War. The phrase is mostly used for the M4 Sherman medium tanks used by the Allies in the opening phases of the D-Day landings in 1944.
The swimming tracked Landing Vehicle Tracked (LVT) had already been used in the 1942-43 Solomons campaign in the Pacific, swimming 2 1/2 ton trucks in the 1943 invasion of Sicily, swimming Ford jeeps appeared in 1944, and the Soviets had developed swimming tankettes in the 1930s --but swimming medium tanks presented their own design problems.
The swimming tank idea arose when it was realised that the first waves of infantry that reached an invasion beach would be acutely vulnerable without the support of tanks. But if landing craft were used to carry those tanks, they themselves would be vulnerable to German heavy guns. The loss of too many landing craft would slow the movement of reinforcements from ships offshore and the invasion beaches would be choked with disabled and sunken landing craft. By giving tanks the ability to float, they could be launched from landing craft several miles from the shore and make their own way onto the beach.
The DD tanks were one of the many specialised assault vehicles, collectively known as Hobart's Funnies, derived to support the beach landings. All were extensively used by the British and Canadians, but the DD tanks were the only ones adopted by the American forces. It has been speculated that if the DD tanks were better used, or if some of the other specialised vehicles had been used, that American losses on the beaches of Normandy, particularly Omaha beach, would have been far less.
Development
Amphibious tanks were devised during the First World War, a floating version of the British Mark IX tank was being tested in November 1918, just as the war ended. Development continued during the interwar period. Swimming tanks are generally of two kinds:
- some with natural buoyancy, these were generally either too small to be useful or so large as to be impractical.
- others were normal tanks with attached floatation devices, but these were too big to fit onto landing craft.
In 1941, the Hungarian-born Nicholas Straussler working in Britain solved the problems faced by other swimming tanks with the idea of a folding screen made of waterproofed canvas. This made tanks buoyant without adding much size, but was only useful in calm water.
The first tank to be experimentally fitted with a floatation screen was a Tetrarch tank and its first trial took place in June 1941 in Brent Reservoir (also known as Hendon Reservoir) in North London in front of General Alan Brooke. Curiously, this was also where trials of the floating version of the Mark IX tank took place, 23 years before. Satisfactory sea trials of the Tetrarch took place near Hayling Island, in Portsmouth Harbour, and the go-ahead was given to develop a production DD tank based on the Valentine tank.
The majority of the American, British and Canadian DD tank crews did their preliminary training on the Valentine DD which incurred several losses.
By 1944, it was clear that the Sherman tank was more suitable for use with screen than the Valentine, one reason being that it could move in water with its gun forward ready to fire as soon as land was reached. The Valentine was also an older and generally inferior design. Modifications to the Sherman included sealing of the lower hull, the addition of the propeller drive and the addition of Straussler's flotation screen around the hull, together with its inflation system.
The canvas floatation screen was attached to a metal frame welded to the tank's hull. The screen was supported by horizontal metal hoops and by 36 vertical rubber tubes. A system of compressed air bottles and pipes inflated the rubber tubes to give the curtain rigidity. The screen could be erected in 15 minutes and quickly collapsed once the tank reached the shore. In combat, the flotation system was considered expendable and it was assumed the tank crew would remove and discard it as soon as conditions allowed.
A pair of propellers at the rear provided propulsion. One problem presented by the Sherman was that the configuration of the transmission made it impossible to take a drive-shaft for the propellers directly from the gearbox. The solution to this was to have sprocket wheels at the rear of the tank so power was delivered to the propellers by the tank's tracks. DD Tanks could swim at up to 4 knots (7 km/h).
Both the commander and the driver could steer in the water. A hydraulic system under the control of the driver could swivel the propellers. The commander stood on a platform on the turret, where he could see over the skirt, and steered the tank with a large tiller.
Designs were even made to give the Cromwell and Churchill tank the DD treatment, but these were never finished. A floating, flame-thrower equipped version of the Universal Carrier was tested, as was a flamethrower-equipped DD Sherman. This towed an armoured fuel trailer, like those used by the Churchill Crocodile Flame tank; in the water, the trailer was supported by an inflatable floatation device.
After the war, the Centurion tank was tested with flotation screen and duplex drive. By the end of the 1950s, development of DD tanks had ceased partly because main battle tanks were becoming too heavy to be practically made to swim. Although experiments were made in the mid-1960's with a floating Centurion that used a similar system, but with rigid panels instead of a flexible screen..
Medium and light vehicles continued to be made amphibious by the use of flotation screens into the 1980's, but without the DD. Instead they used the movement of their standard running gear (e.g. tracks) for water propulsion also. These included the Swedish Stridsvagn 103 (S-Tank), the American M551 Sheridan light tank, the British FV432 Armoured personnel carrier, the Mark IV version of the Ferret armoured car and early versions of the American M2 Bradley Infantry Fighting Vehicle. Of these, only the FV432 and the Bradley remain in service and current versions lack flotation screens.
Combat
The main use of DD tanks occurred on D-Day. They were also used in Operation Dragoon, the Allied invasion of southern France, on 15 August, 1944. Limited numbers were also used during Operation Plunder, the British crossing of the Rhine on March 23, 1945.
D-Day
The DD Sherman was used to equip ten tank battalions of British, Canadian and American forces for the D-Day landings. They were carried in Tank landing craft (LCT)s. These could normally carry nine Sherman tanks, but could fit fewer of the bulkier DD's . British and Canadian LCTs carried five tanks, the Americans carried four DD's as their LCT's were shorter at about 120 ft.
The DD's would be launched around two miles offshore, they would swim to the beaches and overpower German defenses unprepared for attack tanks. In the event, the tank's record was a mixture of success and failure, although they are mainly remembered for their disastrous failure on Omaha Beach.
Sword Beach
On the British Sword Beach, at the eastern end of the invasion area, the DD tanks worked well, as the sea was reasonably calm. The DD tanks were launched two and a half miles (4 km) from shore. Five could not be launched as an LCT's leading tank tore its screen - they were later landed directly on shore - and one tank sank after being struck by an LCT.
Gold Beach
On Gold Beach, the sea was rougher. The tanks of the Sherwood Rangers Yeomanry were launched late, 700 yards (600 m) from the shore. Eight tanks were lost on the way in and by the time the remainder landed, Sherman Crab mine flail tanks had already destroyed the German artillery and machine-gun positions that would have been their objective. The sea conditions meant the tanks of the 4th/7th Royal Dragoon Guards were landed in the shallows. They then drove onto the beach with their screens up so they wouldn't get swamped in the breakers. German anti-tank guns caused heavy losses in some sectors of the beach but the assault was successful.
Juno Beach
On the Canadian Juno Beach, The Fort Garry Horse and the 1st Hussars were equipped with DD tanks, but only those of the 1st Hussars could be launched. They were assigned to the 7th Canadian Brigade, on the western end of the beach. Some of the tanks were launched at 4,000 yards (3,600 m) and some at 800 yards (700 m); twenty-one out of twenty-nine tanks reached the beach. The 8th Canadian Brigade, on the eastern end of the beach, was forced to land without DD tanks because of rougher seas. They suffered heavy initial casualties, but were still able to make good progress.
Utah Beach
On Utah Beach, the DD's were operated by the 70th Tank Battalion. Four of the DD tanks were lost when their LCT was lost to German artillery fire. The remaining tanks were launched 15 minutes late at a point 1,000 yards (900m) from the beach. Twenty-seven out of twenty eight reached the beach but confusion caused by the massive smoke screen meant they landed around 2,000 yards (1,800 m) from their aiming point and saw little German opposition.
Omaha Beach
At Omaha Beach almost all of the tanks launched offshore were lost, contributing to the high casualty rate and slow progress at that beach.
There were 112 tanks assigned to the first wave at Omaha Beach, with 56 tanks in each of the 741st and 743rd Tank Battalions. Each of these battalions had 32 DD Shermans and 24 other Shermans (including many Sherman bulldozers for clearing obstacles). Starting at about 0540, the 741st Tank Battalion put 29 DD Shermans into the sea, but 27 of these sank and only two made the long swim to the beach. Some of the crews of the sinking tanks managed to radio back and warn following units not to launch as far out. The remaining tanks of the 741st Tank Battalion and all tanks of the 743rd Tank Battalion (except for 4 tanks aboard one LCT that was hit by artillery fire just off the beach) were landed directly on the beach, starting at about 0640.
The DD Tanks were designed to withstand waves up to 1 foot (0.3 m) high; however, on that day the waves were up to 6 feet (2 m) high. These were much worse conditions than the tanks had been tested in and thus they were swamped with water. Also, the tanks of 741st Tank Battalion were released into the sea too far out, about 3 miles (5 km) offshore. Considering the inherent difficulty in steering a 35 ton modified tank, it is a tribute to the crews that they got as far as they did. The crews were equipped with emergency breathing apparatus capable of lasting 5 minutes, and the tanks were also equipped with inflatable rafts.. Some sources claim that these life-saving measures were ineffective, - contradicted by the testimony of survivors.. Most of the crews were rescued, mainly by the landing craft of the 16th RCT (Regimental Combat Team) although five crewmen are known to have died during the sinkings.
Until very recently it was believed that most of the DD Shermans of 741st Tank Battalion were sunk immediately, swamped by the seas that were much higher than the operators had practiced with. Some stayed afloat for a matter of minutes; according to the crews one tank swam for 15 minutes before sinking, another "We weren’t in the ocean 10 minutes when we had a problem" Tanks at the other four beaches suffered no such problems. New research suggests that the Omaha tanks were aiming for a church steeple on the visible horizon behind the cliffs. In order to maintain their line of sight it is believed that the tanks had to turn progressively away from the shore to combat the wavefronts pushing them down the beach, putting their sides virtually parallel with the waves/beach. This meant that the protective canvas flotation devices were easily swamped by the waves. If they had kept going directly forward with the front of the tank headed straight for the beach, they may have reached it.
Others believe that the error was on the part of the commanders aboard the ships from which the tanks were launched. They simply gave the order to launch too early, possibly to avoid getting too close to the battle themselves.
Operation Dragoon
The Operation Dragoon landings took place on 15 August, 1944. The invasion took place between Toulon and Cannes.
A total of 36 DD-tanks were used by three American tank battalions - the 191st, the 753rd and the 756th. The 756th battalion had eight tanks that were launched 2500 yards (2000 metres) from the beaches; one was swamped by the bow-wave of a landing craft and one sank after striking an underwater obstacle. The twelve tanks of the 191st battalion were all landed on or close to the beach. The 753rd battalion had 16 tanks, of which eight were launched at sea and successfully reached the shore and eight were landed directly on the beach later in the day.
The alternative: Deep Wading Gear
Although Duplex Drive allowed the landing craft to release the tank farther from shore, the alternative deep wading gear allowed a tank to drive partially or wholly underwater on the sea floor rather than swim. Deep wading Churchills took part in the 1942 Dieppe raid and deep wading tanks operated on D-Day also. Allied tanks were given waterproofed hulls and air intake and exhaust trunking to allow them to come ashore from shallow water. Tall ducts extended from the engine deck to above the turret top and these needed to stay above water. The front duct was the air intake for the engine and the rear duct vented the exhaust. This device saw use in many amphibious invasions, and was used on light tanks and tank destroyers as well. The US had similar devices for trucks and jeeps.
During the planning of Operation Sealion the Germans also developed tanks with the same purpose as the Sherman DD; to provide armoured protection to infantry during an amphibious assault. The Tauchpanzer III was a modified version of the Panzer III and, like the Sherman DD, was dropped from a landing craft around a mile off-shore. However, instead of floating the Tauchpanzer III drove on the sea-bed. A rubber hose supplied the engine and crew with air and gave the waterproofed tank a maximum diving depth of 15 metres (50 feet) making it an extreme example of a wading tank.
Many modern vehicles use similar devices (See Snorkel).
Surviving DD tanks
DD Valentine
A DD Valentine, restored to running condition, is in private ownership in Wolverhampton, England. The sunken wrecks of eight others, lost during training, are thought to exist in the Moray Firth; two have been located and are regularly visited by recreational divers.
There are also two Valentine DD tanks 3.5 miles out of Swanage Bay in Dorset. These tanks are 100 metres apart in 15 meters of water.
DD Sherman
The Bovington Tank Museum in England has a DD Sherman in working order, with its canvas flotation screens still intact.
Three of the DD Shermans lost on D-Day were salvaged in the 1970s. Two M4A1s are displayed at the Musée des Épaves Sous-Marine du Débarquement (Museum of Underwater Wrecks of the Invasion), a privately owned museum near Port-en-Bessin, in Normandy. An M4A4 recovered in 1971 is displayed as a monument at Courseulles-sur-Mer.
In 2000, there was an unsuccessful attempt by the US Navy to raise a sunken DD Sherman, located near Salerno in Italy. It was eventually recovered successfully on 18 May 2002. It has been restored and is on display in the Piana delle Orme museum near Latina, Italy.
A Sherman tank that was lost off the coast of Devon, UK was recovered in the 1980s, largely due to the efforts of a beachcomber named Ken Small. It is now on display in the village of Torcross as part of a memorial to those who died on 8 April 1944 when an invasion rehearsal, Exercise Tiger, was attacked by E-boats. This Sherman is a DD tank, this can be seen thanks to the specific gears to which the propellers were connected, under the rear deck of the tank. The metal frame on which was fixed the flotation screen disappeared because of the rust, but some traces of this frame can still be seen all around the hull.
An M4A2E8 HVSS Duplex Drive tank was exposed on the "Mile of Tanks" at Aberdeen for years, it is now stored on one of the Aberdeen Proving Ground storage yards .
A DD is part of the collection of the French tank museum, the Musée des Blindés. However, its turret appears to have been replaced at some point as it armed with a 76mm gun, only fitted to later versions of the Sherman.
See also
- T-37 tank - pre-World War 2, Soviet amphibious tank.
- T-38 tank - World War 2, Soviet amphibious tank.
- Type 2 Ka-Mi - World War 2, Japanese amphibious tank.
- Type 3 Ka-Chi - World War 2, Japanese amphibious tank.
- Allied Technological Cooperation During WW2
External links
- 14 April, 2005
- BBC online news 15 April, 2005
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- The First Hours of D-Day on Omaha Beach. Excerpted from Omaha Beachhead (6 June-13 June 1944) American Forces in Action Series. Historical Division. War Department (Washington, D.C.: Center of Military History, Facsimile Reprint, 1984), pp. 35-87. Available on-line at the ; also at the .
- Vaughan, Don. Neptune’s Treasures: A survey of ships and other craft lost during Operation Neptune. Available on-line at the .
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