The American Naval Bombe N-530

Menu Switches

In Chapter 03, I described a full Letchworth Enigma with four sets of brush holders and two sockets where the reflector cable assemblies would be connected. What may not be clear is where the two other Jones Plugs went.


These plug into the Switch Bank above the Enigma. Enigmas 1 to 8 in the front and 9 to 16 on the rear


There are two similar switch units; the only difference being that on the upper, the rotary switches are brought to the front of the machine.

The 26 sockets on the end of wheel banks can be considered the internal termination or busses running the length of the unit. Switches are rotated to a position that connects the Letchworth input and output to busses as defined by the menu. These settings are worked out prior to sending the job to the WAVES: this together with information about which wheels to mount and their rotation displacement.

The output of each unit is connected by the way that the cable assemblies going to the diagonal board are connected in parallel

The image above is a closer look with, for example, Enigma 13 set to 09, 10.

In the table below the switches above each enigma are set as shown. All other enigmas are set to OFF

Identify the output BUS for each of the 11 Nodes

Wheel offsets are as Peggy

Nodes are – N L G E U H Z R V A S

These 11 will be the outputs to the DB sockets.

On our BTM British machine menu diagrams, the connections to the diagonal board are not shown because it is known that these connections are always made directly to the relevant letter.

The in and out connections to the Letchworth Enigmas plug into the Switch Bank above. The sockets for the lower bank are next to the 26-way switches whereas the sockets for the upper bank are on the rear.

The rotary switches connect an enigma in and out cable to one of the output lines or ‘busses’ that connect to 26 sockets on the end of the switch banks where cables to the diagonal board are plugged.

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