Phoenix Caisson (inner) off Pagham


Heritage Category:
Scheduled Monument
List Entry Number:
Date first listed:
Location Description:
0.5 miles south-east of Pagham, West Sussex


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The building or site itself may lie within the boundary of more than one authority.

Location Description:
0.5 miles south-east of Pagham, West Sussex
National Grid Reference:


A steel reinforced concrete feature known locally as the Inner Mulberry and commonly believed to be a Phoenix caisson has recently been shown to be an Intermediate Pierhead Pontoon, designed to allow multiple pier heads to be connected together so that more than one ship could be accommodated within the overall Mulberry Harbour units.

Reasons for Designation

The pontoon is scheduled for the following principal reasons:

* Period: the feature is acknowledged as comprising a material record and an eloquent witness to the preparations around England’s coast for the largest amphibious invasion ever undertaken, on 6 June 1944; * Potential: the asset forms a primary source of evidence relating to the ingenuity of the wartime Allies in creating, and building, artificial harbours for use in Normandy, though its form and function is not yet fully understood; * Rarity: as the only confirmed surviving Intermediate Pierhead Pontoon anywhere in the UK.


In June 1944 the Allies opened a Second Front in Europe with Operation Neptune, comprising a largely amphibious invasion on the Normandy coast. In order to supply the armies once they had landed, harbours were necessary to allow supply ships to unload. In the expectation that captured harbours would have been rendered unusable by the enemy, the Allies intended to build two artificial harbours; one in the US sector and one in the British sector. These harbours were code-named Mulberries A and B respectively and Operation Neptune is still considered one of the greatest and most challenging logistical operations of all time.

The Mulberries consisted of four major component structures, code-named Gooseberry (a line of sunken blockships), Bombardon (floating breakwaters), Phoenix (sunken breakwaters) and Whale (pierheads) though designers initially struggled to develop a suitable floating roadway which linked the offshore pierheads with the beach.

The roadway would be required to accommodate lateral as well as vertical movement in each span as the tide rose and fell which led to the development of innovative telescopic bridge spans. In addition, spud pontoons, when operated singly, could not berth more than one ship at a time. A proposal was therefore made for several spud pontoons to be linked by intermediate pontoons attached to one spud pontoon and a telescopic bridge span linking the free end of the intermediate pontoon and the next spud pontoon.

The intermediate pontoons had flared sides and sloping swim-ends to make them easier to tow across the Channel to Normandy and each unit was divided into 18 compartments of which three were reserved for stores and one for living accommodation. It is not yet clear how the pontoon came to be located in the shallow waters off Pagham, but it is located in an area commonly known by divers as the ‘Park’ which contains an exceptional number of submerged (i.e. parked) Second World War sites that are associated with Mulberry harbour operations.


As the intermediate pontoons provided a space for the unloading of stores, the decks had to be strong enough to carry heavy lorries and owing to the shortage of steel in wartime Britain, the pontoon was made using ferro-concrete, a technique pioneered by Messrs Wates at the Vickers Barrow-in-Furness shipyard, and were constructed by civil engineering contractors around the coast of Britain. The vulnerable sides of the pontoons were protected by birchwood fenders. Only twenty-four Intermediate Pierhead Pontoons were built and the unit off Pagham comprises the only known Intermediate Pierhead Pontoon in UK waters.

The pontoon had an unladen draught of 6ft (1.8m) and is 80ft (24.4m) long by 57ft (17.4m) wide. Constructed of steel reinforced concrete, the steel reinforcement is subject to saltwater corrosion although the rate of this corrosion is not known.

However, the site has been visited by divers of Southsea Sub-Aqua Club who took the opportunity to walk around the exposed top of the wreck and noted that the structure ‘is still fairly intact though it is possible to swim through from one side to the other in a couple of places’. The Pontoon is noted for being ‘an excellent dive for novices’ but that ‘the wreck can become overcrowded on sunny summer Saturdays, with strings of divers weaving in and out’.


Books and journals
Hartcup, G (author), Code Name Mulberry. The Planning, Building & Operation of the Normandy Harbours, (2006), 87-9
McDonald, K, A Diver Guide, Dive Sussex, (2003), 60
Raymond , CyrilWood, James, 'Reinforced-Concrete Pier Pontoons and Intermediate Pierhead Pontoons' in n/a,, The civil engineer in war: A symposium of papers on war-time engineering problems, (1948)
Designing and Building the Mulberry Harbour, accessed 08/12/2017 from
Southsea Sub-Aqua Club, 2015, Mulberry 70, Unpublished Project Report
Wessex Archaeology, 2017, Mulberry Units Pagham Harbour, West Sussex, Unpublished Desk-based Assessment


This monument is scheduled under the Ancient Monuments and Archaeological Areas Act 1979 as amended as it appears to the Secretary of State to be of national importance. This entry is a copy, the original is held by the Department for Digital, Culture, Media and Sport.

End of official listing

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