London, England September 4, 1943

On this date in 1943 the British War Office and Admiralty gave the go-ahead to build two temp­o­rary port­able deep-water arti­fi­cial har­bors, one (code­named Mul­berry “A”) to be posi­tioned off Omaha Beach at Saint-Laurent-sur-Mer and the second (Mulberry “B”) off Gold Beach at Arro­manches-les-Bains. The com­po­nents of both har­bors were to be pre­fab­ricated in England, Wales, and Scot­land by up­wards of 200,000 British laborers inside 8 months. Then every­thing was to be towed by more than 100 tugs across the treach­er­ous English Chan­nel to their desti­na­tions a half mile off the French Nor­mandy coast, the site of D‑Day, the in­va­sion of German-occupied North­western Europe. Oper­a­tion Over­lord, the code­name for the up­coming Allied liber­a­tion of Normandy and ulti­mately the whole of France and Western Europe, was sorely in need of a harbor or two for off­loading assault troops, mili­tary equip­ment, precious ancil­lary matériel (e.g., fuel, ammu­ni­tion, food, and medi­cine), and rein­force­ments that would sus­tain the inva­sion’s momen­tum. The ill-fated Anglo-Cana­dian Dieppe Raid (Oper­a­tion Jubi­lee) the pre­vious August demon­strated to the Allies that liber­a­ting the conti­nent by attempting to seize a defended French port (Dieppe, Cher­bourg, Le Havre, Dunkirk, or Calais) was at best a fool’s errand.

The building of these two mammoth secret weapons—Mulberry Harbor “A” and “B”—was a tech­ni­cal and logis­ti­cal marvel at the time. It came at a mind-blowing cost: 25 mil­lion pounds (worth well over 1.1 bil­lion in today’s pounds). Built of rein­forced concrete, the floating harbor piers, or landing wharves (code­named “Spuds”), were con­nected to the inva­sion beaches by a string of 80‑foot-long floating bridges (“Whales”) weighing 56 tons each that were attached to floating pon­toons (“Beetles”). These con­crete-and-steel struc­tures were designed to adjust to Normandy’s tides that rose and fell 21 ft twice a day.

Besides piers and roadways, the harbors required breakwaters. Break­waters com­prised floating break­waters (“Bom­bardons”), next to which huge, hollow con­crete cais­sons (“Phoe­nixes”) were deposited on the sea floor. The largest type of Phoenix cais­son (there were six in all) was 200 ft long, 60 ft high, and weighed in excess of 6,000 tons. More than 213 of all types were built. The final harbor require­ment was a series of dere­lict ves­sels, or block­ships (“Corn­cobs”), that could steam or be towed across the Chan­nel to be scuttled stem to stern, there­by adding a third ring of pro­tec­tion against high waves and meddle­some currents. Gaps in the line of these 70 sunken ships (“Goose­berries”) allowed supply ships to enter and exit the protected anchorage.

On the afternoon of D‑Day, June 6, 1944, over 400 towed com­po­nent parts (weighing approx­i­mately 1.5 mil­lion tons) set forth to create the cargo-handling har­bors. They in­cluded the block­ships to create the outer break­water and the Phoe­nix cais­sons. At Arro­manches the first Phoe­nix was sunk at dawn on June 8, 1944. By June 15 a further 115 had been sunk to create a five-mile-long pro­tec­tive arc off Gold Beach. The first Phoe­nix off Omaha Beach was sunk on June 9 and the Goose­berry breakwater was finished on June 11.

Both harbors were almost fully functional when on June 19 a large north­east storm at Force 6 to 8 blew into Normandy and devas­tated the Mul­berry harbor at Omaha Beach. The Mul­berries had been designed with summer weather con­di­tions in mind, but this was the worst storm to hit the Normandy coast in 40 years. The destruc­tion at Omaha was so severe that the entire harbor was deemed irre­pa­ra­ble. Twenty-one of the 28 Phoenix caissons were totally destroyed. The harbor at Arro­manches was more pro­tected, and although damaged by the storm it remained in­tact. It came to be known as Port Win­ston after British Prime Minis­ter Win­ston Chur­chill. Port Win­ston saw heavy use for 8 months, despite being designed to last only 3 months. In the 10 months after D‑Day, it was used to land over 2.5 mil­lion men, 500,000 vehi­cles, and 4 mil­lion tons of sup­plies, pro­viding much needed men and matériel to France as Allied armies sprinted east toward the German border. The cap­tured Bel­gian port of Antwerp in Sep­tember eliminated the need to maintain Port Winston.

Operation Overlord’s Secret Weapon: Mulberry Artificial Harbors

Mulberry Artificial Harbor: Building Mulberry "B" breakwater, Gold Beach, June 12, 1944Mulberry Artificial Harbor: Mulberry "A"’s "Spuds" line up at Omaha Beach, June 1944

Left: Forming a two-mile-long breakwater at Arro­manches, part of Mul­berry “B” harbor at Gold Beach, is a line of rein­forced con­crete Phoenix cais­sons (with dis­place­ments of approx­i­mately 2,000 tons to 6,000 tons each) being moved into posi­tion by tugs on June 12, 1944. Sea­cocks were opened to allow water to sink the hollow cais­sons—each as much as six stories tall and as long as a city block—into posi­tion. Anti­air­craft guns were mounted on the largest cais­sons and bar­rage bal­loons floated over­head as pro­tec­tion against enemy air­craft. The Phoe­nixes formed the Mul­berry harbor break­waters together with the Goose­berries (scuttled or block ships), whose super­struc­tures remained above sea level. Goose­berries were also placed off the other three Normandy assault beaches.

Right: Seven floating pier heads or landing wharves (Spuds) were con­nected by bridges. Each wharf could simul­ta­neously berth two amphib­ious ves­sels such as LSTs (Landing Ships, Tank) or LCVPs (Landing Crafts, Vehi­cle, Per­son­nel, commonly known as Higgins boats) or one 26‑foot draft, 7,198‑ton Liberty ship with its heavy and bulky cargo. Looking like chim­neys, four square towers pierced each corner of the seven floating wharves to anchor the struc­tures to the sea­bed. Unfor­tu­nately, the U.S. Navy Civil Engi­neer Corps did not securely anchor Mul­berry “A” to the ocean floor as did their British counter­parts, the Corps of Royal Engi­neers, at Arro­manches (Mul­berry “B”). During the violent Chan­nel storms of late June 1944 Mul­berry “A” incurred damage so severe that it was con­sidered irre­par­able and further assem­bly ceased. Though the Omaha harbor was aban­doned in late June, the sandy beach itself con­tinued to be used for dis­em­barking troops, vehi­cles, and stores and eva­cu­a­ting the wounded uti­lizing LSTs and simi­lar craft. Using this method, the Amer­i­cans were able to un­load a higher ton­nage of cargo than the British at Arro­manches. Salvage­able parts of the Omaha arti­fi­cial harbor were sent to Arromanches to repair the Mulberry there.

Mulberry Artificial Harbor: Army truck traverses Mulberry "A"’s "Whale" floating roadwayMulberry Artificial Harbor: Black American soldiers construct landing ramp at Mulberry "A"

Left: A U.S. Army truck traverses a Whale floating road­way leading from a Spud pier at Mulberry “A” off Omaha Beach. The British Admiralty’s Depart­ment of Miscel­laneous Wea­pons Develop­ment played an instru­mental role in devel­oping parts of the two arti­ficial Mul­berry har­bors used in the D‑Day landings. By June 9, 1944, just 3 days after D‑Day, Mul­berry “A” and “B” har­bors were under con­struc­tion at Omaha and Gold beaches, the Amer­ican and British invasion beaches, respectively. Within the first 2 weeks of D‑Day, 20 fighting divi­sions and more than a million men were ashore.

Right: Black American soldiers construct a landing ramp at the end of a Whale floating road­way as part of Mulberry “A” at Omaha Beach. The ramp was steel mesh laid over wooden staves.

Mulberry Artificial Harbor: Drill instructor Sgt. Gilbert (Hashmark) JohnsonMulberry Artificial Harbor: Wrecked Mulberry “A” floating roadway

Left: An aerial view of Mulberry “B” harbor. Built of 2 million tons of steel and concrete, each Mul­berry enclosed an area the size of England’s Dover harbor, or 2 sq. miles. Once in­side the Mul­berry’s break­waters (lower right in photo), ships and barges would anchor at a Spud pier head to dis­charge their cargoes. Pier heads were held on the sea­bed by four steel legs. The stout legs were built so that the piers could be raised and lowered in rela­tion to the tide with the assis­tance of hydraul­ic jacks. The piers were directly con­nected to the shore by artic­u­lating 80‑ft pontoon-mounted bridge spans (Whales) totaling 3,000 ft in length as shown in the left half of the photo. After the war many of Arro­manches’ bridge spans were used to repair bombed bridges in France, Bel­gium, and the Nether­lands. Some spans were used to build two bridges in Cameroon.

Right: Wrecked Mulberry “A” floating roadway, the result of a huge three-day gale, the worst in 40 years, on June 19–22, 1944. The gale broke the backs of two Goose­berry block­ships. The floating outer break­waters (Bom­bar­dons), though moored to the sea­bed, had been tied together by hemp rope. Some of the Bom­bar­dons broke up and sank while others broke free of their infe­rior moorings to col­lide with the block­ships, con­crete cais­sons, and floating piers and road­ways, possi­bly causing more damage to the two shel­tered harbors than the storm itself. On June 23, after the gale had blown itself out, Lt. Gen. Omar N. Brad­ley, com­man­der of First U.S. Army at Utah and Omaha beaches, strolled the beachfront, wincing at the damage: “I was appalled by the deso­la­tion, for it vastly exceeded that on D‑Day.”

Mulberry Artificial Harbors: D-Day’s Temporary Floating Harbors

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