D-Day’s Forgotten Critical Secret Weapon

In the early morning hours of June 6, 1944, a massive armada of more than 5,000 ships and 1,200 aircraft appeared off the coast of Normandy in northern France. Moments later, some 160,000 American and British Commonwealth troops stormed onto the beaches or landed by parachute behind enemy lines. Operation Overlord, the Allied invasion of Nazi-occupied Europe, had begun. The largest amphibious assault in military history, the D-Day landings, more on what D-day actually stands for in the Bonus Facts later as most people get this wrong, were an incredibly complex operation, and its planners left little to chance. Attacks were planned and rehearsed down to the smallest detail; specialized vehicles like swimming, flame-throwing, and mine-clearing tanks devised; and an elaborate deception campaign involving inflatable tanks, captured spies, and entire phantom armies mounted to fool the Germans into thinking the invasion would take place elsewhere. Yet despite all these careful preparations, Overlord may well have failed were it not for an often overlooked innovation: an ingenious portable harbour that could be assembled in days and allow hundreds of thousands of tons of cargo to be unloaded onto the beaches.
Perhaps more than any ship, plane, or tank, this remarkable engineering achievement allowed the Allies to sustain the momentum of the invasion and secure a foothold – and ultimately victory – in Europe. This is the story of the Mulberry Harbour, the unsung secret weapon of D-Day.

When the first preparations for what became Operation Overlord began in late 1942, Allied planners faced a daunting task. On March 23, 1940, Adolf Hitler had issued Directive 40, ordering the construction of a massive line of defences along the western coast of Europe to stave off a possible Allied invasion. By mid-1944, this so-called “Atlantic Wall” stretched 3,200 kilometres from the northern tip of Norway to the Spanish border and included more than 15,000 reinforced concrete emplacements bristling with large-calibre guns. Among the largest engineering projects in human history, the Atlantic Wall swallowed some 1.2 million tonnes of steel and 17 million cubic metres of concrete – much of it poured by 260,000 forced labourers of the infamous Organisation Todt. The artillery emplacements and machine gun bunkers, built with interlocking fields of fire and manned by a garrison of 300,000 troops, were further reinforced by millions of land mines and fearsome steel obstacles designed to halt any invading force before it could even clear the beach. The most heavily-defended sections of the wall were the festungen or “fortresses”, which included all the major Atlantic ports like Antwerp, Cherbourg, and Brest. The capture of such a port was vital to the success of any invasion, allowing the Allies to offload the vast amount of men, vehicles, ammunition, fuel, food, and other materiel needed to sustain the subsequent breakout.

But capturing such a port would be extremely costly – a fact the Allies had learned the hard way. In the early morning hours of August 19, 1942, 5,000 men of the Canadian 2nd Infantry Division and British Army Commandos carried out Operation Jubilee, a large-scale amphibious raid against the French port city of Dieppe. Right from the start, everything that could go wrong, did. While sailing across the English Channel, the raiding force ran into a patrol of German torpedo boats, ruining the element of surprise. Thus alerted, the troops defending Dieppe were ready and waiting, and rained withering fire down onto the landing troops from the sheer, horseshoe-shaped cliffs overlooking the town. Tanks struggled to advance up the shingle beach, their tracks spinning uselessly over stones round as ball bearings. One by one they were picked off by German guns, with none reaching the town or making it back to England. Meanwhile, Luftwaffe aircraft sunk dozens of Allied landing craft and made mincemeat of the raider’s RAF air cover. By the time the raiders withdrew ten hours later, more than 1,700 had been killed, 2,500 wounded, and 1,960 captured – an atrocious casualty rate of nearly 68%. 33 landing craft and one destroyer had also been sunk and 106 aircraft shot down. Operation Jubilee was a complete disaster, achieving few of its aims and demonstrating the folly of trying to capture a heavily-defended port from the sea. A full-scale invasion of Europe would require a different approach. As Royal Navy Commodore John Hughes-Hallett noted while steaming home from Dieppe:

“Well, if we can’t capture a port, we will have to take one with us.”

This was far from a new idea. In 1917, Winston Churchill – then First Sea Lord of the Royal Navy – devised a unique plan for invading the East Frisian Islands of Borkum and Sylt in the North Sea. The plan involved sinking a series of flat-bottom barges off the coast to form an artificial harbour, allowing men, vehicles, and supplies to be efficiently brought ashore. Churchill was very aware of how poor logistics and a lack of momentum could doom an amphibious assault, having planned the disastrous Gallipoli campaign in which Entente forces became pinned down on the Turkish coast and suffered nearly 200,000 casualties over an eight-month battle. Unfortunately, the strategic situation changed before Churchill could implement his Frisian Islands plan, and the scheme was quickly forgotten.

It was not until early in the Second World War that the idea of using an artificial harbour for an amphibious assault was finally resurrected. In 1941, the British War Office established a special department to evaluate various designs. The department was placed under the command of Combined Operations Headquarters, an inter-service organization tasked with carrying out special military operations on enemy territory.

According to General Dwight D. Eisenhower, Supreme Commander of the Allied Forces:

“The first time I heard this idea [Mulberry] tentatively advanced was by Admiral Mountbatten in the spring of 1942. At a conference attended by a number of service chiefs, he remarked, ‘If ports are not available, we may have to construct them in pieces and tow them in.’ Hoots and jeers greeted his suggestion, but two years later it was to become reality.”

Despite initial skepticism, the concept was examined in detail by Lieutenant General Frederick E. Morgan and his team at Chief of Staff to the Supreme Allied Commander or COSSAC, who ultimately agreed that a portable, artificial harbour would be essential to any invasion of mainland Europe. However, it was not until the “Rattle” Conference, held in Largs, Scotland, from June 28 to July 2, 1943, that the scheme gained widespread acceptance among Allied planners. But the task would not be easy. The specifications laid out on September 2, 1942 by Lord Louis Mountbatten, Chief of Combined Operations called for a structure the size of Dover Harbour, with piers at least one mile or 1.6 kilometres long to accommodate the 8-metre draft of Liberty Ships, the Allies’ standard mass-produced cargo vessels. The whole system had to be easily transportable, assembled in less than three weeks, last at least 90 days, and be capable of handling up to 12,000 tons of cargo and 2,500 vehicles every day – all while withstanding the 7 metre tides and savage storms of the Normandy Coast. And if all that weren’t enough, everything had to be designed, built, and ready to go in only eight months.

An Artificial Harbours Sub-Committee was duly set up under the chairmanship of civil engineer Colin White, which held its first official meeting on August 4. Meanwhile, a testing station had already been established at Garlieston Harbour on the Solway Firth in southwest Scotland. The site was chosen due to its geographic and hydrographic similarity to the Normandy invasion beaches as well as its remoteness, which would reduce the number of curious onlookers. Small-scale prototypes were also tested at the National Physical Laboratory in Teddington, southwest London, using special tanks fitted with wave-making machines.

Three main concepts were selected for evaluation, codenamed “Hippo”, “Spud”, and “Swiss Roll.” Of these, the “Swiss Roll” was by far the most innovative. The concept was the brainchild of engineer Ronald Hamilton, the type of eccentric but brilliant tinkerer commonly known in Britain as a “boffin.” In February 1942, Canadian chemist Charles Goodeve, head of the British Admiralty’s Directorate of Miscellaneous Weapon Development – AKA the “Wheezers and Dodgers” – received a phone call from physicist and later Nobel Laureate Edward Appleton, who asked him:

“I wonder if you could find time to see a man named Hamilton. He’s an extraordinary fellow … an inventor . . . and he’s got a laboratory fitted up in a bombed wing of the Grosvenor Hotel. He’s working on some ideas which I think might interest you.”

At the hotel, Goodeve discovered that Hamilton had constructed a 200-foot-long water tank using bricks and linoleum, in which he had constructed a model of his floating harbour concept. As he explained to Goodeve:

“I have discovered something which may revolutionize warfare. If certain laws are obeyed the surface of a fluid can be made to behave in many ways like that of a solid. You can lay a sheet of canvas on water and roll a wheeled object over it in just the same way as you could if the canvas was laid on the ground… This theory of mine I call it Rolling Dynamic Buoyancy can solve one of your greatest problems in an amphibious assault. My floating bridge gives you the link between the ships and the shore. Perhaps you’d like to examine this model.”

Hamilton’s invention consisted of a long roll of canvas tarpaulin covered in an assembly of hinged wooden planks and anchored to the seafloor at both ends. When a vehicle drove down the middle of the canvas, the planks on either side were forced upwards, forming a temporary “boat” that supplied just enough buoyancy to support the vehicle in accordance to Archimedes’s principle. And once the vehicle passed a particular spot on the roadway, the planks and tarpaulin fell back to their original flat position. Completely flexible, the entire assembly could be rolled up, ferried to the target by a landing craft, and rolled out up to a mile to connect ship to shore. To demonstrate the feasibility of the concept, Hamilton rolled a toy truck along the model roadway in his testing tank. He also showed Goodeve photographs of his son Peter riding a motorcycle across a larger prototype laid across the stream.

Goodeve, immediately taken in by the concept’s simplicity, took Hamilton onboard as a consulting engineer. Development trials soon began at Portsmouth dockyard, with prototype Swiss Rolls being stretched between a crane barge and the shore. There were many technical difficulties to be overcome: for example, how to unroll the roadway and anchor it against currents and tides under combat conditions, how to prevent vehicles from veering off the roadway, and how to protect it against enemy fire and rough seas – the latter of which were simulated by driving a Motor Torpedo Boat past at high speeds to generate seven-foot waves. Progress was slow and often chaotic, thanks to Hamilton’s manic personality and insistence on making endless refinements to the design. By the time the prototype was demonstrated before senior officers from the Admiralty, the War Office, and Combined Operations on September 25, 1942, relations between Hamilton, Goodeve, and the entire DMWD organization had nearly broken down. Nonetheless, the prototype performed admirably, and in early 1943 construction of a full-scale version began in Cardiff, Wales. Following initial sea trials off Appledore, Kent, the Swiss Roll was sent to Garlieston for competitive trials against other harbour designs.

The second harbour concept selected for testing was “Hippo”, designed by Welsh civil engineer Hugh Iorys Hughes. Hughes had originally submitted his concept to the War Office in 1941, but it did not gain traction until August 1942 after his brother, a Commander in the Royal Navy, intervened. The “Hippo” design comprised a series of floating concrete caissons which could be towed to the invasion beaches and anchored offshore. An articulated metal roadway codenamed “Croc” was then laid atop the caissons to connect ship to shore. Being buoyant, the caissons and attached roadway would rise and fall with the tide. Construction of the prototype Hippos was carried out at Morfa, Wales, by over 1,000 workers under the direction of Oleg Kerensky, son of former Russian Prime Minister Alexander Kerensky, who fled to the UK when his father’s Provisional Government was overthrown by the Bolsheviks in the 1917 October Revolution.

The third harbour design was created by Colonel William Everall and Major Allan Becket of the War Office’s Transportation 5 Department with the assistance of biology professor John D Bernal of Cambridge University. In this design, articulated roadways called “Whales” floated on pontoons called “Beetles”. These were anchored on the seaward end to pier heads called “Spuds”, which could move up and down vertical pilings resting on the seafloor, allowing the whole harbour to rise and fall with the tide.
Official trials at Garlieston, which began in August 1943, quickly revealed serious flaws in the first two designs. When Ronald Hamilton’s flexible Swiss Roll roadway was tested using a three-ton dump truck, it sank in under two hours. And despite numerous refinements, further testing revealed that the system could not support loads of over seven tons, making it unsuited to use with heavier vehicles like tanks. Even lighter vehicles were forced to drive along at low speed in low gear, often causing their engines to overheat. But the final nail in the coffin for Swiss Roll came in September 1943 when a violent storm tore the prototype away from its moorings and washed it out to sea. The innovative concept was consequently abandoned for use in Operation Overlord.

Hugh Hughes’ “Hippo” concept fared little better, for the concrete caissons did not rise and fall with the tide as expected, causing the “Croc” roadways to buckle. Hughes attempted to fix the problem by fitting adjustable spans between the Hippos and Crocs, but the unexpected pitching and yawing of the Hippos introduced massive twisting forces that could not be overcome. Thus, Hughes’s concept was also eliminated from contention, leaving only Bernal and Beckett’s “Spud and Whale” design.

Meanwhile, government officials were growing impatient with the slow pace of the project. On May 30, 1942, Winston Churchill had sent a terse memo to Lord Louis Mountbatten, head of Combined Operations, urging the construction of:

“Piers for use on beaches. They must float up and down with the tide. The anchor problem must be mastered. Let me have the best solution worked out. Don’t argue the matter. The difficulties will argue for themselves.”

A year later, little progress had been made, prompting a frustrated Churchill to write another memo on March 10, 1943 stating:

“This matter is being much neglected. Dilatory experiments with varying types and patterns have resulted in us having nothing. It is now nearly six months since I urged the construction of several miles of pier.”

Much of the delay, it turned out, stemmed from the designers’ attempts to create an artificial harbour that could withstand the full fury of English Channel weather. However, it soon became apparent that this was impossible, and that the harbour would need some sort of breakwater to protect it from rough seas. To drive home the need for such a structure, in September 1943 Professor Bernal arranged an unusual demonstration aboard the ocean liner SS Queen Mary, which was carrying Churchill and his Chiefs of Staff to the Allied summit in Quebec City, Canada. The demonstration took place in one of the liner’s opulent bathrooms – an appropriate venue given Churchill’s well-known penchant for working in the bath. As the onlookers crowded around a large bathtub, First Sea Lord Admiral Sir Dudley Pound stood on a toilet seat and invited them to imagine the shallow end of the tub as the invasion beachhead. Professor Bernal then placed a fleet of 20 small folded-paper boats on the water while Lieutenant Commander D.A. Grant used a back brush to generate waves. As expected, the paper fleet sank. Then, Bernal inflated a “Mae West” lifebelt, placed it on the water, and placed a new fleet of paper boats inside it to simulate a sheltered harbour. This time, no matter how vigorously Lieutenant Commander Grant agitated the waters, the ships were unaffected. Churchill and his Chiefs of Staff were immediately convinced, and at the Quebec Conference advocated vigorously for the concept. Despite continuing skepticism from the Americans, under intense pressure from the British the proposal was ultimately accepted, with official go-ahead being granted on September 4. The entire project was dubbed “Mulberry” – a name with no particular significance which was simply chosen from a list of approved codenames – and to learn more about the importance of keeping codenames as non-descriptive as possible, please check out our previous videos Death by Blue Peacock: Britain’s Bizarre and Deadly Cold War “Rainbow Codes”, and The Forgotten Tech War. The Quebec delegates decided that two harbours would be built: Mulberry A for the American invasion forces and Mulberry B for the British and Canadians – which was later affectionately dubbed “Port Winston”. As the Joint Chiefs of Staff declared in a later memorandum:

“This project is so vital that it might be described as the crux of the whole [Normandy invasion] operation. It must not fail.”

And who said playing in the bathtub was a waste of time?

But what form would the vital breakwaters take? Initially a number of outlandish proposals were floated, including two codenamed “Bubble Breaker” and “Lilo.” The former involved pumping air through a sunken pipe to create a wave-pacifying screen of bubbles, while the latter comprised large hollow canvas booms seven metres in diameter which could be inflated with low-pressure air and anchored to the seafloor. However, Bubble Breaker was ultimately rejected as too complex and impractical and Lilo as too fragile. Instead, the Artificial Harbours Subcommittee selected a system using two nested laters of breakwaters. The outer layer consisted of rigid floating barriers called “Bombardons”, made of steel and rubber and measuring 200 feet long and 25 feet across. These would be towed to the beaches by the tugboats and anchored to the seabed with cables. The next layer was composed of obsolete civilian block ships codenamed “Corncobs”, sunk in rows off the beaches to form breakwaters known as “Gooseberries”. Unfortunately, both the Royal Navy and U.S. Navy were reluctant to sacrifice any usable ships, and were so hostile to Artificial Harbours Committee that Rear Admiral William Tennant, the mastermind of the Gooseberry scheme, quipped that:

“We came here to get a Gooseberry, and all we seem to have got is a raspberry!”

In the end, both Navies released a small fleet of 61 ships, composed mainly of obsolete cargo vessels but also the British dreadnought battleship HMS Centurion, the French dreadnought battleship Courbet, and the Royal Netherlands Navy cruiser HNLMS Sumatra. As a result, the Gooseberries had to be supplemented with hundreds of purpose-built reinforced-concrete caissons codenamed “Phoenixes”, measuring 60 metres long, 20 metres wide, and 20 metres tall and weighing 6,000 tons each. Like the Bombardons, these would be towed across the channel by tugboats before being flooded with water to sink them to the seabed.

Inside these protective breakwaters, the seaward side of the harbours were anchored by “Spud” pier heads, which could rise and fall with the tide along four vertical pilings resting on the seafloor. From these pier heads stretched the articulated “Whale” roadways, which floated on regularly-spaced steel or concrete pontoons called “Beetles.” The whole assembly was firmly fixed to the seabed by cables connected to special anchors codenamed “Kites.”

But even with the design finalized, the challenges were far from over. As Winston Churchill later wrote:

“The whole project was majestic…[involving] the construction in Britain of great masses of special equipment, amounting in aggregate to over a million tons of steel and concrete. This work, undertaken with the highest priority, would impinge heavily on our already hard-pressed engineering and ship-repairing industries. All this equipment would have to be transported by sea to the scene of action, and there erected with the utmost expedition in the face of enemy attack and the vagaries of the weather.”

This assessment was echoed by Major General Sir Harold Wernher, the senior British Army officer in charge of the project, who stated:

“Perhaps the greatest difficulty in getting the project underway after the plan was approved was the vast number of interested parties who had to be consulted or thought they ought to be consulted…[we assembled a team comprising] three of the best brains from the consultant engineers in Britain, and alongside them were placed leading contractors in naval installation together with British and American officers.”

In addition to technical and logistical difficulties, the project was also plagued by infighting between the Admiralty and the War Office, which was only resolved on December 15, 1943 through the intervention of the Vice-Chiefs of Staff. This reorganization gave the War Office responsibility for constructing the Whales, Beetles, Phoenixes and other components of the Mulberry system and defending the harbour with anti-aircraft guns mounted on the Phoenix caissons. Meanwhile, the Navy was tasked with towing these components to the beaches and sinking the Gooseberry blockships in place. Once the components were delivered to the beach, the task of assembling them into functioning harbours would be handed over to other organizations: the U.S. Navy Civil Engineer Corps for Mulberry A and the British Royal Engineers for Mulberry B. Command of the War Office component of the Mulberry project was assigned to Colonel Vassal Steer-Webster and the Navy component to Rear Admiral H. Hickling.

By far the most daunting part of the entire project was the construction of the massive Phoenix breakwater caissons. This task involved 200 civilian construction firms and 200,000 workers working at shipyards and beaches across the UK including London, Tilbury, Woolwich, Barking, Portsmouth, Southampton, Middlesbrough, and Conwy Morfa in North Wales. A total of 212 Phoenixes were built, 147 of which were ready before D-Day. The scale of the construction effort was staggering, absorbing one million tons of concrete and 70,000 tons of steel and costing some £25 million – nearly £1.4 billion in today’s money. Construction was so speedy, in fact, that the builders quickly ran out of space to store the caissons, forcing them to be sunk in shallow water and raised or “resurrected” later – hence the name “Phoenix.”

Construction of the Phoenixes and other Mulberry components was directed by Royal Engineers Brigadier Sir Bruce White, a veteran harbour builder and brother of Artificial Harbours Sub-Committee chairman Colin White. Brigadier White maintained tight security around the whole operation, such that very few of the civilian workers knew what the giant concrete caissons were actually for. Indeed, when a rumour began to circulate that the structures were merely intended for the postwar building trade, a senior Army officer had to be dispatched from Whitehall to reassure the workers that they were, in fact, engaged in vital war work.

But such large structures could not easily be hidden from the enemy, and the Phoenixes were soon spotted and photographed by German reconnaissance aircraft. German intelligence quickly deduced their function, and in May 1944 William Joyce – the Irish-American pro-Nazi broadcaster known to the British as “Lord Haw-Haw” – announced to his listeners that:

“We know what you’re doing with those caissons. You intend to sink them off the coast when the attack takes place. Well, chaps, we’ve decided to help you. We’ll save you trouble and sink the caissons before you arrive.”

But the joke was on the Germans, for Brigadier White had ordered the Phoenixes to be stored in plain sight on beaches and in river estuaries near Dover, right across the Channel from Calais, France. This was but one part of a massive – and ultimately successful – deception campaign known as Operation Bodyguard, designed to fool the Germans into thinking the Allied invasion force would land in Calais instead of Germany – and to learn more about this ingenious undertaking, please check out our previous video The Bizarre Story of the Massive Fake Army That Defeated the Nazis and Helped End WWII.

There were also other, less expected security breaches, such as when multiple D-Day codewords like “Utah”, “Omaha”, “Neptune”, “Overlord” – and, yes, “Mulberry” – began appearing in the crossword puzzles of The Daily Telegraph newspaper – and to learn more about this peculiar incident, please check out our video That Time Crossword Puzzles Almost Gave Away the D-Day Landings over on our sister channel Highlight History.

Meanwhile, the Royal Navy assembled a special team of hydrographers to select appropriate sites for the Mulberry Harbours. Between November 26 1943 and January 31, 1944, the 712th Survey Flotilla, operating from the HMS Tormentor naval base in Hamble-le-Rice, Hampshire, carried out six survey missions on the Normandy coast, using Landing Craft Personnel (Large) or LCP(L)s to take depth soundings and land commandoes to take samples of the beach sand – and to learn more about this humble little vessel and how it changed the face of warfare, please check out our video The Ugly Little Boat That Won WWII over on our sister channel Highlight History. As a result of these surveys, Saint-Laurent-sur-Mer in the American Omaha Beach sector was chosen for Mulberry A and Arromanches in the British Gold Beach sector for Mulberry B.

In spite of some minor mishaps – including one incident where a Phoenix ran aground near Southampton and had to be raised by a specialized salvage crew – all the Mulberry components were completed in time for D-Day: the 6th of June, 1944. The Corncob blockships and tugboats towing the Phoenix caissons actually left their anchorages at Portland, Poole, Plymouth, Selsey, and Dungeness on June 4, but were ordered to halt mid-channel when the invasion was postponed by one day due to weather. At 12:30 on D+1, with the invasion beaches now secure, 45 blockships arrived off the coast and scuttled in their designated positions. In total, 5 Gooseberry breakwaters were installed, one in front of each invasion beach: 10 ships at Utah, 15 at Omaha, 16 at Gold, 9 at Sword, and 11 at Juno. The Bombardon breakwaters and the Phoenix caissons soon followed, while construction of the mile-long piers proceeded round-the-clock under the direction of Captain Reginald Gwyther of the Royal Engineers. The construction did not go unopposed, with the Germans raining long-range artillery fire on the Mulberry sites. And while several shells managed to hit the Phoenix caissons, they were already in position and sank exactly as planned. One month later on July 15, the Luftwaffe carried out an air raid against the harbours. However, by this time most of the caissons had been equipped with defensive guns, which succeeded in shooting down 9 of the 12 attacking aircraft.

The breakwaters proved so effective that the Mulberries started being used before they had even been finished, with cargo ships and landing craft unloading cargo as soon as the Gooseberries were sunk. By June 15, over 15,000 British and 18,000 U.S. troops, 2,000 vehicles, and 25,000 tons of supplies were being landed every day.

But on June 16 the weather began to turn, and towing and assembly operations had to be temporarily halted. On the morning of the 18th the weather appeared fine, and a fleet of tugboats crossed the channel towing four Phoenixes and 23 Whale pier sections. But as the fleet approached the Normandy coast the skies began to darken, and in the early morning hours of June 19th a savage storm descended, with winds blowing up to 30 knots and whipping up eight-foot breakers. It was, as Major Ronald Cowan of the Royal Engineers later wrote:

“…[a storm] such as had not been seen in the Channel for 80 years—second only to the one that smashed the Spanish Armada in 1588.”

One Phoenix and 11 Whales were lost in the storm, while the still-incomplete harbours risked being torn apart. Lieutenant Colonel Raymond Mais, in charge of the piers and pierheads, sprang into action, ordering the “Kite” anchors doubled, ships outside the harbours to keep clear of the breakwaters, and a fleet of over 500 tugboats and landing craft dispatched to help guide wayward ships ashore and keep the fragile harbour together. For four days, Navy and Army crews toiled round-the-clock braving howling winds and giant waves to keep Mulberry B, AKA “Port Winston”, up and running. By the time the storm blew itself out on June 23, 7,000 tons of cargo had been successfully landed. But the weather had taken its toll, destroying or badly damaging six caissons and dozens of pontoons, pier heads, and roadway sections. An official Royal Engineers history described the scene:

“The Allied beaches were a sorry and disheartening sight; hundreds, almost thousands, of craft and small ships—some up to 1,000 tons deadweight—were lying on the beaches at and above the high-water mark in a shambles which had to be seen to be believed; craft were actually piled on top of each other two and three deep.”
Yet despite this, the damage was deemed repairable – a fact largely attributable to Colonel Mais’s quick action and the presence of the Calvados Reef, which had contributed an extra layer of protection from the storm.

But Mulberry A had not been so lucky. Over four days, the storm destroyed two blockships and all the Bombardons and displaced 10 Phoenixes, allowing heavy seas to enter the anchorage and completely wreck the floating piers. So severe was the damage that the decision was made to abandon the harbour.

The storm of June 19-23 1944 severely affected the Allied buildup and breakout from the Normandy beachhead. By the 24th, General Omar Bradleys’ Twelfth United States Army Group had only three days of ammunition left, while Lieutenant General Miles Dempsey’s British Second Army was a full three divisions under strength. With the success of the Allied invasion hanging in the balance, Royal Engineers crews worked day and night to get Port Winston back to full capacity, using parts salvaged from the wrecked Mulberry A. Though only designed to last three months, Port Winston was still in use eight months after D-Day. For while by mid-September Allied forces had succeeded in capturing the port cities of Cherbourg and Le Havre, the Germans had so thoroughly sabotaged the harbour facilities that it took several months to get them up and running again. Meanwhile, though the piers at Mulberry A had been destroyed, landing craft, “rhino” pontoon ferries, and DUKW amphibious trucks were still able to take advantage of the sheltered waters behind the Gooseberry and Phoenix caissons to land supplies directly onto the beaches. By the time Port Winston was finally closed down in early 1945, 2.5 million men, half a million vehicles, and four million tons of supplies had passed through the artificial harbour.

The Mulberry Harbours were an outstanding engineering achievement, unmatched in the history of amphibious warfare, and is widely considered to have been a key factor in the success of Operation Overlord. General Eisenhower later declared that “Mulberry exceeded our best hopes”, while his deputy, Air Chief Marshal Sir Arthur Tedder concluded:

“The whole question of the invasion of Europe might well have turned on the practicability of these artificial harbours.”

Even the Germans, who had devised a similar system for Operation Sea Lion, their abortive invasion of the British Isles, were impressed, with war production minister Albert Speer admitting that: “To construct our defences we had in two years used some 13 million cubic metres of concrete and 1½ million tons of steel. A fortnight after the Normandy Landings, this costly effort was brought to nothing because of an idea of simple genius. As we now know, the invasion force brought their own harbours, and built, at Arromanches and Omaha, on unprotected coast, the necessary landing ramps.”

But not all were convinced of Mulberry’s utility, with U.S. Navy Admiral John Leslie Hall declaring that:

“I think it’s the biggest waste of manpower and equipment that I have ever seen. I can unload a thousand LSTs at a time over the open beaches. Why give me something that anybody who’s ever seen the sea act upon 150-ton concrete blocks at Casablanca knows the first storm will destroy? What’s the use of building them just to have them destroyed and litter up the beaches.”

Indeed, despite losing their Mulberry piers to the June 19 storm, the Americans still managed to land some 180,000 troops, 20,000 vehicles, and 56,200 tons of supplies directly onto Utah and Omaha beaches using ordinary landing craft, calling into question whether the Mulberry harbours were even necessary at all. Nonetheless, the scheme was considered successful enough that Mulberry harbour components and engineers were sent to the Pacific in anticipation of the Allied invasion of Japan. However, the dropping of the atomic bombs and the subsequent Japanese surrender rendered them redundant. Today, little remains of this historic engineering feat aside from a handful of Gooseberry blockships and Phoenix caissons jutting out of the water just off Arromanches. Following the decommissioning of Port Winston, sections of Whale roadway were also used to repair or replace bombed-out bridges as the Allies advanced across Western Europe. Several of these bridges still exist today, including at Les Bordeaux in Normandy and Vacherauville in the Meuse department.

And now for an epilogue of sorts. Despite losing out to Allan Beckett’s “Spud and Whale” concept, Ronald Hamilton continued to refine his “Swiss Roll” concept – and indeed, at least one example was actually deployed at the Normandy Beaches. Its performance, however, left much to be desired. As a contemporary Navy report stated:

“It is perhaps desirable for the sake of completeness to mention as an additional component the Swiss Roll, which consisted of a floating canvas roadway carried on steel wires under tension. But this device was regarded as providing only a stand-by pier and was ultimately used only for landing port personnel and handling Naval stores. Though useful in this way, it was found too fragile and awkward to make any substantial contribution to the harbour facilities and has been described by the Director of Boom Defence (Admiralty) as a stunt.”

Undeterred, Hamilton continued to tinker, developing two designs for floating aircraft runways known as “Lily” and “Clover”. These would allow the Royal Navy to operate aircraft near the invasion beachhead before shore bases could be secured, freeing up regular aircraft carriers for other duties. Lily consisted of two-metre-wide hexagonal flotation chambers which could be towed to the beachhead, bolted together, and covered in steel plating to form a landing surface. Clover, meanwhile, was built of wood and designed to be cheaper and easier to manufacture. Both were extensively tested off the Isle of Arran in the Firth of Clyde, Scotland, using a Taylorcraft Auster and Fairey Swordfish aircraft. While the tests were successful, with both systems proving usable in up to 12-metre waves, the wooden Clover design quickly rotted in marine conditions and was abandoned. Lily was also intended for use in Operation Downfall, the Allied invasion of Japan, but as with the second Mulberry harbour the war ended before it could be used. After the war, Hamilton obtained a Canadian patent for Roads Or Trackways for Supporting Aircraft and Other Vehicles on Water and formed a company, Lilyflex Surfaces, to market it. But before the company could take off Hamilton tragically died in 1953 at the age of only 54, one of countless “Boffins” whose offbeat but often ingenious ideas contributed to much to the ultimate Allied Victory in the Second World War.

Bonus Fact:

Going back to what the D in D-Day stands for…You might at first be inclined to think the abbreviation is similar to V-Day (Victory Day). Indeed, one commonly touted explanation given for the meaning of the “D” in D-Day is that it stands for “designated day.” Others claim it stands for “decision day”, “debarkation”, or even “deliverance day.” Even General Dwight Eisenhower, or at the least his assistant, weighed in when Eisenhower received a letter asking for an explanation of the meaning of D-Day. His executive assistant wrote back stating D-Day was a shortened version of “departed day”.

Given Eisenhower helped plan it, that should mean cased closed right? It turns out, most historians think not. And, indeed, the evidence at hand doesn’t seem to support Eisenhower’s (or perhaps just his assistant’s) claim.

Hints of the true meaning can be found long before WWII in a U.S. Army Field Order dated September 7, 1918. The order stated that “The First Army will attack at H hour on D day with the object of forcing the evacuation of the St. Mihiel Salient.”

In that context, and with numerous combat operations that followed over the years, D-day referred to the “day” on which a combat attack would occur with H-hour likewise referring to the “hour” when an attack is scheduled to happen. Thus, the “D” is just a placeholder or variable for the actual date, and probably originally was meant to stand for “date” or “day” (if anything), if the associated “H-hour” is any indication.

The use of D-day allows military personnel to easily plan for a combat mission ahead of time without knowing the exact date that it will occur. Given that planning for the most famous of all D-day’s in June of 1944 started way back in 1943, and that, due to factors like optimal tides, only a few days in a given month were suitable for the launch of the invasion, trying to fix a firm date in the planning process was pointless, even close to the time of the attack. (In fact, the original set date was June 5, but bad weather at the last minute forced a day delay.) By simply assigning the attack to occur on “D-day”, it solved this issue, and had the side benefit of keeping the date of the attack a secret as long as possible, just one of the many methods of deception the military employed to try to confuse the German brass with regards to the pending invasion.

As for handling the pre-D-day preparations and the plan for after, adding a plus or minus sign and a number after the “D” was used. For example, D-1 would indicate the day before the operation occurring while D+3 would mean three days after the operation. In this way, the plans could be easily overlaid onto a calendar when the military leadership decided on the day of the attack. If the day needed to be switched at the last minute, it was then also easy enough to calibrate the plan to the new date.

As alluded to, the D-Day that occurred on June 6, 1944 was not the only D-day during World War II and it certainly was not the last, as this method of planning for military operations continues to this day. Of course, because the D-day at the Battle of Normandy was, and continues to be, the most famous of all given that designation, it seems unlikely in the foreseeable future that it will be usurped in people’s minds when someone mentions “D-Day”, despite the military continuing to occasionally use this designation.

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