DD tank

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DD tank
DD Sherman tank with its flotation screen lowered
Service history
In service	1944–1950s
Used by	United Kingdom, Canada, United States
Wars	World War II
Production history
Designer	Nicholas Straussler
Designed	1941–44
Variants	DD Valentine, DD Sherman
Specifications
Speed	4 knots (7 km/h) swimming

DD tanks (for Duplex Drive, but nicknamed Donald Duck tanks) were a type of amphibious swimming tanks developed by the British during the Second World War. The phrase is mostly used for the Duplex Drive variant of the M4 Sherman medium tanks, that was used by the Western Allies during and after the Normandy Landings in June 1944.

DD tanks worked by erecting a 'flotation screen' around the tank, which would enable it to float, and had a 'Duplex Drive' water screw driven from the tank's engine.

The DD tanks were one of the many specialised assault vehicles, collectively known as Hobart's Funnies, devised to support the planned Invasion of Europe.

[edit] History

[edit] Early Development

Diagram of a floatation screen fitted to a Tetrarch tank, taken from Straussler's patent, U.S. Patent 2,390,747, 1940

reptile 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.

As tanks are heavy for their size, providing them with enough buoyancy to float was a difficult engineering problem. Designs that could float unaided were generally small, light vehicles with thin armour, such as the Soviet T-37 tank. Heavier floating tanks, such as the experimental, British AT1* had to be so large to give them buoyancy that the design was impractical^[1].

The alternative was to use attached floatation devices that the tank discarded as soon as it landed. In Britain, the Hungarian-born engineer Nicholas Straussler developed collapsible floats for Vickers-Armstrong that could be mounted on either side of a light tank to make it amphibious. Trials conducted by the British War Office showed that such a tank, propelled by an outboard motor, 'swam' reasonably well^[2].

Valentine DD tank with screen lowered and gun pointing towards the rear of the vehicle.

The system was unsatisfactory, mainly because of the unwieldy bulk of floats that were big enough to float a tank (each was roughly the size of the tank itself). In practice, there would be severe difficulties in transporting by truck enough floats, even collapsed ones, to move a large unit of tanks across a body of water. Also, such floats made a tank too wide to launch itself into the sea from an off-shore landing craft, making their use in amphibious landings impractical.^[3]

In 1940, Straussler solved the problem by devising the floatation screen - a folding screen made of waterproofed canvas. The screen covered the top half of the tank and provided buoyancy in the water. When collapsed, it would not interfere with the tank's mobility or combat effectiveness.

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^[2] 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.

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. The Vaentine DD's were used for training and the majority of the American, British and Canadian DD tank crews did their preliminary training with them, which incurred several losses.^[4] The sunken wrecks of at least 10 are known to lie off the British coast.

[edit] Sherman DD

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 base of the canvas floatation screen was attached to a horizontal 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 ^[2] although, in practice, some units kept the floatation equipment and their tanks were used in several amphibious operations.

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 directly from the gearbox to the propellers. 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 (4.6 mph; 7.4 km/h)^[2]. Both the commander and the driver could steer in the water, although with different methods. 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.

Experience from D-Day lead to an improved, Mark II version of the DD Sherman. The screen was extended and strengthened, a new type of bilge pump fitted and a second set of hydraulic steering controls was fitted at the commander's station, although his tiller was retained. An air compressor replaced the air cylinders that provided the pressurized air to erect the screen.^[5]

[edit] Later Floatation Screen Use

M2 Bradley Infantry Fighting Vehicle emerging from the water (1983). This M2 uses a screen but is not DD.

Designs were 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.^[6]

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-1960s with a floating Centurion that used a similar system, but with rigid panels instead of a flexible screen.^[7]

Medium and light vehicles continued to be made amphibious by the use of flotation screens into the 1980s, 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.

[edit] Combat

Men of No. 4 Commando engaged in house to house fighting with the Germans at Riva Bella, near Ouistreham. Sherman DD tanks of 'B' Squadron, 13/18th Royal Hussars are providing fire support and cover, 6 June, 1944

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, Operation Plunder, the British crossing of the Rhine on 23 March 1945 and in several operations on the Italian Front in 1945. DD Tanks were send to India and the 25th Dragoons were trained in their use, but planned operations against the Japanese in Malaya never occurred.^[8]

[edit] 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 ^[2]. British and Canadian LCTs carried five tanks, the Americans carried four DD's as their LCT's were shorter at about 120 feet (37 m).

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 2.5 miles (4,023 m) 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 (640 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.^[2]

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 (3,658 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

DD tanks on 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.^[2] The remaining tanks were launched 15 minutes late at a point 1,000 yards (914 m) 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 (1,829 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,^[9] about 3 miles (4,828 m) 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.^[10]. Some sources claim that these life-saving measures were ineffective,^[11] contradicted by the testimony of survivors.^[10] Most of the crews were rescued, mainly by the landing craft of the 16th RCT (Regimental Combat Team)^[12] although five crewmen are known to have died during the sinkings.^[10]

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"^[10] Tanks at the other four beaches suffered no such problems. New research^{[by whom?]} suggests that the Omaha tanks were aiming for a church steeple on the visible horizon behind the cliffs.^{[citation needed]} 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.^{[citation needed]}

Others believe that the error was on the part of the commanders aboard the ships from which the tanks were launched.^[who?] They simply gave the order to launch too early, possibly to avoid getting too close to the battle themselves.^{[citation needed]}

[edit] 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.^[2] The 756th battalion had eight tanks that were launched 2,500 yards (2,286 m) 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.

[edit] North West Europe

Sherman DD tanks crossing the Rhine, 24 March 1945

The Staffordshire Yeomanry were converted to DD tanks after D-Day and trained with them in Belgium. On the 26th of October 1944, they undertook a 7-mile (11 km) swim across the Western Scheldt to attack South Beveland, during the Battle of the Scheldt. The DD Tanks' longest operational water crossing took place without casualties, but the tanks had great difficulty in landing - 14 became bogged down in mud and only four were available for action.^[13]

Operation Plunder, the crossed the Rhine, began on the night of the 23rd of March, 1945. As well as the Staffordshire Yeomanry, DD tanks equipped the American 736th and 738th Tank Battalions and the British 44th Royal Tank Regiment. Some tanks were lost in the river, but the crossings were considered a success. The tanks were launched from points upstream from their objectives, to take account of the Rhine's strong current, and mats at the objective points (carried across beforehand by LVTs) allowed the DDs to climb the steep, muddy banks of the river^[13].

The DD's last combat, swimming operation was the Staffordshire Yeomanry's crossing of the River Elbe at Artlenburg on the 29th of April 1945^[13].

[edit] Italian Campaign

By February 1945, the 7th Queen's Own Hussars in Italy had been trained an equipped with DD tanks, both DD Shermans and DD Valentines. DD Shermans were successfully used in the crossing of the Po River on the 24th of April. On the 28th of April, those tanks still able to swim were used in an assault across the River Adige. During this operation, Valentine DDs were used to transport fuel (their only know use on active service). The tanks continued to be used in combat in the advance towards Venice. There were no further swimming operations, but it was found that the folded flotation screen offered a large seating area, that made the tanks useful troop transports.^[14]

[edit] The alternative: deep wading gear

Deep wading gear on a Sherman in Normandy, 1944.

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^[15] 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.^[16]

German Tauchpanzer III under test (1940).

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 (49 ft) making it an extreme example of a wading tank.

Many modern vehicles use similar devices (See Snorkel).

[edit] Surviving DD tanks

[edit] 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. Two sunken Valentine DD's rest 3.5 miles out of Swanage Bay, Dorset. These tanks are 100 metres apart in 15 meters of water. ^[17]

[edit] DD Sherman

Surviving DD Sherman in the Bovington Tank Museum, including canvas flotation screen

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.

One of these recovered tanks, along with a variety of personal items recovered with it, has been purchased by an American company, Overlord Research, LLC, based in West Virginia. The owners intend to return the tank to the United States, preferably for public display in an American Museum such as the D-Day Museum in New Orleans, Louisiana or the National Museum of the United States Army, to be constructed at Fort Belvoir, Virginia. However, the details of the repatriation of the DD Tank and its final location in the United States are still being determined. As the tank was submerged for many years, Overlord believes preservation of its current condition which shows its loss at sea as it approached Omaha Beach is an aspect which is more historically important than attempting a restoration.

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 [1] 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 [2].

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 76 mm gun, only fitted to later versions of the Sherman.

A DD tank is displayed in India, at the Indian Armoured Corps Museum in Ahmednagar Fort, Ahmednagar.

[edit] See also

Wikimedia Commons has media related to: DD tank

• T-37 tank - 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

[edit] References

[edit] External links

• http://www.sproe.com/t/tank-dd.html 14 April, 2005
• BBC online news 'The tanks that didn't land on D-Day' 15 April, 2005 A new theory on the sinking of the floating Sherman tanks on D-Day
• http://www.ospreypublishing.com/content1.php/cid=98
• Juno Beach - Fort Garry Horse DD Tanks on D-Day
• Juno Beach - 1st Hussars DD Tanks on D-Day
• 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 Sam Houston State University website; also at the the official US Army website (www.army.mil).
• Vaughan, Don. Neptune’s Treasures: A survey of ships and other craft lost during Operation Neptune. Available on-line at the Military Officers Association of America (MOAA) website.