World War II Day by Day

 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, Scot­land, and North­ern Ire­land by up­wards of 200,000 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/­0.8 km 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 2 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 British pounds in 1944 (worth well over $1.4 bil­lion in 2024). Built of rein­forced concrete, the floating harbor piers, or landing wharves (code­named “Spuds”), were con­nected to the inva­sion beaches by a string of 80‑ft/­24‑m-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/­6.4 m twice a day.

Besides ppiers 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 6 of these mon­sters in all) was 200 ft/­61 m long, 60 ft/­18 m high, and weighed in excess of 6,000 tons. More than 213 “Phoenix” cais­sons of all types of 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 “Goose­berries” (sunken ships) 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/­8‑km-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

Left: Forming a 2‑mile/­3.2‑km-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 6 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 3 Normandy assault beaches.

Right: Seven floating pier heads or landing wharves (Spuds) were con­nected by bridges. Each wharf could simul­ta­neously berth 2 amphib­ious ves­sels such as LSTs (Landing Ships, Tank) or LCVPs (Landing Crafts, Vehi­cle, Per­son­nel, commonly known as Higgins boats) or one 26‑ft/­8‑m draft, 7,198‑ton Liberty ship with its heavy and bulky cargo. Looking like chim­neys, 4 square towers pierced each corner of the 7 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.

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 2 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.

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/­5.2 km. 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 4 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/­24‑m pontoon-mounted bridge spans (Whales) totaling 3,000 ft/­914 m 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 2 bridges in Cameroon.

Right: Wrecked Mulberry “A” floating roadway, the result of a huge 3‑day gale, the worst in 40 years, on June 19–22, 1944. The gale broke the backs of 2 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 2 shel­tered harbors than the storm itself. On June 23, after the gale had blown itself out, Lt. Gen. Omar N. Brad­ley, com­man­der of U.S. First 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