A three wheel Bombe used to break a three wheel German Army or Airforce Enigma needs five drums types; if German surface fleet another three.

To allow our machine to be configured to any possible combination of Army or Airforce, 36 of each drum type are required. We made 12 for the surface fleet

Below all basic five are shown and identified in the manner that the Germans used for the basic five with a few sample links fitted.

John Lewis has been almost solely responsible for fitting the wire and solid links to all drums. With 104 connection of one type or another on each drum this adds up to more than 20,000 connections in total. A formidable task in its own right.

It should be noted that before links are added the protective skirt has been fitted. This is just visible. This keeps the brushes from being damaged so long as they are placed on a flat surface.

Not all the links inside the drums are wire. Many are solid copper ‘figure of 8’ items. These were too labour intensive to make ourselves when we considered alternatives. Photo Etching proved to be a very effective and not overly expensive solution. However it did rely on Computer Aided Design files being available but, we had already produced these much earlier in the Rebuild. The finished items came in sheets where they could very easily be snipped out ready to fit without further processing.

Two examples are shown below.

The linking wires needed a small spade clip at each end so here was another labour intensive activity that the team carried out. Not only was it essential that wires were fitted correctly but due to the limited space available excess length had to be avoided. Therefore wiring charts and schedules were produced as shown below to ease the repetitive effort and to act as a check list. A range of wire link lengths were established and the appropriate one indicated on the schedule.

Final Assembly and Testing

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