Arguably the Normandy landings were the most complex single operation in the history of modern warfare, maybe of any conflict. Spread over five beaches assigned to both the US and British/Canadian Forces, the need for detailed planning was paramount. There was obviously planning for the assembly of troops and the armada of ships, boats and tugs to transport the men and equipment to their destination. Yet this particular activity was fairly late in the planning stages. For example the Duplex Drive tanks used from D-Day onwards were the subject of a US patent which was filed on 13 March 1942 by N. Straussler.
The Beach Groups, a combined British Force comprising all three services, assembled in Scotland in the summer/autumn of 1943, and spent many months on maneuvers. Operation PLUTO ('pipeline under the ocean') started on 14 August 1942, involving engineers, scientists and members of the armed forces working together to design and develop a pipeline capable of being deployed from the Isle of Wight to the Normandy Beaches, pumping fuel to Normandy.
Work on the Mulberry Harbor, the floating temporary harbor erected on two sites supplying British/Canadian soldiers from one beach and the American troops from another, commenced in 1941 at Garlieston, Scotland. Fabrication for the Phoenix caissons (the final chosen construction method) took place along the English South Coast. Some of the Phoenix caissons were abandoned where they were made and are still visible.
Further activities were planned to support the French and create an infrastructure. In one case the Royal Engineers landed a train in case the retreating Germans either destroyed the railway network or immobilized the trains. Additionally an organization, known as Civil Affairs, moved in behind the tanks to set up civil administration. This unit moved slowly through France to Holland."