In the lead-up to D-Day the UK Government began construction on a Top Secret Project that would enable the allied invasion to literally take a harbour with them.
The Project was The Mulberry Harbour, a floating concrete harbour built in sections and towed across the English Channel to the beaches where the initial invasion took place. The need of such a vast undertaking was because all the ports were very heavily fortified by the Nazi forces and to aid the advance through occupied France the allies needed to get large amounts of men, machines and supplies to the front line.
The Southend Phoenix Caisson was originally built in Immingham on the banks of the River Humber; the section was in the process of being towed to Southsea, Hampshire in preparation for the D-Day landings when it began to let in water.
The caisson was diverted by the admiralty into the Thames Estuary so that the leak could be investigated and repaired.
Upon entering the Thames, it fell under control of HMS Leigh at Southend Pier, the radio operator directed the towing vessel to keep the main shipping lanes clear so it was decided to position the Caisson over the West Knock sandbank.
Once it was in position the taps that flooded the structure were opened to allow the gradual controlled sinking to take place.
However the caisson shifted position as the flooding process was taking place. This resulted in the caisson settling on the sandbank with three-quarters supported and the rest hanging over the edge of the bank.
The stresses exerted on the unsupported section proved too great and the back of the section broke rendering it useless to the war effort.
The hulk has been left where it settled to this day, it lays 1.2miles off the shore at Thorpe Bay and is clearly visible at all states of tide.
It is NOT advised to attempt to walk out to the Mulberry as the tides come in very fast at right angles to the beach, there is a high risk of getting cut off from shore as the foreshore is covered in channels and sand banks do not risk death!.