On D-Day plus one, tugs towing the first components of the artificial ports arrived off the Normandy coast, in front of their two designated sites: Vierville-Saint-Laurent, in the American sector, for Mulberry A, and Arromanches, in the British sector, for Mulberry B.
The principle was the same for both: shelter from the rough seas was provided by a breakwater formed partly by old ships scuttled in situ (Gooseberries), partly by Phoenix caissons. These huge, hollow cubes made from reinforced concrete were carefully positioned, then flooded with seawater, in order to settle them on the seabed. Other caissons were arranged perpendicularly to the shore to form the piers. Once assembled, these components created a roadstead measuring 500 hectares. Further out to sea, external floating breakwaters, or Bombardons, were moored – huge metal structures that had been ballasted and anchored firmly in place.
Ships were unloaded at pierheads that could slide up and down steel stilts according to the height of the tide. The equipment was then transferred to dry land along floating roadways resting on the hollow concrete caissons. Because they were extremely flexible, they could rise and fall with the tide, thereby avoiding any interruptions in unloading operations.
Lorry parks and warehouses were established onshore. Existing roads were widened and new ones laid across the fields to ensure that the huge flow of lorries, guns, tanks, munitions and men reached the front as quickly as possible.
But on June 19th, just as work on the harbours was nearing completion, a violent storm rose in the Channel. It lasted three days and caused extensive damage. The Mulberry at Saint-Laurent suffered the worst. Nearly half its Phoenixes were seriously damaged, many by Bombardons which had been torn from their moorings. The pierheads and floating roadways were swept away. Mulberry B fared slightly better, but still required major repairs. When the storm finally blew itself out, the scene was one of utter devastation. Nearly 800 craft of every sort were stranded on beaches littered with the debris of the floating jetties and other wreckage.
Given the extent of the disaster, the Americans decided not to repair their artificial harbour. Any components that could be recovered were used to repair the British one. The breakwater wall was all that remained, and from then on, craft were unloaded directly onto the beach. Although this may have been a less sophisticated method, it actually turned out to be highly effective, as a far higher tonnage was landed each day at Omaha than at Arromanches.
To say, as some people have, that the Arromanches Mulberry was the key to the success of D-Day may be somewhat of an exaggeration, but it has certainly gone down in history as a brilliant technical feat.