Concrete boats, tanks that float and the army that never was

The D Day landings were and still are the biggest amphibious assault ever staged. The planning for the invasion took months and new ideas were tested in secrecy in advance of the invasion. Although the Germans knew that a landing was inevitable they had to be kept guessing about it’s whereabouts until the last moment possible.

The 1942 raid on Dieppe that cost so many Allied lives with no obvious gain has been a bitterly argued exercise ever since. If anything came from the failure it was the awareness that new ideas needed to be developed in order to overcome the problems encountered

Capturing a working port on the European coast would be difficult if not impossible and potentially crippling in terms of loss of life yet somehow men and supplies would need to be constantly brought ashore in order to back up the first wave of invaders and to keep the advancing armies supplied.

The simple solution if no suitable harbour could be captured was to bring the components of a temporary shelter with the invasion fleet. And thus the Mulberry project was begun

During World War One Churchill had drafted detailed plans for the capture of two islands, Borkum and Sylt, which lay off the Dutch and Danish coasts. He envisaged using some flat-bottomed barges, or caissons, measuring 37m x 23m x 12m which would form the basis of an artificial harbour when lowered to the seabed and filled with sand. Events moved on and Churchill’s proposal was filed away and was never published.

In 1941, Hugh Iorys Hughes, a quiet, unassuming Welshman from North Wales, had similar ideas. He was a successful civil engineer living in London when he submitted plans to the War Office. Their potential value was not recognised until Hughes’ brother, a Commander in the Royal Navy, drew the plan to the attention of more senior officers. This intervention brought Hughes and his ideas to the fore. It was to be the beginning of a long association with the Mulberry project.

Various designs were tried and tested before settling on a combination of large floating concrete caissons to provide breakwaters and floating steel roadways to connect to shore. Mountbatten’s ideal specification was for a pier a mile long that could withstand gale force winds and be capable of berthing large coasters. To do this, the artificial harbours would need to provide sheltered conditions and be larger than the port of Dover which had taken seven years to build in peacetime! Within the sheltered areas, stable floating quays would be located some distance from the beaches to provide sufficient water depth (6.7 meters) for the docking vessels. These quays would be linked to the beaches by floating roadways to allow the discharged goods and equipment to be transported ashore in fleets of lorries. Two harbours would be required – Mulberry A for the USA beaches of Omaha and Utah and Mulberry B for the British and Canadian beaches of Gold, Juno and Sword. The designs would allow for the floating caissons to be secured in place in four days. Each harbour would have a capacity of 7000 tons of vehicles and supplies per day.


Two of the concrete caissons can be seen in Portland harbour today and nearer to our HQ, one lies broken backed in Langstone Harbour, just off the ferry pontoon at Hayling Isand and one is an easy and fascinating dive 10 metres down off Selsey. The Hayling caisson is one of four built south of the Ferry Boat Inn (launch ramps can still be seen) and materials were brought onto the island via the now defunct Hayling Billy line. It is rumoured that the builder charged with the construction skimped on materials hence the break-up of one of the four caissons built

The scale of the project was enormous and was in danger of over-stretching the capacity of the UK’s civil engineering industry. From late summer of 1943 onwards three hundred firms were recruited from around the country employing 40,000 to 45,000 personnel at the peak. Men from trades and backgrounds not associated with the construction industry were drafted in and given crash courses appropriate to their work. Their task was to construct 212 caissons ranging from 1672 tons to 6044 tons, 23 pier-heads and 10 miles of floating roadway.

The results of such a massive construction project needed to be disguised or hidden. The caissons had sea-cocks that could be opened and allowed them to sink in a controlled manner, ready for air to be pumped in when they were ready to be used. The submerged unit at Selsey was raised and then the order countermanded. The caisson had swung on the tide and settled across the hole its weight had previously created. It too broke its back and now is a haven for marine life and an excellent beginners’ dive.

A large number of British and USA tugs were requisitioned to tow the Mulberries from their assembly point near Lee-on-Solent to France. Operation Corncob got underway when the first of the tugs set off on June 4 later to hold their position in mid channel when D-Day was delayed by a day. When the invasion finally got underway most caissons were positioned about 5 miles off the French coast.On D+1 the caissons, each with a 4 man crew, two sailors and an anti-aircraft gun emplacement, were towed to positions about a mile off-shore and handed over to a fleet of powerful harbour tugs which manoeuvred them into their final positions. The caissons’ sea valves were opened until they settled at previously agreed depths. Each Mulberry was about a mile long and stood about 30 ft (9m) above sea level at low tide and 10 ft (3m) at high tide. The block-ships at Mulberry B were all in position by June 13th and formed two crescent shaped harbours which accommodated 75 Liberty ships and small craft.


Mulberry A was in use for less than 10 days when, on June 19, it was severely damaged by the worst period of sustained severe weather for 40 years. Out of 31 caissons laid in position 21 were damaged beyond repair with broken backs and sides. Mulberry A was never used again and parts of it were scavenged to repair damage to Mulberry B. The Americans quickly reverted to the traditional methods of unloading from landing craft and DUKWs directly onto the beaches often coming in on one tide and leaving on the next. Such was their success that on occasions they exceeded the impressive performance achieved at Mulberry B.

Each day around 9000 tons were landed via Mulberry B until the end of August by which time Cherbourg port became available for use at least in part and, towards the end of the year, after the capture of Walcheren, the port of Antwerp. Mulberry B was in use for 5 months during which time over 2 million men, half a million vehicles and 4 million tons of supplies passed through the harbour.




In Studland Bay are seven Valentine swimming tanks that failed to reach shore. The concept of amphibious tanks had been around since almost the birth of the vehicle, experiments were made with a British MkIX in 1918. Hungarian born Nicholas Straussler developed a floatation screen for tanks in 1940 and after successful tests on a Tetrach in 1941 ( in the same reservoir that had seen the 1918 test) sea trials were satisfactorily undertaken near Hayling Island.


Another of Straussler’s wartime projects was the Straussler Conversion. This was an experimental modification of the Ordnance QF 17 pounder and Ordnance QF 32 pounder anti-tank guns. The guns were fitted with motorized gun-carriages. A modified ammunition limber would be attached to the gun’s trails, effectively making a four-wheeled, self-propelled vehicle and removing the need for a truck to tow the gun. The idea of equipping large artillery pieces with engines, to give a limited amount of independent mobility, would be eventually adopted post–war with guns like the Anglo / German / Italian FH-70

450 Valentine tanks were made with the flotation screen and a propeller driven from the main engine (Duplex Drive). These were used for crew training for those who subsequently served in DD versions of the M4 Sherman, one of a number of unusually modified, special purpose tanks that saw action during and after D-Day. As an aside two of the Studland Bay Valentines are diveable having suffered least after being blown up by the Navy after someone brought live ammunition ashore from them and flashed it around on Poole Quay. They make an excellent little enclosed eco system on an otherwise barren sea floor.


By the time of preparations for D Day the Sherman was in production and modifications to the base tank 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 3 ft (0.91 m) 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 4 knots (4.6 mph; 7.4 km/h).[3] 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.


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, also known as Landing Craft, Tank (LCT). 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 120 feet (37 m).

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 6 ft (1.8 m) 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 3 mi (4.8 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 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. There has been a suggestion that the Omaha tanks were aiming for a church steeple on the visible horizon behind the cliffs and in order to maintain their line of sight 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.

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 2.5 miles (4 km) from shore. Five could not be launched as the leading tank on its LCT tore its screen – they were later landed directly on shore – one tank sank after being struck by an LCT.




How do you convince the enemy that the landing is going to be at a point other than where you will actually land? Make a noise about it, accidentally let information slip and have a massive army assemble in an area close to the fictitious landing site.

Northern France was the obvious target, but the Allies had other options, too. So, once they settled on northern France, it became their goal to lead the German high command—especially Hitler—to believe they would do the unexpected and land somewhere else. British intelligence agencies set to work, launching an enormous deception campaign called Bodyguard, designed to make the Germans believe the invasion might come in Greece, on the Adriatic coabadge1st of Yugoslavia, in the south of France, on the Biscay Bay coast of France, through the Low Countries, or via Norway and Denmark. And so, with the help of agents turned by the “double cross” system, tanks and landing craft carelessly visible to aerial reconnaisance and a great deal of radio traffic the First US Army Group prepared to cross the Straits of Dover.


In one instance an English farmer could see that sometime overnight a column of Sherman tanks had parked on his field. One of his bulls also noticed the American tanks and was eyeing one of them warily. Suddenly, the bull lunged. The farmer braced himself for the sight of one of his prized bovines cracking its skull against armor plating. The bull struck the tank at top speed, and with a lazy hiss of air, the Sherman deflated into a pile of olive-drab rubber sheeting. The bull and the farmer had stumbled onto Operation Quicksilver, one of the most elaborate deceptions in the history of warfare: the creation of a phantom army to divert attention from the real Allied army poised to invade France in the spring of 1944.The landing craft were also dummies and the radio traffic typical of a large army group was generated by a few signallers moving around the East Anglian countryside in telecommunications vans.


badge2FUSAG was activated in London in 1943 as the planning formation for the Allied invasion of France under General Omar Bradley. When Twelfth United States Army Group was activated on 1 August 1944, Bradley and his staff transferred to the headquarters of the new army group. Despite a lack of personnel, FUSAG continued to exist on paper as part of the deception of Operation Quicksilver. In order to make the German forces believe the Allied invasion would come at Pas de Calais, the phantom force was stationed at Dover, directly across the English Channel from the site. To further attract the Axis commanders’ attention, General Dwight D. Eisenhower placed George S. Patton in command of the phantom force and increased the formation’s apparent size to be larger than the British-led 21st Army Group under Bernard Montgomery. Patton was considered by the Germans to be a formidable offensive commander; he was temporarily unemployed as punishment for slapping a battle-fatigued soldier in Sicily.



Even in Britain the exact site of the invasion remained a closely guarded secret. When two men from arrived at Southwick House (north of Portsmouth) from Chad Valley, the toy and jigsaw manufacturers tasked with providing a map of Northern Europe for the allied headquarters, they were escorted into the map room. Although their gigantic map showed the entirety of the lands from Norway to Southern Spain only the section for Northern France was installed, the rest was burnt. The workmen were then detained incommunicado and given jobs around the building and grounds until well after the invasion became reality.

At first, the force referred to as Army Group Patton was a phantom army composed of real units (earmarked for the command of British Lieutenant General Bernard Montgomery, but for the time being appearing in the FUSAG order of battle) and wholly fictional divisions and corps. This created the impression that the British, Canadian, and American armies gathering in England were as much as 70 percent bigger than the actual number of soldiers preparing to embark for France. Their locations in East Anglia and southeast England made it seem that the Allies were planning to go for broke and push across the narrowest part of the English Channel in a bold and costly attempt to take the port of Calais intact. If the Quicksilver operatives could pull off this imposture convincingly, the Germans would have little choice but to keep heavy forces in the Pas de Calais, even if Allied troops landed elsewhere on the French coast.


The deception worked so well that significant German forces remained in the Pas de Calais region for seven weeks after the real invasion at Normandy to defend against what they thought would be the true invasion force.

Agents infiltrated by Germany into the United Kingdom who became double agents acting for Britain in the Double Cross System played a vital role in persuading the Germans that FUSAG was real. After it had become clear that Normandy, not Calais, was the invasion site, to preserve the credibility of the Double Cross network’s agents in spite of the totally false information they had persuaded the Germans to believe, the Germans were persuaded that FUSAG had been real, but had been disbanded and attached to the forces at Normandy because the Normandy “diversion” had been so successful that the Calais landing had become unnecessary.