The Wellington DWI was one of the most distinctive aircraft variants to serve during the Second World War. It was developed in response to the German use of magnetic mines in the early weeks of the Second World War. Dropped from Luftwaffe aircraft in British coastal waters, these magnetic mines sank an increasing amount of ships in the early part of the war.
The key breakthrough was the retrieval of an intact mine. With this to examine two solutions to the problem were developed. One was to degauss the ships, thus removing their magnetic field. This would allow the degaussed ships to pass safely over the magnetic mines, but would leave the mines themselves intact.
A second solution was to deliberately generate a magnetic field that would detonate the mine. Attempts to do this from a ship succeeded in detonating the mines, but also damaged the ship.
The successful solution the problem involved attaching an aluminium coil inside a balsa wood ring with a diameter of 51 feet, attached to a Wellington IA bomber. This gave the bomber a very distinctive appearance. Power was provided by a Ford V8 engine driving an electrical generator. When the power was fed into the coil it generated a magnetic field that could trigger the magnetic mine.
Tests on land proved that the basic concept was correct. However, sweeping an area for mines was not a simple matter of flying low over the sea. The aircraft had to fly slow and low enough to trigger the mine, but not so slow or low that it would be damaged by the explosion. This was a very low level operation – initial tests took place at 60 feet, with 35 feet felt to be the minimum safe altitude.
The DWI equipment achieved its first successful detonation of a mine on 8 January 1940, without a problem. The second detonation, on 13 January, was rather more dramatic – the Wellington had drifted below the safe 35 feet altitude and was thrown into the air by the explosion. Once again, the Wellington’s robust geodetic construction proved its worth, and the aircraft suffered no damage.
Only a small number of DWI Wellingtons were produced. The two original prototypes were joined by the DWI Mk II, which used a lighter but more powerful Gypsy Six motor to generate the power. The Wellington DWI aircraft needed a fighter escort, as all of their guns had been removed, although none were actually attacked in British waters. The system was also used in the Mediterranean, with one Wellington DWI Mk I reaching Egypt in May 1940, with more aircraft converted to perform the role in the field.
The DWI equipped Wellington was an early example of what Churchill called the “Battle of the Boffins” – the endless scientific war that saw first one side then the other win a brief technological advantage, before eventually the shear weight of allied resources gave them an almost unassailable lead later in the war. Along with the development of simple degaussing methods, the DWI Wellingtons ended the threat of one of Germany’s early secret weapons of 1939-40.