Mulberry harbours
The Mulberry harbours were two temporary portable harbours developed by the British Admiralty and War Office during the Second World War to facilitate the rapid offloading of cargo onto beaches during the Allied invasion of Normandy in June 1944. They were designed in 1942 then built in under a year in great secrecy; within hours of the Allies creating beachheads after D-Day, sections of the two prefabricated harbours were towed across the English Channel from southern England and placed in position off Omaha Beach and Gold Beach, along with old ships to be sunk as breakwaters.
The Mulberry harbours solved the problem of needing deepwater jetties and a harbour to provide the invasion force with the necessary reinforcements and supplies, and were to be used until major French ports could be captured and brought back into use after repair of the inevitable sabotage by German defenders. Comprising floating but sinkable breakwaters, floating pontoons, piers and floating roadways, this innovative and technically difficult system was being used for the first time.
The Mulberry B harbour at Gold Beach was used for ten months after D-Day, while over two million men, four million tons of supplies and half a million vehicles were landed before it was fully decommissioned. The partially completed Mulberry A harbour at Omaha Beach was damaged on 19 June by a violent storm that arrived from the northeast before the pontoons were securely anchored. After three days the storm finally abated and damage was found to be so severe that the harbour was abandoned and the Americans resorted to landing men and material over the open beaches.
Background
The Dieppe Raid of 1942 had shown that the Allies could not rely on being able to penetrate the Atlantic Wall to capture a port on the north French coast. The problem was that large ocean-going ships of the type needed to transport heavy and bulky cargoes and stores needed sufficient depth of water under their keels, together with dockside cranes, to offload their cargo. These were only available at the already heavily defended French harbours. Thus, the Mulberries were created to provide the port facilities necessary to offload the thousands of men and vehicles and millions of tons of supplies necessary to sustain Operation Overlord. The harbours were made up of all the elements one would expect of any harbour: breakwater, piers and roadways.Preparation
With the planning of Operation Overlord at an advanced stage by the summer of 1943, it was accepted that the proposed artificial harbours would need to be prefabricated in Britain and then towed across the English Channel.The need for two separate artificial harbours – one American and one British/Canadian – was agreed at the Quebec Conference in August 1943. An Artificial Harbours Sub-Committee was set up under the Chairmanship of the civil engineer Colin R. White, brother of Sir Bruce White, to advise on the location of the harbours and the form of the breakwater; the Sub-Committee's first meeting was held at the Institution of Civil Engineers on 4 August 1943. The minutes of the Sub-Committee's meetings show that initially it was envisaged that bubble breakwaters would be used, then blockships were proposed, and finally, because not enough block ships were available, a mix of blockships and purpose-made concrete caisson units were used.
On 2 September 1943 the Combined Chiefs of Staff estimated that the artificial ports would need to handle 12,000 tons per day, exclusive of motor transport, and in all weathers. On 4 September the go-ahead was given to start work immediately on the harbours. Infighting between the War Office and the Admiralty over responsibility was only resolved on 15 December 1943 by the intervention of the Vice-Chiefs of Staff. The decision was that the Admiralty managed the blockships, bombardons and assembly of all constituent parts on the south coast of England. It would also undertake all necessary work to survey, site, tow and mark navigation. The War Office was given the task of constructing the concrete caissons, the roadways and protection via anti-aircraft installations. Once at the site, the army was responsible for sinking the caissons and assembling all the various other units of the harbours. For the Mulberry A at Omaha Beach, the US Navy Civil Engineer Corps would construct the harbour from prefabricated parts.
The proposed harbours called for many huge caissons of various sorts to build breakwaters and piers and connecting structures to provide the roadways. The caissons were built at a number of locations, mainly existing ship building facilities or large beaches, like Conwy Morfa, around the British coast.
Beach surveys
Both locations for the temporary harbours required detailed information concerning geology, hydrography and sea conditions. To collect this data a special team of hydrographers was created in October 1943. The 712th Survey Flotilla, operating from naval base HMS Tormentor in Hamble, were detailed to collect soundings off the enemy coast. Between November 1943 and January 1944 this team used a number of specially adapted Landing Craft Personnel, or LCP, to survey the Normandy coast.The LCPs were manned by a Royal Navy crew and a small group of hydrographers. The first sortie, Operation KJF, occurred on the night of 26/27 November 1943 when three LCPs took measurements off the port of Arromanches, the location for Mulberry B. A follow-up mission, Operation KJG, to the proposed location for Mulberry A happened over 1 and 2 December but a navigation failure meant the team sounded an area 2,250 yards west of the correct area.
Two attempts to take soundings were made off Pointe de Ver. The first sortie, Operation Bellpush Able, on 25/26 December had problems with their equipment. They returned on 28/29 December, in Operation Bellpush Baker, to complete the task.
The final Mulberry harbour survey, Operation Bellpush Charlie, occurred on the night of 30–31 January but limited information was gathered due to fog and because German lookouts heard the craft. Further sorties were abandoned.
Design and development
An early idea for temporary harbours was sketched by Winston Churchill in a 1915 memo to Lloyd George. This memo was for artificial harbours to be created off the German islands of Borkum and Sylt. No further investigation was made and the memo was filed away.In 1940 the civil engineer Guy Maunsell wrote to the War Office with a proposal for an artificial harbour, but the idea was not at first adopted.
Churchill issued his memo "Piers for use on beaches" on 30 May 1942, apparently in some frustration at the lack of progress being made on finding a solution to the temporary harbour problem. Between 17 June and 6 August 1942, Hugh Iorys Hughes submitted a design concept for artificial harbours to the War Office.
At a meeting following the Dieppe Raid of 19 August 1942, Vice-Admiral John Hughes-Hallett declared that if a port could not be captured, then one should be taken across the Channel. Hughes-Hallett had the support of Churchill. The concept of Mulberry harbours began to take shape when Hughes-Hallett moved to be Naval Chief of Staff to the Overlord planners.
In the autumn of 1942, the Chief of Combined Operations Vice-Admiral Lord Louis Mountbatten, outlined the requirement for piers at least long at which a continuous stream of supplies could be handled, including a pier head capable of handling 2,000-ton ships.
In July 1943 a committee of eminent civil engineers consisting of Colin R White, J D C Couper, J A Cochrane, R D Gwyther and Lt. Col. Ivor Bell was established to advise on how a number of selected sites on the French coastline could be converted into sheltered harbours. The committee initially investigated the use of compressed air breakwaters before eventually deciding on blockships and caissons.
Churchill discussed the Mulberry harbour idea with President Roosevelt. The Secretary of Labor, Frances Perkins, recorded Roosevelt’s comments, “You know that was Churchill’s idea. He has a hundred a day and about four of them are good”
Trials
In August and September 1943 a trial of three competing designs for the cargo-handling jetties was set up together with a test of a compressed air breakwater. The pier designs were by:- Hugh Iorys Hughes who developed his "Hippo" piers and "Crocodile" bridge spans;
- Ronald Hamilton who devised the "Swiss roll" which consisted of a floating roadway made of waterproofed canvas stiffened with slats and tensioned by cables;
- Lieutenant Colonel William T Everall and Major Allan Beckett who designed a floating bridge linked to a pier head.