D-Day: Southampton's role in building Mulberry Harbours

In opting for Normandy as the invasion site, the Allies found themselves confronted with specific requirements dictated by the region's geographical features. The absence of substantial harbour infrastructure, with the exception of the nearby fortresses of Le Havre and Cherbourg, presented significant challenges that had to be addressed.

Following the catastrophic events at Dieppe, doubts arose about the feasibility of seizing a port. Military leaders acknowledged that extensive bombing to weaken enemy defences would inadvertently damage vital dock structures, hindering any potential reinforcement efforts.

So as one senior officer put it: "All I can say is if we can't capture a port we must take one with us." The germ of the idea that would turn into Mulberry Harbours had taken root.

In the midst of the Quebec Conference of 1943, with the presence of Roosevelt and Churchill, a consensus was reached regarding the establishment of dual ports, intended to serve the British and American forces, as proposed during the discussions.

With the task at hand looming large, it was imperative that by May 1, 1944, an extensive network of harbours larger than Southampton docks had to be constructed before the invasion force landed on the Normandy beaches.

In just three weeks following the initial landing, the Mulberries needed to be ready to handle anything up to 12,000 tons of stores and 2,500 vehicles a day.

In order to accommodate Liberty ships with a 26-foot draught and also offer protected waters for smaller vessels like landing craft, the docking facilities needed to be spacious and versatile.

Upon finishing the project, all the parts needed to be transported almost 100 miles across the Channel and put together amidst the likely threat of enemy attacks.

Above all else in this innovative and evolutionary strategy, it was imperative that every step of the process remained shrouded in secrecy from start to finish.

As one report on the Mulberry operation notes: "Although sites as far apart as Southampton and Leith, North Wales and Oban were used, no-one gave the secret away.'

The blueprint for the Mulberry project entailed constructing a breakwater using submerged ships and building an outer sea wall of huge concrete boxes, known as Phoenixes. These massive structures were truly enormous, with the heaviest one exceeding 6,000 tons and standing at a towering height of 60 feet.

In an effort to enhance the security provided by the Phoenixes, a series of structures called Bombardons were constructed.

The concept of Bombardons traced back to an unconventional test conducted by engineer Robert Lochner at a trout lake. Lochner improvised by folding a rubber mattress in half and weighing it down with disused gas pipes.

Initially, Bombardon prototypes were crafted using canvas air-bags, but it quickly became apparent that they needed to be more robust to withstand the challenging Channel environment. The decision was made to construct 93 concrete structures, each measuring 200 feet in length and partially filled with water.

Numerous vessels were crafted at the dry docks located in Southampton and Portsmouth, with smaller ones also being assembled at Stokes Bay, Gosport, and Beaulieu. The production involved more than 200 designs fashioned from more than one million tons of concrete and 70,000 tons of steel.

Established at Arromanches and off Omaha Beach, the harbours were nearing completion before encountering a major setback on June 19. Severe Force 8 gales struck the area, unleashing the fiercest storm witnessed along the Normandy coast in four decades.

After the disastrous incident, the once sturdy Omaha Mulberry lay in ruins. Twenty-one of the 28 Phoenix caissons were completely destroyed, the Bombardons were cast adrift, and the roadways and piers smashed.

The Mulberry at Arromanches was damaged but remained intact. It came to be known as Port Winston and saw heavy use for eight months, despite being designed to last only three months. In the 10 months after D-Day, it was used to land over 2.5 million men, 500,000 vehicles, and 4 million tons of supplies providing much-needed reinforcements in France.

With its impressive 600,000 tons of concrete spread across 33 jetties and 10 miles of floating roadways, Port Winston stands out as a remarkable feat of military engineering.

Even today, the remains of this structure can be observed from the shores of Arromanches, serving as a lasting testament to its historical significance.