Aerial view of a section of the “Mulberry” artificial harbour at Arromanches, June 1944.
Source: Australian War Memorial – public domain (Accession No. P05052.008).
A feat of maritime engineering
In the spring of 1944, Allied forces undertook one of the most ambitious maritime engineering projects of the 20th century: the construction of artificial harbours along the Normandy coast to support the landings and keep the troops supplied.
Among the key structural components of these harbours were large reinforced concrete caissons, known as Phoenix caissons
Build on land, install at sea
These structures were:
- built on land, mainly in the United Kingdom;
- towed individually across the English Channel;
- sunk and positioned on site;
- arranged in sequence to form an artificial breakwater.
Each caisson rested on its own weight and on its bearing surface on the seabed.
The assembly work was carried out directly at sea, under demanding technical conditions.
The alignment of these elements helped attenuate wave energy and create a sheltered area.
A landmark in maritime engineering
The artificial harbour at Arromanches — Mulberry B — demonstrated that it was possible to:
- industrialise the construction of heavy maritime structures;
- organise their transport on a large scale;
- coordinate their installation at sea under real operating conditions.
This exceptional achievement, carried out under British direction, remains a major reference in modern maritime engineering.
The remains still visible today off Arromanches are a reminder of this ability to design and rapidly deploy heavy offshore infrastructure.
Heritage and technical continuity
Although the contexts differ, certain principles remain highly relevant today:
- land-based prefabrication;
- logistical efficiency;
- control of critical offshore operations;
- understanding of hydrodynamic constraints.
The Phoenix caissons are not a blueprint to be replicated, but a striking example of how engineering can adapt to maritime constraints.
They now form part of Normandy’s maritime and historical heritage.