The solution was to build two artificial harbors, code named Mulberries. In June 1943, the British Army Royal Engineers were given the task of designing and building the harbors, each 2 miles long and 1 mile wide. The $100-million cost was staggering then, more so considering that a 1943 dollar was equal to 10 of today's. Normandy has flat beaches with a slope of 1 to 150 and a tidal range of 21 ft. Harbors at invasion sites would have to shelter unloading ships from high waves and provide piers to handle the wide tidal range.

Two days after D-Day, June 6, 1944, a fleet of ancient merchant ships lined up parallel to the shore of Omaha Beach, the main American invasion point, and off Arromanches, the larger of three landing points for British Commonwealth armies. The bottoms were blown out of these ships and they sank in 12 ft of water, forming mile-long breakwaters. A fleet of concrete caissons, each 200 ft long, 60 ft high and 60 ft wide, that were built in Britain were then towed 100 miles to be sunk next to the old ships to enlarge the breakwater. Beyond these were anchored floating breakwaters, steel structures with cruciform cross sections that had one arm extending 6 ft above water.

Within the breakwater-sheltered area, floating piers held in place by spuds could rise and fall with tides. These were linked to shore with half-mile-long floating bridges, also from Britain. Royal Engineers installed the harbor at Arromanches while U. S. Navy Construction Battalions (Seabees) built Omaha's Mulberry (ENR 12/28/44 p. 54).

By June 19, both the U. S. and British Mulberries were in use, although neither was 100% complete. An unexpected fierce storm then hit the Channel. Winds of up to 32 knots piled up huge waves that tore loose the breakwater's sunken ships and caissons and carried away the floating bridges and pier heads. The three-day storm destroyed the American Mulberry. The British Mulberry, sheltered by nearby Calvados Reef, suffered less. Salvaged parts of the U.S. harbor helped repair the British one, which soon reached its 7,000-ton-per-day capacity for the Allies.

Construction Goes to War
(ENR June 29, 1944 p.80)--The U.S. Navy's Construction Battalion, just three years old, was proving itself in World War II's Pacific theater of operations. Galvanized into action by disastrous experiences of civilian construction forces at Wake and Guam, this new arm of military service mobilized more than a quarter-million men and rolled up an enviable record of achievement while building the advanced bases so essential to the success of the U.S. assault. At Guadalcanal, Tarawa and other Pacific sites, Seabees debarked with early waves of combat troops, started construction work while the fighting was in progress and had badly blasted Japanese airfields ready for service a few days after the attack on the bases began and at a time when the areas were still decidedly in the battle zone.

While a Nation Copes at Home
(ENR Feb. 24, 1944 p. 96)--The domestic U.S. construction industry predicted problems in steel availability as the war dragged on, but lumber scarcity was a surprise. The materials paradox was partly due to an increase in need for overseas crating. By the end of 1943, 50% of lumber cut was being used for overseas crating, in contrast to 12.5% normally. In addition, lumber manufacturers were facing a dwindling supply of laborers as workers got called up for military and other service. Production was about 33.5 billion board ft in 1943, but consumption reached as high as 38.5 billion board ft. Federal authorities required design firms to pare down material use.

And New Materials Surface
(ENR Feb. 24, 1944 p. 97)--The lumber shortage and greater steel supplies than expected have triggered more industrial buildings built of reinforced concrete. One such factory complex built for Chrysler Corp. in Chicago includes an 80-acre main building. Precast concrete members, particularly heavy columns, were used extensively. New applications of prestressing were also introduced in building storage tanks for the military. Rods were prestressed in a conventional manner, but the use of a machine to wind wire around the tanks while prestressing it to 150,000 PSI was innovative. In an unusual experiment, an electric current was passed through the wire reinforcing, causing it to lengthen. While held in that position, the reinforcing produced prestresses into the concrete upon cooling.