Mulberry Harbour Phoenix Caisson, Thorpe Bay, Southend-on-Sea

Back Mulberry Harbour Phoenix Caisson, Thorpe Bay, Southend-on-Sea

One-and-a-half miles off Thorpe Bay, a Phoenix caisson, its back broken, stands on a sandbank. The massive bulk is in two seaweed-encrusted pieces lying end to end orientated NW/SE. The larger of the two is approximately 115 feet (35 m) long; the smaller is 85 feet (26 m) long. The width is around 32 feet (9.75 m)and height up to 20 feet (6 m).

In planning for the invasion of mainland Europe in 1944, it was clear that success would depend not only on the initial capture of beachheads but also on the ability to maintain a constant flow of men and materials into the bridgehead over the following weeks and months. For this, it would be necessary to capture a deepwater harbour. However, all the Channel ports would be heavily fortified against attack and thus to solve this problem the "Mulberry" harbour was conceived - a pre-fabricated harbour built in sections in Britain and towed across to France for assembly off the invasion beaches.

Each harbour - two were eventually constructed - comprised a number of different structural elements. These included Phoenixes, Bombardons and Whales - each designed to fulfil a specific purpose. Phoenixes were huge caissons of concrete up to 200 feet (61 m)  in length, 60 feet (18 m)  high and 50 feet (15 m) wide, which were sunk in position to form the outer breakwater wall. To allow for the reducing depth of water close to the beaches, they were built in a number of different heights. In all, 212 Phoenixes were constructed, many of them at Surrey Docks, Tilbury, Erith and Barking Creek. <1>

One-and-a-half miles off Thorpe Bay, a Phoenix caisson, its back broken, stands on a sandbank. The massive bulk is in two seaweed-encrusted pieces lying end to end orientated NW/SE. The larger of the two is approximately 115 feet (35 m) long; the smaller is 85 feet (26 m) long. The width is around 32 feet (9.75 m)and height up to 20 feet (6 m). The measurements are difficult to confirm as not only are both pieces listing longitudinally but, although on a sandbank, they are surrounded by a "moat" of deep water.

Structurally, the caisson is built of concrete with walls perhaps 12 inches (0.3 m) thick; it is hollow and open to the sky. Internally, cross-members form square cells, two-abreast for the full length of the structure. There are at least 18 cells in all. Pairs of steel bollards appear at intervals along the sides; on top of the larger section a steel tower and light have been erected as a navigational warning to shipping.

November 2000: An article written by Mr. Jim Worsdale and published in the Evening Echo in June 1994 records the provenance of this caisson. The information was provided by Mr. Ian Gordon, a Royal Navy signalman, who was on board the caisson when it was beached. It was being towed from Immingham, on the Humber, to Southsea on the South Coast and en route it sprang a leak. After signalling to HMS Leigh at Southend, it was towed round into the Thames and allowed to sink. 

"Code Name Mulberry" documents the sites around England where each type of Phoenix was constructed. 32-foot (9.75 m) wide caissons, known as Type C1, were built at three locations - Tilbury, Cold Harbour and Goole, on the Humber. Seventeen C1's were constructed from an original program of 147 Phoenix's of all types, although more may have been added when the program was later increased to 212. After completion, this example was apparently towed down river to Immingham where it was subsequently picked up for the voyage southwards, to eventually end its days off Thorpe Bay.  

Close up view of Mulberry Harbour

Close up view of Mulberry Harbour

Detailed view of Mulberry Harbour

Detailed view of Mulberry Harbour

View of Mulberry Harbour

View of Mulberry Harbour

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