Mulberry harbours

The ingenious solution was to build an artificial harbour, called 'Mulberry'. Huge concrete blocks, called 'Phoenix', were towed across the Channel and then sunk in place by flooding them. These acted as a breakwater to ensure calm conditions inside the 'harbour'. Inside the artificial harbour created by Phoenix were floating docks on to which the vehicles were lifted. They were then driven to the beachhead on a flexible floating steel roadway. Within six days, an astonishing 330,000 men and 54,000 vehicles had been brought ashore. Within a month there were a million men in France facing just 400,000 German troops. Fuel was provided by PLUTO (Pipeline Under The Ocean), laid after D-Day.

Neil Demarco: The era of the Second World War; Oxford University Press, 1993/2000, page 45