DD tank
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The phrase DD tank is commonly used to refer to amphibious swimming tanks, mostly American M4 Sherman medium tanks, used in the 1944 Battle of Normandy. They were named after their "duplex drive" system. Swimming tracked LVTs already had operated in the 1942-43 Solomons campaign in the Pacific, swimming 2 1/2 ton trucks had operated in the 1943 invasion of Sicily, and swimming Ford jeeps also appeared in 1944--but 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 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 vehicles had been used, that American losses on the beaches of Normandy, particularly Omaha beach, would have been far less.
Development
Amphibious tanks were tested during the First World War, but none worked well enough to use in combat. Development continued during the interwar period. Amphibious tanks are generally of two kinds:http://www.d-daytanks.org.uk/articles/developing-tank.html 14 April, 2005- some with natural buoyancy, these were generally either too small to be useful or so large as to be impracticably bizarre.
- others were normal tanks with floatation added on, but these were too big to fit onto landing craft.
British Major General Percy Hobart applied Nicholas Straussler's folding screen design to Valentine and Tetrarch tanks. Hobart first tested the folding screen with a Tetrarch tank in Portsmouth Harbour. The test was successful and production was started using 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.BBC history ['D-Day - The Untold Story'] 14 April, 2005
By 1944, it was clear that the Sherman tank was more suitable for amphibious use 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 two propellers to the rear of the hull driven from the engine gearbox, and the addition of Straussler's flotation skirt around the hull.
DD Tanks could move at up to 4 knots (7 km/h) with the propulsion provided by the pair of propellers. The tanks were steered in the water by directing the propellers and a rudder. The flotation screen was a canvas curtain supported by 36 rubber tubes. These tubes were inflated with air to give the curtain rigidity. The canvas was attached to a metal frame welded to the tank's hull. The screen could be inflated in 15 minutes, and quickly deflated once the tank reached the shore.
Designs were even made to give the Cromwell and Churchill tank the DD treatment, but these were never finished. After the war the Centurion tank was tested with floatation screen and duplex drive. By the end of the 1950s development of DD tanks had ceased, as main battle tanks were becoming too heavy to be practically made amphibious, although work on amphibious light tanks continued in China and several nations have produced amphibious vehicles other than tanks.
Combat
The main use of DD tanks occurred on D-Day. Limited numbers were also used during Operation Plunder, the British crossing of the Rhine on March 23, 1945.
The DD Sherman was used to equip ten tank battalions of British, Canadian and American forces for the D-Day landings. Tank landing craft or LCTs, each carrying four tanks, would launch the DDs from around two miles offshore. They would swim to the beaches and overpower German defences 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.
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 and 32 out of 34 tanks successfully reached the beach, where they covered the assault troops as planned. This contributed to the comparatively light casualties on this beach.
On Gold Beach, the sea was rougher and the LCTs were ordered to land the tanks directly on the beach rather than risk launching them at sea. Consequently, instead of being the first units ashore, the DD's landed at the same time as the infantry and the other specialist assault tanks. German anti-tank guns caused heavy losses in some sectors of the beach but the assault was successful.
Only some of the Canadian DD tanks on Juno Beach, belonging to The Fort Garry Horse and the 1st Hussars, could be launched. Those assigned to the 7th Canadian Brigade, on the western end of the beach, were launched 800 yards (700 m) from the beach but only arrived after the first wave of infantry which consequently suffered heavy losses. However, the tanks were able to destroy German defensive positions and Canadian troops soon advanced several miles inland. 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.
On Utah Beach, four of the DD tanks were lost when their LCT struck a mine and sank. The remaining 28 arrived on shore successfully. However, on the way in, they were overtaken by the faster infantry landing craft and so only arrived 15 minutes after the initial infantry landing. Despite this, the DD tanks were one of several factors that contributed to the light American casualties on this 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.
In total, 27 tanks sank at sea. This is believed to be due to the fact that the sea was far rougher than optimum. 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 were released into the sea too far out,http://www.historylearningsite.co.uk/duplex_drive.htm 14 April, 2005 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. Many of the crews of these tanks drowned at sea BBC news ['The tanks that didn't land on D-Day'] 15 April, 2005. Although they were equipped with emergency breathing apparatuses capable of lasting 5 minutes, this was simply not enough in the turbulent sea. However, some did manage to radio back and warn following units not to launch as far out.
Until very recently it was believed that most the DD Shermans that were launched offshore of Omaha beach (from 741st Tank Battalion) were sunk immediately, swamped by the seas that were much higher than the operators had practiced with. It was also suggested that they were launched too far from shore. However, 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.
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 raidhttp://www.ospreypublishing.com/content1.php/cid=98 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.http://www.bbc.co.uk/ww2peopleswar/stories/12/a4817612.shtml
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
The Bovington Tank Museum in England has a complete DD Sherman and a DD Valentine, both with their canvas floatation screens still intact. The DD Valentine is still in running condition.A DD Sherman sunk in an exercise rehearsal off the coast of Devon, UK was recovered in the 1980s, largely due to the efforts of a beachcomber called Ken Small. It is now on display in the village of Torcross as part of a memorial to those who died in Exercise Tiger. http://www.history.navy.mil/faqs/faq20-2.htmhttp://www.shermantank.co.uk/
Three of the DD Shermans lost on D-Day were salvaged in the 1970's. One is 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. Another is displayed at the Juno Beach Centre, a museum dedicated to the Canadian contribution to D-Day, near 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.
See also
- T-38 - World War 2, Soviet amphibious tank.
- Type 2 Ka-Mi - World War 2, Japanese amphibious tank.
- List of "M" series military vehicles
References
- http://www.sproe.com/t/tank-dd.html 14 April, 2005
- [A new theory on the sinking of the floating Sherman tanks on D-Day]
- http://www.ospreypublishing.com/content1.php/cid=98
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