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Mulberry harbours were temporary portable harbours developed by the United Kingdom during the Second World War to facilitate the rapid offloading of cargo onto beaches during the Allied invasion of Normandy in June 1944. After the Allies successfully held beachheads following D-Day, two prefabricated harbours were taken in sections across the English Channel from the UK with the invading army and assembled off Omaha Beach (Mulberry "A") and Gold Beach (Mulberry "B").

The Mulberry harbours 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. The Mulberry B harbour at Gold Beach was used for 10 months after D-Day, and over 2.5 million men, 500,000 vehicles, and 4 million tons of supplies were landed before it was fully decommissioned. The still only partially-completed Mulberry A harbour at Omaha Beach was damaged on 19 June by a violent storm that suddenly arrived from the north-east. After three days the storm finally abated and damage was found to be so severe that the harbour had to be abandoned.

Design and development

Aerial view of Mulberry harbour "B" at Arromanches (October 27, 1944)
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.[6] 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.[7] Between 17 June and 6 August 1942, Hugh Iorys Hughes submitted a design concept for artificial harbours to the War Office.[8]

At a meeting following the Dieppe Raid of 19 August 1942, Vice-Admiral John Hughes-Hallett (the naval commander for the Dieppe Raid) 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 one mile (1.6 km) 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 (Chairman), 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.[9]

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 (a civil engineer) who developed his "Hippo" piers and "Crocodile" bridge spans;
Ronald Hamilton (working at the Department of Miscellaneous Weapons Development) 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 (of the War Office's 'Transportation 5 Department' (Tn5)) who designed a floating bridge linked to a pier head (the latter had integral 'spud' legs that were raised and lowered with the tide).
The western side of Wigtown Bay, in the Solway Firth, was selected for the trials as the tides were similar to those on the expected invasion beaches in Normandy, a harbour was available at Garlieston, and the area's remoteness would simplify security matters. A headquarters camp was erected at Cairn Head, about 5 miles (8.0 km) south of Garlieston. Prototypes of each of the designs were built and transported to the area for testing by Royal Engineers, based at Cairn Head and in Garlieston.[10] The tests revealed various problems (the "Swiss Roll" would only take a maximum of a 7-ton truck in the Atlantic swell). However the final choice of design was determined by a storm during which the "Hippos" were undermined causing the "Crocodile" bridge spans to fail and the Swiss Roll was washed away. Tn5's design proved the most successful and Beckett's floating roadway (subsequently codenamed 'Whale') survived undamaged; the design was adopted and 16 km (10 mi) of Whale roadway were manufactured under the management of J. D. Bernal and Brigadier Bruce White, the Director of Ports and Inland Water Transport at the War Office.