The biggest amphibious operation in WWII, Operation Overlord, began with the landing of the Western Allies on the beaches of Normandy on June 6th, 1944. Allied soldiers managed to hang onto the shore and push the Germans back from La Manche with more than just shells and bullets. Engineering vehicles worked no less than infantry, tanks, and ships. Bulldozers, assault bridges, mine flails, and fascines laid the road for soldiers from the narrow strip of sand further inland. Underwater pipelines and enormous floating harbours provided fuel, ammunition, and medicine for the Allies.
Let us look at engineering solutions in the Normandy operation.
Transports, bulldozers, bridgelayers, and other vehicles must reach the beach along with infantry. Without them, making it through obstructions, wire, and minefields on the shore would have been much more difficult.
Bulldozers went into action soon after the landings started. There were various types, regular bulldozers with armour plates welded on and tank bulldozers. Americans used regular M4 Sherman tanks equipped with bulldozer blades and hydraulic devices for raising and lowering them. The tank remained combat-capable. At the time of the landing, the US Army had about a hundred of these engineering hybrids. The British had about 250 "Centaur" bulldozers, built on a Cromwell chassis with the turret removed.
There was plenty of work to be done. The bulldozers destroyed obstructions on shore, moved away damaged landing craft and other vehicles, cleared the roads, covered up bomb craters, and cleared minefields. Sometimes they even dealt with enemy bunkers, burying them. During low tide, bulldozers worked on more convenient landing zones for subsequent waves of soldiers.
During the failed landing at Dieppe in 1942, walls by the shore became a serious obstacle for tanks. The British took that into account and created the Churchill ARC MkI. The tank's turret was removed and replaced with two ramps, the rear one longer than the front. The tank was supposed to climb as far up as possible on the walls and then open the ramps, allowing other vehicles to drive over the obstacle.
There was another widely used vehicle on the Churchill chassis, the AVRE engineering tank. Some of them were armed with a supercaliber (the diameter of the shell is greater than the diameter of the barrel) 290 mm spigot mortar, firing 18 kilogram HE shells to destroy fortifications. Others were equipped with mine flails, explosive charges, assault bridges, and various other sapper equipment. The crew of the AVRE was interesting: only one man was a tanker, the rest were engineers.
"The longest day" finished with a success, but the main part of the offensive was yet to come.
By the end of the first day, 150,000 men and hundreds of tanks and other vehicles were on shore. This was far from the entire force destined for Overlord, the total was many times higher. In order to deliver the people and vehicles, as well as supply them with everything necessary, British engineers built two unique constructions: Mulberry artificial harbours.
These massive structures consisted of a whole system of seawalls, piers, and roads. The construction of the harbours was carried out in secrecy since 1943. In total, they were composed of over 200 enormous concrete pontoons and 70 obsolete ships that were loaded with ballast and turned into foundations. Mulberry piers could rest on either these ships or their own foundations that could be raised during transport and lowered at the destination.
Why were these harbours necessary? The experience of the aforementioned Dieppe raid showed that significant casualties are unavoidable when taking a well defended port, and these piers allowed the British to avoid these casualties. Setting up the piers only took a few days. Building a regular harbour takes years, even at peace time.
On June 6th, the tugboats towing the foundation ships came under heavy fire. Fortunately, the Germans managed to sink a few ships where they were supposed to sink. A protective barrier calmed the waters in the harbour, and on the next day, tugboats delivered the multi-ton pontoons, each with a crew of two sailors and two AA gunners. They were positioned next to Omaha and Gold beaches, about a mile from shore. Each harbour was about a mile long, and towered 3-9 meters above the sea, depending on the tide.
The first harbour, Mulberry A, was unlucky. On July 19th, the strongest storm over the past 40 years hit La Manche and destroyed most of its pontoons. The remainder were used to repair Mulberry B. Thanks to these two harbours, over two million men, half a million vehicles and four million tons of cargo were delivered on shore. This was an engineering wonder of the 20th century. According to Dwight Eisenhower, the construction of these harbours was the most daring element of the landings.
Underwater Veins of Overlord
Operation Overlord needed a steady stream of fuel. A hidden network of fuel pipes was laid from Bristol and Liverpool to La Manche. The pump stations and terminals were disguised as garagers, quarries, or even ice cream shops. But how can the fuel get over the channel?
The British developed a plan of building an underwater pipeline called PLUTO (PipeLine Under The Ocean) with the help of engineers from the Britain-Iraq Oil Company. The basis was the well tested technology of underwater pipelaying, aside from the core. This was an incredibly reliable technological process. Some telephone cables laid this way in the 19th century kept working until the 1950s.
There were two types of pipes planned: lead and steel. The lead one used a 5 cm thick pipe covered in several layers of thin steel strips reinforced with steel wire. Trials in 1942 showed that the pipeline needed significant internal pressure, or it would be crushed or burst. Engineers came up with a clever design. The lead pipe was covered with paper saturated with bitumen, steel wire, and jute. The steel design was almost the same (except for a greater diameter, 7.5 cm) and was developed because lead was in deficit at wartime. External pressure was as dangerous for these pipes as internal, which is why they were filled with water during laying, so that they were not crushed by their own weight.
The pipelines were wound on enormous spools, unrolled with steam-powered winches. One spool weighed more than two destroyer ships at the time. Over 30 ships participated in the laying. The first proper pipeline was finished on August 12th, 1944. Work only took less than 10 hours, even though the pipeline was over 130 km long. The amount of pipelines constantly increased. By spring of 1945, nearly 20 steel and lead veins connected Britain to the mainland. By the end of the war, they pumped about 700 million tons of fuel.
The success of the Western Front was built on a firm foundation. Soldiers and commanders could be sure that new tanks, cars, and reinforcements will be there on time and their fuel won't run dry at the most inopportune moment.
Original article available here.