The D-Day Invasion At Normandy May Not Have Succeeded Without The Mulberry Harbors

The D-Day Invasion At Normandy May Not Have Succeeded Without The Mulberry Harbors

The Mulberry artificial harbors proved a logistical wonder along the beaches of Normandy.

“It Must Not Fail”

The proposal was outlined in Quebec before Churchill, President Franklin D. Roosevelt, and the Joint Chiefs of Staff. The British pressed the idea, and the Joint Chiefs eventually agreed to the construction of two such harbors—“Mulberry A” for the American landing forces and “Mulberry B” for the British and Canadians. The latter harbor was nicknamed “Port Winston.” In a memorandum, the Joint Chiefs wrote, “This project is so vital that it might be described as the crux of the whole [Normandy invasion] operation. It must not fail.”

The specifications were formidable. By D-Day plus 21 days, the two harbors were to be capable of shifting 12,000 tons of cargo and 2,500 vehicles a day. They would have to cope with the full 26-foot draft of Liberty ships and provide a shelter for landing craft in foul weather. Furthermore, each harbor had to have a minimum life of 90 days in order to funnel ashore as much manpower and matériel as possible before the Allied armies could secure a port. The artificial harbors were to be ready by May 1, 1944. The mammoth undertaking was to be completed in a mere eight months.

The Gooseberries were the brainchild of Rear Admiral William Tennant, who from January 1943 onward was in command of the planning, preparation, towing, and placement of the Mulberry harbors. He had a stormy relationship with the Admiralty, which was reluctant to release any usable ships to be sunk as blockships to protect the artificial harbors. Tennant determined that he needed 60 old merchant vessels and warships. At one stage, his deputy said of their lordships at the Admiralty, “We came here to get a Gooseberry, and all we seem to have got is a raspberry!” Admiral Tennant eventually got his 60 blockships. Among them were the 1911 French battleship Courbet and a Dutch cruiser. Assembled in Scotland and loaded with explosive charges, the blockships were to be sunk off the Normandy beaches.

Building the Mulberries strained the administrative capabilities of the senior British Army officer, Maj. Gen. Sir Harold Wernher, who reported, “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.” A team was assembled 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.” At first, the team was in almost continuous session trying to solve the critical problem of designing the outer breakwater.

The largest type of Phoenix caisson that the contractors eventually designed was 200 feet long, 60 feet high, and weighed more than 6,000 tons. More than 213 of all types were built, which required more than a million tons of reinforced concrete and 70,000 tons of steel reinforcement. The piers, code-named bombardons, were attached to massive steel pylons that rested on the seabed. In accordance with Churchill’s directive, the piers did indeed “float up and down with the tide”—assisted by an ingenious system of hydraulic jacks. Linking the piers to the land were the floating roadways made up of steel pontoon bridges (the Whales). The floating roadways and Mulberry anchor systems were designed by Lieutenant Allan Beckett of the Royal Engineers.

200,000 Workers and Eight Months

Dozens of construction companies and 200,000 workers toiled at London, Tilbury, Woolwich, Barking, Portsmouth, Southampton, Middlesbrough, and other ports all over England to complete the artificial harbors in time for D-Day. In all, the two Mulberries required about two million tons of concrete and prefabricated steel. There were about 623,000 tons of reinforced concrete in 147 caissons. Huge excavations were carved out in the banks of the Thames and Medway Rivers to allow the great Phoenix units to be built, and 200 tugboats were deployed to haul the harbor parts to their moorings. The whole project was estimated to cost 25 million pounds for the eight-month period.

Led by Sir Bruce White, a World War I Army veteran and former harbor builder, the Royal Engineers supervised the construction phases, while the Royal Navy took care of planning, delivery, and assembly operations. Various segments of the Mulberry structures were stockpiled in streams and inlets around the English coast before their assembly, some within range of German long-range guns at Calais, France. This was a deliberate deception to confuse the enemy about the planned invasion route.

The great project went ahead under tight security. The harbors were built in sections ready for towing to the French coast. One of the Mulberries was to be set up off Omaha Beach at St. Laurent-sur-Mer in the U.S. V Corps landing area, and Port Winston was to be assembled at Arromanches in the British-Canadian-Free French sector of the Normandy beaches. Although the concept appeared simple, the execution was complex and required the skills of many engineers to put the harbors in place. That the entire project took only eight months to complete was signal testimony to the capacity of British industry, already stretched to the limit by four years of war.

Lord Haw Haw’s Broadcast

Secrecy was so stringent that many of the Mulberry component builders did not know what they were working on. When a rumor circulated in the assembly yards that the concrete monoliths were in some way merely destined for the postwar building trade, a senior British officer was sent from Whitehall to reassure the workers that they were in fact doing vital war work. German intelligence did not know what was happening in the southern English ports, although it was certain that the concrete structures must be floating moorings or fuel storage tanks for use in the coming invasion.

Lord Haw Haw (William Joyce), the sardonic-voiced, Brooklyn-born German broadcaster, confidently told British listeners in May 1944, “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.”

A week before the day of the long-awaited invasion, the blockships were scheduled to sail from Scotland to rendezvous with the rest of the Mulberry components. The invasion would be dependent on the successful functioning of the harbors, but until there was the chance to test one in action, none of the planners, engineers, or builders knew just what their capabilities were. That test would not happen until the Mulberries were actually positioned on the other side of the English Channel.

A fortunate accident to one of the Mulberry units averted what might have been a major disaster for the Allies at Normandy. One of the hulking concrete Phoenixes went aground at the Brambles near the southern English port of Southampton. Engineers started to pump it out in order to refloat it, but discovered that they could not raise it because the pumps were not strong enough. A salvage expert was found, along with additional heavy-duty pumps.

Marshaling sufficient tugs powerful enough to pull the giant caissons against the Channel currents proved a major headache for the Royal Navy, but eventually 150 boats were found to be suitable for the crossing and were moved from sites at Portland, Poole, Plymouth, Selsey, and Dungeness. The tugs were distinguished by a large “M” on their funnels, and their crews took great pride in the designation. The British tugs were to be assisted by U.S. Army towing launches.

The Mulberry Harbors on D-Day

Finally, D-Day arrived, and early on the gray, chill morning of Tuesday, June 6, 1944, British, American, Canadian, and Free French assault troops waded ashore on Gold, Juno, Sword, Utah, and Omaha Beaches at Normandy. The Mulberry harbors and associated Gooseberries were ready to play their part in the massive, meticulously planned Allied crusade. Each harbor, built of two million tons of steel and concrete, enclosed an area the size of Dover, two square miles.

The first convoy of 45 blockships arrived in the assault area at 12:30 pm on June 7, and the sinking of the vessels was started at once. The rest of the Mulberry harbor sections followed in a round-the-clock effort. Convoys of eight Phoenixes, eight bombardons, four pierheads, 10 Whale roadways, and two miscellaneous units were towed across the choppy Channel by the tug fleet. The planned speed of three and a half knots was increased to four and a half to reduce the turnaround time. Losses of 20 to 25 percent were expected on the crossing, but few units sank, apart from half of a floating roadway. The Mulberries were in use even before they were fully assembled. Almost from the moment that the first Gooseberries settled into the sand, ships were unloading behind them, protected from the Channel waves.

Great skill was required in assembling the two harbors on the Normandy coast. A key blockship had first to be sunk precisely in position. The initial attempt to do this at Mulberry B failed; the tugs at the stern of the first ship, the Alynbank, let go early. As she was settling down more slowly than planned, the tide turned and swung the Alynbank at right angles to the required position. But this turned out for the best because she formed a useful shelter from the west. At Mulberry A, the positioning of blockships went ahead at a faster pace. At the end of the first week, it was decided to plant an extra Phoenix there. But this was undertaken in failing light and falling tide, and the result was a large unit positioned too close to the main harbor entrance.