A digital reconstruction of the D-Day landings harbour and vehicles demonstrates the ingenuity of yesterday’s engineers and the capabilities of today’s technology.
How modern engineering can bring wartime innovation to life
World War Two spawned a huge number of innovations, many of which were documented in the pages of The Engineer (though others remained a closely guarded secret for years). As part of the upcoming 70th anniversary celebrations of D-Day, a number of those innovations have been recreated in digital form.
French software firm Dassault Systemes is attempting to build a virtual, 3D reconstruction of the Normandy Landings, complete with fully accurate representations of some of the aircraft, boats and physical structures that were created for it.
Among those is one of the most impressive pieces of temporary engineering you could envision: the Mulberry harbours. One of the reasons the Nazis didn’t expect the Allies to invade via Normandy was the difficulty of landing and unloading hundreds of thousands of troops and their equipment on such flat beaches.
To get around the challenge of capturing an existing port, Churchill and his advisers came up with the idea of bringing one across the Channel and erecting it on the beaches. Multiple breakwaters, pontoons and floating roadways were all towed over in thousands of pieces after the initial landing force and assembled in the shallow but exposed waters of the Normandy Coast.
The Americans completed theirs in three days. The British and Canadians took seven. But when, two weeks later, a storm ravaged the coast, it was the British harbour – known as Mulberry B – that remained intact and became the main landing point for the rest of the invasion.
The harbour, which was equivalent to the size of that at Dover, included a number of innovations. The pierheads at which ships would unload rested on so-called “spud legs”, were originally developed by the Scottish shipbuilding firm Lobnitz for dredgers.
These legs comprised tubes with a central pile that could be pushed into the seabed, allowing the pontoon to float freely on the legs but also to winch itself up when necessary to withstand the load of unloading ships – making it one of the first ever jack-up pontoons.
Although not designed to do so, the pierheads were actually able to lift themselves completely out of the water during the storm, saving them from the destruction of the wave.
Another innovation was the creation by engineer Allan Beckett of the floating roadways that led from the pierheads to the short. Each comprised a series of pontoons, codenamed “beetles”, connected by an 80-foot steel bridge, codenamed a “whale”, that could support a 40-tonne tank.
Because of wartime shortages, only those beetles that came to rest on the seabed at low tide were made of steel. Those that permanently floated were made using hollow concrete structures made from panels and stitched together in-situ.
Because knowledge of the precise geography of the rocky beach was limited, the steel pontoons had legs that could be individually adjusted against the uneven seabed to level the structure.
The whale roadways were actually designed to operate without breakwaters, which Mulberry had in the form of numerous sunken ships and concrete cassions placed on the sea bed at the perimeter of the harbor to reduce the impact of the waves.
Each section of whale comprised two lozenge-shaped girders connected by a central plate and pinned so they could twist independently. The sections were held together with system of spherical bearings that enabled them to move without locked-in stresses.
To recreate the harbour, Dassault’s team sourced the original blueprints - 30 tubes’ worth of them. But while they were able to easily reconstruct the individual pieces, they had no instructions for putting them together. For this they turned to photos, eyewitness accounts and, importantly, Allan Beckett’s son Tim, himself a civil engineer and port designer.
They had more trouble with the other two elements of the project so far completed: the Waco glider used to carry men and vehicles behind enemy lines and the shallow-hull LCVP troop-landing boat. Both craft had been built of wood (and fabric in the case if the Waco) and none had survived from the time of the landings.
Months of searching turned up plans of varying quality but, to improve the accuracy of their models, the team also found restored versions of huge two craft in museums and user a laser scanner to create ‘point cloud’ digital images of them. This enabled them the designers to build 3D computer models that represented every aspect of the craft accurately right down to each individual screw and nut.
The project has given Dassault an opportunity to both test and show off its software capabilities, and also to demonstrate how such reconstructions displayed with the latest 3D projection technology can help bring history to life.