The wreck in Thorpe Bay – the Mulberry Harbours of the D-Day landings.

About one mile out in the Thorpe Bay is a structure that sticks out of the water, like two triangles. As a always wondered what this was and what was it doing out there. Was it a shipwreck?

Well not quite. The structure is called a caisson and it was one of many which would build up and become Mulberry Harbour (as it is now known) and is a Scheduled Monument. A Mulberry was a portable temporary developed by the British in World War II to facilitate of cargo onto the beaches during the Allied invasion of Normandy. They were part of Operation Overlord and Winston Churchill said that they were ‘a principle part of the great plan’.

What is in the estuary is classed as a with the code name of Phoenix. Its role would be to form an outer sea wall for the temporary in Normandy. It would also, once in place, form a breakwater for the many vessels that would come into port and provide a calm sea. To get it into place the would be tugged across the channel and once at their intended on board would make sure it was aligned right and then sunk 33 feet. Although ours would never even make it out of the channel.

There would be 146 Phoenixes all 60 meters long and 18 meters high. In addition, there would also be Bombardons – floating breakwaters, Gooseberries – obsolete merchant vessels whose role to be filled with explosives and sunk in their final location as a against the enemy.

The whole concept and scale of the two would stretch the capacity of the UK’s civil engineering industry. From the summer of 1943, there were at least 300 firms across the country involved that in turn employed around 40,000 people to complete the task. It was not just those from the engineering trade either, due to a shortage of were given crash courses to assist with the project. In total 212 caissons were to be completed with 23 pier heads and 10 miles of floating roadway.

The structures themselves were only meant to last for 100 days and were just built to do their purpose and nothing more. However, along with the one at Shoeburyness another three survive in British waters with 30 of the caissons in the Arromanches wall in Normandy.

There would be two built for the D-day landings. The first was assembled at Arromanches, which was to support the British and Canadian forces, and the second was Omaha to support the American troops. The first was quite successful in doing its job however; the one Omaha was wrecked during a storm within two weeks of being completed.

The one in the Thames estuary on the West Knock sandbank weighs about 2,500 tones. It was originally built in Immingham the River Humber. It was around 2 June when our was being towed that it sprung a leak and was towed into the estuary to see if repairs could be It was moved to try to keep the shipping lanes got stuck across a sandbank unable to move. Part of the caisson hung over the edge of the bank and eventually the section broke it split into two and stuck in the mud, which is where it still, remains today. One of the parts is about 115 feet long and the smaller 85. They are 32 feet in width and up to 20 feet in height

It is a rare surviving example of its kind. “It reflects an extraordinary engineering project designed to facilitate perhaps the most significant event of World War II – the D-Day counter- invasion and liberation of Continental Europe – and it remains a high visible symbol of this critical point in the history of the war.” (Historic England)


Summers, A and Debenhams J (2008) Essex hundred histories. : Southend-on-Sea

Anon (2004) World War II caisson. Available from: [accessed 10/03/2019]

Anon () Cassion (Phoenix) Breakwater Available from: [Accessed 10/3/2019]

Anon () Mulberry . Available from: [Accessed 11/03/2019]

Skinner, N () Mulberry. Available from: Accessed 10/03/2019]

Tags: thames wrecksmulberry harbourpheonixd-day landingssouthend historysouthend at watsouthend heritagecassions

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