For a Closer Look
ENR Dec. 28, 1944 p. 53
ENR Dec. 28, 1944 p. 55

With German forces having heavily fortified the French coast and every French port by the middle of 1944 during World War II, the Allies faced the difficult problem of how to unload all the troops, weapons, ammunition, fuel and other supplies on the Normandy beachheads. British naval strategists conceived of building two massive artificial harbors, code named Mulberry, one at Saint Laurent sur Mer (Omaha Beach) for the American forces and the other at Arromanches (Gold Beach) to support British and Canadian forces, as they carried out the largest seaborne invasion in history.

Engineered Approach

The elaborate system included fixed breakwaters of two types, floating breakwaters and piers with floating pierheads. Each Mulberry featured a 6,500-ft-long breakwater running parallel to the shore, 4,500 ft offshore, composed of open concrete caissons “phoenixes”—200 ft long, 60 ft wide and 60 ft high, each weighing up to 6,000 tons. A second set of phoenixes 1,600 ft long was set at a right angle leading towards the beach for additional protection from wave action. Each phoenix hosted a 40-mm antiaircraft gun. Thirty nine phoenixes were installed at each harbor. They were constructed in secrecy by 19 British construction firms at dry docks and tidal basins along Britain’s south coast.

Flanking the phoenix breakwater was an additional 6,500-ft-long breakwater called “Gooseberry,” comprised of 14 older merchant ships and one outmoded battleship, towed into position and sunk using explosives. Their superstructures protruded from the water and their antiaircraft guns were manned, aiding in defense. Parallel to the shore and 3,000 ft further out than the phoenix breakwater was a floating breakwater made up of 24 steel units, cruciform-shaped in cross section, extending 6 ft above the surface, to break up the wave action.

Inside the protected anchorage formed by the inner breakwater were three parallel piers extending 3,200 ft from shore, composed of 100-ft-long steel truss sections supported by moored concrete or steel pontoons. Each pier carried a 10-ft-wide steel deck roadway. The piers connected to pierheads known as Loebnitz piers, floating steel platforms steadied by spuds, where landing craft could unload vehicles and cargo. The spuds were not intended to support the pierheads’ entire weight but to carry enough load to anchor and steady it; an arrangement of pulleys and cables and power winches raised and lowered the pierhead as the tide flooded and ebbed. The Loebnitz piers were chosen from among four competing prototypes tested at Wigtown Bay in Scotland, chosen because the tides there were similar to those at Normandy.

The complete construction sequence for the harbors was to be 18 days following June 6, 1944, D-Day. Most of the phoenixes were towed across the English Channel, positioned, and sunk within the first week. U.S. Navy Construction Battalions—Seabees—manned the phoenixes, pierheads and pier sections while they were in tow across the English Channel and handled their installation.

At the same time, three dozen jury-rigged “Rhino ferries”—clusters of barges lashed together and fitted with pontoons and outboard engines—conveyed 300-ton loads to the shore. Each Rhino was up to 42 ft by 176 ft, able to carry 30 or 40 vehicles.

For the first two weeks following D-Day the effort went well, but nature had other plans. A gale-force storm from June 19-22 wrecked the Omaha Beach installation beyond repair. The Mulberry complex at Gold Beach suffered less damage, as it was situated in shallower water and protected by a rocky shoal.

Despite the damage at Omaha Beach, between the intact Mulberry harbor at Gold Beach and the Rhino ferries working at capacity, the supply effort succeeded. Rhinos alone shuttled 16,000 vehicles ashore at Omaha during the first ten days. Over its ten months of its service, the Mulberry at Gold Beach funneled over two million soldiers, four million tons of supplies and half a million vehicles onto French soil.

Details of these artificial harbors were subject to strict military censorship, which was lifted in October 1944. ENR published a brief article that month, followed by a comprehensive eight-page account in the December 28, 1944 issue.