
The ultimate Japanese encryption machine for diplomatic messages, code-named Purple, included a plugboard. It was the successor to the faulty prototype Red machine, which used a half-rotor switch that needed to be cleaned every day, according to the NSA.
Twenty letters could be plugged and routed through three units of the Purple electromechanical stepping-switch device, while the other six letters went through only one unit.
Credit: National Security Agency



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