Transporting a huge invasion force to Normandy, and successfully landing it in the face of determined opposition, posed difficult and diverse problems; no less difficult was the task of keeping the troops supplied once they were established ashore. Since it was perilous, if not actually impossible, to mount a head-on attack against one of the heavily defended ports, such as Cherbourg, the Allies built artificial harbours that could be towed in sections to the landing points and assembled there.
This top-secret project, codenamed 'Mulberry', was approved at the Quebec conference in August 1943, and completion was called for by 1 May 1944. In just seven months, 20,000 workers in construction firms throughout Britain succeeded in producing two enormous prefabricated ports, each as big as Dover Harbour, which could be towed to the French coast. In charge of assembling and placing the Mulberry harbours was Rear-Admiral W.G. Tennant, who, in 1940, had masterminded the evacuation at Dunkirk.
On D-Day + I, the first 45 of 70 old ships were sunk at Arromanches off the British beaches, and at St Laurent off the American beaches, to form breakwaters; then the sections of the harbours were floated into position. The British harbour made an enormous contribution to the success of the campaign, but the American harbour at St Laurent was so badly damaged on 19 June by the worst storm in the Channel for 80 years that it was never completed.
More than two million tons of steel and concrete were towed to the French coast to build the Mulberry harbours. Concrete caissons some 18m/60ft high and weighing 6,000 tons-formed the outer walls of the harbours. Inside, hydraulically operated piers, which rose and fell with the tide, were connected to land by floating roadways. The British Mulberry, [
Below] handled 12,000 tons of cargo and 2,500 vehicles a day.