DD tank DD or Duplex Drive tanks , nicknamed " Donald Duck tanks " , were a type of amphibious swimming tank developed by the British during the Second World War . The phrase is mostly used for the Duplex Drive variant of the M4 Sherman medium tank , 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 enabled it to float , and had a propeller powered by the tank ' s engine to drive them in the water . 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 . History . Early 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 . As tanks are heavy for their size , providing them with enough buoyancy was a difficult engineering problem . Designs that could float unaided were generally small and light with thin armour , such as the Soviet T - 37 . Heavier vehicles , such as the experimental , British AT1 * had to be so large that the design was impractical . The alternative was to use flotation devices that the tank discarded as soon as it landed – the approach adopted by the Japanese with their Type 2 Ka - Mi and Type 3 Ka - Chi amphibious tanks . 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 . The system was unsatisfactory in other ways , due mainly to the unwieldy bulk of the floats that were big enough to float a tank – these were each roughly the size of the tank itself . In practice , there would be severe difficulties in transporting 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 from an off - shore landing craft , making their use in amphibious landings impractical . In 1940 , Straussler solved the problem by devising the flotation screen – a device which folded and was made of waterproofed canvas . The screen covered the top half of the tank effectively creating a canvas hull , greatly increasing the vehicle ' s freeboard , and providing 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 flotation screen was a redundant Tetrarch light tank provided to Straussler . Its first trial took place in June 1941 in Brent Reservoir ( also known as Hendon Reservoir ) in north London in front of General Sir Alan Brooke ( at the time General Officer - in - Command Home Forces ) . The reservoir had been the location where trials of the floating version of the World War I , Mark IX tank took place , 23 years earlier . Satisfactory sea trials of the Tetrarch took place in Portsmouth Harbour . A prototype of a Duplex Drive Valentine tank began trials in 21 May 1942 , although it subsequently sank ( possibly during a trial in which it was subject to machine gun fire ) . In June 1942 , permission was given by the Ministry of Supply for the manufacture of 450 Valentine DDs . It later became clear that the Sherman was more suitable for use with a screen than the Valentine and the DD screen was adapted for the Sherman by April 1943 . One reason for this was that the Sherman could move in the water with its gun forward ready to fire as soon as land was reached . The Valentine was also an older and generally inferior design . Valentine DDs were used for training and the majority of the American , British and Canadian DD crews did their preliminary training with them , which incurred several losses . The sunken wrecks of at least 10 are known to lie off the British coast . Sherman DD . Modifications to the Sherman included the 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 flotation screen was attached to a horizontal mild steel boat - shaped platform 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 practice there was about of freeboard . 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 . In practice , some units kept the flotation 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 ( gearbox at the front ) 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 . 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 from a platform at the rear of the turret , where he could see over the skirt , could contribute by operating a large tiller . Experience from D - Day led to an improved , Mark II version of the DD Sherman . The screen was extended and strengthened by fixing to the turret , 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 . The first DD Shermans produced by the British were used by both British and US units . Later production was by both the US and the UK . British Shermans were Sherman III ( M4A2 ) and Sherman V ( M4A4 ) conversions . The US used the M4A2 only for their conversions . Later flotation screen use . Designs were made to give the Cromwell and Churchill the DD treatment , but these were never completed . 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 . The trailer , in the water , was supported by an inflatable flotation device . After the war , the Centurion was tested with a flotation screen and duplex drive . By the end of the 1950s , development of DD tanks had ceased , partly because main battle tank s were becoming too heavy to be practically made to swim – although experiments were carried - out in the mid - 1960s with a floating Centurion that used a similar system , but with rigid panels instead of a flexible screen . The 38 tonne Vickers MBT was fitted with a flotation screen that allowed it to swim . 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 . 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 ; 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 sent to India , the 25th Dragoons were trained in their use , but planned operations against the Japanese in Malaya never occurred . D - Day . The DD Sherman was used to equip eight tank battalions of American , British , and Canadian forces for the D - Day landings . They were carried in Tank landing craft ( LCT ) s . These could normally carry nine Shermans , but could fit fewer of the bulkier DDs . British and Canadian LCTs carried five tanks , the Americans carried four as their LCTs were shorter at about . The DDs would typically be launched around two miles from the shore , swim to the beaches and overpower the German defences . The tank ' s record was a mixture of success and failure , although they are mainly remembered for their disastrous performance on Omaha Beach . Sword Beach < br > 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 from ' A ' and ' B ' Squadrons of 13th / 18th Royal Hussars were launched from shore . Five could not be launched as an LCT ' s leading tank tore its screen – they were later landed directly on shore – one tank sank after being struck by an LCT . Gold Beach < br > On Gold Beach , the sea was rougher . The tanks of the Sherwood Rangers Yeomanry were launched late , about 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 . Sea conditions meant the tanks of ‘ B ’ and ‘ C ’ Squadrons , from the 4th / 7th Royal Dragoon Guards were landed in the shallows . They then drove onto the beach with their screens up so they would not 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 < br > On the Canadian Juno Beach , The Fort Garry Horse and the 1st Hussars were equipped with DDs , but only those of the 1st Hussars could be launched . They were assigned to the 7th Canadian Brigade , at the western end of the beach . Some of the tanks were launched at and some at 800 yards ( 700 m ) ; twenty - one out of twenty - nine tanks reached the beach . The 8th Canadian Brigade , at 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 DDs were operated by the 70th Tank Battalion . Armoured support was reduced by four DDs when their LCT was lost to German artillery fire . The remaining tanks were launched 15 minutes late from the beach . Twenty - seven out of twenty eight reached the beach but confusion caused by the massive smoke screen meant they landed around from their aiming point and saw little German opposition . Omaha Beach < br > At Omaha Beach almost all of the tanks launched offshore were lost , contributing to the high casualty rate and sluggish advance from that beach . One hundred and twelve tanks were assigned to the first wave at Omaha Beach , with 56 tanks in each of the 741st and 743rd Tank Battalion s . Each of these battalions had 32 DD and 24 other Shermans ( including many Sherman bulldozers for clearing obstacles ) . Starting at about 0540 , the 741st Tank Battalion put 29 DDs into the sea , but 27 of these sank , the remaining 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 vehicles of the 741st Tank Battalion and all tanks of the 743rd Tank Battalion , ( except for the four aboard one LCT that was hit by artillery fire just off the beach ) , were landed directly on the beach , starting at about 0640 . DD Tanks were designed to operate in waves up to 1 foot ( 0 . 3 m ) high ; however , on D - Day the waves were up to high . These were much worse conditions than the tanks had been tested in and hence they were swamped . Also , the tanks of 741st Tank Battalion were launched too far out , about 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 DSEA emergency breathing apparatus capable of lasting 5 minutes , the tanks were also equipped with inflatable rafts . Some sources claim that these life - saving measures were ineffective ; this was contradicted by the testimony of survivors . Most of the crews were rescued , mainly by the landing craft carrying the 16th 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 the 741st Tank Battalion were sunk almost immediately . Some stayed afloat for a matter of minutes ; according to the crews one tank swam for 15 minutes , 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 waves pushing them down the beach , putting their sides virtually parallel with the shoreline . This meant that the canvas flotation devices were easily swamped . 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 due to 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 possibility of disembarking the tanks directly onto the beach if the sea was too rough had been discussed and agreed upon by Colonel Skaggs and Colonel Upham , ( commanding officers of the 741st and 743rd battalions ) , before the tanks left Portland , England . Operation Dragoon . The Operation Dragoon landings took place on 15 August 1944 between Toulon and Cannes in southern France . A total of 36 DD tanks were used by three American tank battalions – the 191st , the 753rd and the 756th . The 756th had eight tanks that were launched 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 . Five of the C Company tanks of the 191st were immobilized by mines . The 753rd battalion had 16 tanks , of which eight were launched at sea and successfully reached the shore , eight were landed directly on the beach later in the day . Northwest Europe . The Staffordshire Yeomanry were converted to DD tanks after D - Day and trained with them in Belgium . On 26 October 1944 , they undertook a 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 they had great difficulty in landing – 14 became bogged down in mud and only four were available for action . Operation Plunder , the Rhine crossing , began on the night of 23 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 , mats at the objective points ( carried across beforehand by LVT s ) allowed the DDs to climb the steep , muddy banks of the river . The DD ' s last combat swimming operation was the Staffordshire Yeomanry ' s crossing of the River Elbe at Artlenburg on 29 April 1945 . Italian campaign . By February 1945 , the 7th Queen ' s Own Hussars in Italy had been trained and equipped with DD tanks , both Shermans and Valentines . DD Shermans were successfully used in the crossing of the Po River on 24 April . On 28 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 known 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 , making the tanks useful troop transports . " T - 6 Device " . An alternative to the DD was the " T - 6 Device " , developed by the US Army . Limited numbers of the " T - 6 Device " were used by the US Army and Marines during Landings at Okinawa . Battle of Okinawa The " T - 6 Device " kit consisted of a structure of box - like , pressed - steel floats ( pontoons ) mounted on the front , rear and sides of a Sherman . Propulsion was provided by the rotation of the tracks . No propellers . The front and rear floats were discarded on the beach , some in the water . Explosive bolts were used . Side floats were removed from the tanks on shore when the tactical situation permitted . In an oral interview with former Pvt . Maurice Dean Derby 37699146 , Browning Automatic Rifleman , Co . A , 17th Infantry Regiment , 7th Infantry Division , He related that " On the night of the landing ( Okinawa , 1 April 1945 ) we were kept awake all night because the Tank Crews were beating on the pontoons with sledgehamers to remove them from the Tanks " The tanks were Co . B , 711 Tank Battalion . Compared with the DD , the floats were bulky and harder to stow , limiting the number of tanks that could be carried in a landing craft . The system was more seaworthy however and had the advantage of allowing the Sherman to fire its main gun as it approached the beach . The Sherman ' s gyroscopic gun stabilization allowed accurate fire even if the tank was being pitched by waves . German equivalent . During planning for an invasion of England in 1940 ( Operation Sea Lion ) , the Germans also worked on developing amphibious tanks capable of directly supporting infantry during a beach assault . The Schwimmpanzer II was a modified version of the Panzer II which , at 8 . 9 tons , was light enough to float with the attachment of long rectangular boxes to either side of the tank ' s hull . The boxes were made of aluminum and filled with Kapok sacks to preserve buoyancy if water leaked into the pontoons . Motive power came from the tank ' s own tracks which were connected by rods to a propeller shaft running through each float . The Schwimmpanzer II could make 5 . 7 km / h in the water . An inflatable rubber hose around the turret ring created a waterproof seal between the hull and turret . The tank ' s 2 cm gun and coaxial machinegun were kept operational and could be fired while the tank was still churning its way ashore . Schwimmpanzer IIs were deployed from a specially modified landing barge ( Type C ) and could be launched directly into open water from a hatch cut into the stern . The Germans converted 52 of these tanks to amphibious use prior to Sea Lion ' s cancelation . Instead of floating , the Tauchpanzer , a modification of the Panzer III and Panzer IV , 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 making it an extreme example of a wading tank . The Germans converted 168 Panzer IIIs and 42 Panzer IVs for use in Operation Sea Lion . Surviving DD tanks . 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 in the Moray Firth in Scotland ; two have been located and are regularly visited by recreational divers . Two sunken Valentine DDs rest 3 . 5 miles out of Swanage Bay , Dorset . These tanks are 100 metres apart in 15 meters of water . References . Notes Bibliography