Waterways tested Mulberries for AlliesPublished 11:08am Friday, June 6, 2014
When World War II broke out, the focus of the U.S. Army Corps of Engineers Waterways Experimental Station in Vicksburg moved from public works projects to meeting the military needs of a country at war.
According to “A History of the Waterways Experimental Station 1929-1979” by Vicksburg historian Gordon Cotton, Waterways engineers and technicians worked on a number of projects that protected coastal and island bases like Midway from erosion by wave action, developing mats to help move equipment off beaches and landing surfaces for aircraft that could be quickly installed and withstand the weight of heavy bombers.
But one project involved testing a British invention that was used in the days after D-Day to provide a continuous train of supplies to Allied troops now fighting on what the German Army called “Ze Normandy Front.”
They were called “Mulberries,” temporary ports installed off the Normandy beaches after D-Day to supply the forces moving inland. One was in the American sector off Omaha Beach, the second in the British sector off Gold Beach.
Sixty old ships were sunk to form five small breakwaters along the French coast. The harbor construction included 150 caissons of six different sizes to suit various depths of water up to 33 feet. The largest displaced 6,044 tons and the smallest 1,627.
The caissons and other equipment were towed across the English Chanel by 85 tugboats and 500 towboats. Only a few were lost to enemy fire as they crossed the choppy water at an average speed of 4 knots (about 5 miles per hour).
A 6-mile flexible steel roadway riding on pontoons made of steel or concrete linked the piers to the shore and allowed trucks to move supplies from ships to supply areas on the shore.
The artificial ports were approved at the Quebec, Canada, conference in the summer of 1943 between English Prime Minister Winston Churchill and President Franklin Roosevelt, but because such a project had never been attempted before, there was no information how the caissons might act in the field, and the task of testing the feasibility fell to Waterways.
The work began in September 1943, using models based on the caisson prototypes.
“The prototypes were 60 feet high by 60 feet wide and 160 feet long,” said Charles Camillo, Engineering Research and Development Center historian. “The engineers at WES built models of them that were five feet long and two feet wide. Each of the models weighed 350 to 360 pounds.”
Engineers used a large wave tank equipped with measuring and recording devices to measure the models’ reactions.
The tank, Camillo said, was tilted to imitate the sea floor along the coast.
“What we did was design a concrete boat,” Fred Brown, who served as project engineer for the artificial harbors, said in a 1984 story about the project published in The Vicksburg Evening Post.
“The idea was to tow the boats, or caissons, across the channel, sink them and create breakwaters,” Brown said. “That would allow the Allies to establish a harbor nearly anywhere.”
To ensure that, the team of Brown, Robert Hudson and Eugene Woodman subjected the models to waves simulating storm conditions that could hit the French Coast, measuring stability, noting the problems and fixing the flaws in the design.
The secrecy of the project worried John B. Tiffany, Jr., who was executive assistant to the director of Waterways in 1944.
“It bothered the hell out of me,” he told the newspaper on the 40th anniversary of D-Day. “I was afraid I might talk in my sleep or it might slip into conversation.”
With the projected late spring, early summer invasion date, time was critical.
“We worked 24 hours a day, seven days a week,” Brown said. “The data was so urgent I’d call Washington every morning to send the information in.”
The final test data were flown directly to England, where the caissons were being built.
The Mulberry components were moved into position immediately after D-Day. Within 12 days after the landings, they were in operation. Although a June 19 Channel storm destroyed the harbor off Omaha Beach, the Mulberry at Gold Beach continued as a port for supplies for 10 months, serving as the embarkation site for 2.5 million men, 500,000 vehicles and 4 million tons of supplies.