Mulberry Harbour

With plans for the Allied invasion of Normandy (also know officially as Operation Overlord and unofficially as the D Day landings) the allies needed deep water harbours to allow unloading of troops and cargo. Previous attempts to take control of French ports, for example Dieppe, showed them to be heavily defended and experience in the Mediterranean had shown that the Germans would destroy port facilities rendering them unusable. Smaller ports such as Cherbourg were inadequate for the quantities of cargo.

It became clear that the initially everything would need to be unloaded at open beaches until the ports could be restored. However this would be vulnerable to bad weather and the underside of the landing vehicles could be damaged by continuous landing on the beaches.  This resulted in a plan for an offshore portable harbour with a breakwater to protect the ships from storms and roadways for landing vehicles. The day after Churchill issued his famous memo ‘Piers for use on beaches’ on 30 May 1942, a member of the Office of the Chief of Staff wrote to Iorys Hughes requesting he prepared proposals on the Prime Ministers orders for landing piers to be towed across the Channel.

Letter from the Office of the Chiefs of Staffs to Iorys Hughes, 1 June 1942 [ICE Archive ICE 1863/1/01]

hippo and phoenix

Hughes produced designs for the prototype concrete caisson piers, which he called Hippos. His design was later modified and became to the concrete Phoenix units

Iorys Hughes’s designs for the Hippo [ICE Archive ICE 1863/1/01]

The units were built at Conwy and tested at Rigg Bay on the west coast of Scotland as the coast was similar to the Normandy beaches.


Hughes also designed Crocodile roadways or ‘Crocs’ to link the units whilst Colonel William T Everall and Major Allan Beckett also designed a floating bridge which linked to a pier head. The pier heads could be raised and lowered using spud legs to allow them to adjust with the tide. The designs were tested in August and September 1943 when Everall and Beckett’s roadway proved more successful under storm conditions.

Iorys Hughes’s designs for the Crocodile roadways [ICE Archive ICE 1863/1/01]

The components for the harbour went into production with most of the country’s major civil engineering companies involved.  Due to the secrecy of the project the components were divided amongst the companies so no-one knew what they were building.

List of companies supplied with concrete units by Cyril Parry of Muswell Hill, June 20 1944. Given the date it seems that these would be for Phoenix Units. [ICE Archive ICE 1963/08/01]

An Artificial Harbours Sub-Committee was set up to advise on the breakwater and the location of the harbour. They held their first meeting at ICE on 4th August 1943.  The Minutes of the meeting are available online at The sub-committee considered using bubble breakwaters whereby compressed air is released under water to create bubbles to reduce the waves.  They decided on blockships (sunken scuttled ships) but with not enough available, the breakwater was created by a combination of blockships and Phoenix units.

The harbour included 10 miles of floating bridge, 6 miles of concrete caissons and 23 bridge heads and covered an area compatible with Dover harbour.

Over 45,000 people worked on components for the harbour. The work was top secret and most workmen did not know what they were building.

The harbours were assembled off Omaha Beach (Mulberry “A” for USA) and Gold Beach (Mulberry “B” for UK), but Mulberry A was damaged by a storm before it was completed and could not be used.

Mulberry B was used for 10 months after D Day and was used to land 2.5 million men, 500,000 vehicles and 4 million tons of supplies.