D-Day

Mulberry Harbours: How The Allies Floated Concrete To Win D-Day

Why were they called Mulberry Harbours and how did concrete make them float…

As much as the success of D-Day was down to the bravery of soldiers, it was made possible by inventions and new machines.

Planning started in 1943 for an attack on five different beaches along an 80km stretch of the Normandy coastline. Utah, Omaha, Gold, Sword and Juno.

The operation depended on the speed with which reinforcements and supplies could reach the frontlines.

The allies knew this all too well and had chosen these beaches with the knowledge that they were going to bring two ports with them.

D-Day Mulberry Harbour Map. Credit to Imperial War Museum
D-Day Mulberry Harbour Map. Credit to Imperial War Museum

All of the parts needed for two huge ports was to be floated across the English Channel whilst the invasion got underway.

Thousands of tonnes was needed to support the battle of Normandy – ammunition, reinforcements, medical supplies, fuel. Each man would need 40kg of supplies per day.

Prime Minister Winston Churchill took a personal interest in the project and made clear that he would accept no delay. He sent a memo in 1942 that was to become famous;

They must float up and down with the tide... don't argue the matter. The difficulties will argue for themselves

The harbor project was given the codename Mulberry. They were to be constructed at Normandy in just two weeks and to have the capacity of the Port of Dover.

Which in 1944 covered 310 Hectares and would discharge 6,000 tonnes of supplies and 1,250 vehicles per day, it’s construction had taken seven years.

To make a floating harbour that ships could come alongside, and carry the weight of tanks and ammunition – the allies would need LOTS of concrete.

In total 275,000 cubic metres of concrete were floated across the channel – a total weight of nearly 600,000 tonnes – and as well as that, 31,000 tonnes of steel.

The construction effort took 45,000 men eight months to complete.

Mulberry Harbour under construction. Credit Imperial War Museum
Mulberry Harbour under construction. Credit Imperial War Museum

By the 6th of June, everything was ready and the harbours were floated across the channel by a team of 132 tugs.

Both harbours were operating from a week after D-Day and when at maximum capacity - a truck or vehicle was being unloaded every minute and sixteen seconds

Mulberry A was constructed off Omaha Beach to supply US forces. Mulberry B – nicknamed Port Winston – was built at Gold Beach at Arromanches to supply British and Canadian troops.

But Mulberry A was destroyed in a storm on the 19th of June.

Port Winston remained fully operational for 6 months after the landings.

Mulberry Harbour Normandy D-Day. Credit US National Archive
Credit US National Archive

For the first two weeks after D-Day, British beaches allowed the unloading of more than 120,000 tonnes, 50,000 vehicles and 285,000 men – all within the shelter of gooseberries. 

After the 20th of June, the harbor itself, mulberry B, was unloading 6,750 tonnes a day.

In total it was used to land over 2.5 million troops, 500,000 vehicles and 4 million tons of supplies.

The use of Mulberry B began to decrease when the allies captured the port of Antwerp.