Sketch of one of the Mulberry Harbour pierheads being towed across the Channel, 1944
The Mulberry Harbours were specially designed by the Allies for use after D-Day. Troops could be landed much faster than directly onto the beach. The most important point to the Mulberry Harbours was that the pierheads where the ships unloaded were floating, not resting on the bottom - this meant that they could carry on unloading whether it was high tide or low tide.
This is a drawing showing one of the 'Spud' pierheads being towed over to Normandy, which was to be done after D-Day. The original drawing was done during the planning for D-Day, as part of an illustration of the concept of the Mulberry Harbours. The "DTN" referred to at the top was the British War Office's Department of Transportation.
The 'Spud' pierheads were used by larger ships to unload their cargoes. Each pierhead had four legs, which are the things sticking up into the air. Once in position off the Normandy beaches, the legs rested on the sea bottom at all times, and the horizontal part of the pierhead went up or down on the legs as the tide rose and fell. This meant that the Mulberry Harbours could be used at all times. Normandy had a wide tidal range, meaning that there was great difference between high and low tide. In many normal harbours in areas with a wide tidal range, at low tide the water may be so far below the quayside that ships cannot unload. This was not a problem with the Mulberry Harbours due to their clever design.
Reproduction rights: D-Day Museum, Portsmouth. Do not copy. www.ddaymuseum.co.uk