The Swiss NEMA is an electromechanical wheel-based cipher machine that was developed by Zellweger AG in Uster Switzerland during World War II as a replacement for the German Enigma model “K” that was being used by the Swiss Army. NEMA is the abbreviation of NEue MAchine (New Machine). The machine is also known as T-D, which stands for Tasten-Drücker Maschine (key-press machine).

During WWII, the Swiss Army used a modified version of the German-made commercial Enigma model “K” machine . After the Swiss discovered that their Enigma “K” traffic was being read by both the Allied forces and the Germans, they started the development of their own improved machine, which they called NEMA.

The NEMA machine is based on the Enigma machine and at first glance it appears to have 10 wheels, but only 5 of them are electrically wired. Four of these are the coding wheels, with 26 contacts at either side, just like on the German Navy Enigma

The 5th wired wheel (at the left) is the reflector which is moved during encipherment unlike the reflector of the Enigma model “K”, which can be set, but does not move. The other 4 wheels are the stepping-wheels. They are mounted on the axle in pairs with the coding wheels. Each stepping-wheel has several mechanical notches that control the turnover of the adjacent wired coding wheel.

Like the Enigma, the NEMA has a lamp panel with the 26 letters of the alphabet (A-Z). These lamps match with 26 of the keys on the keyboard (A-Z), but unlike Enigma, the NEMA has some additional keys to toggle between letters (BU) and numbers (ZL), and for carriage return (WR). Like the spacebar, these keys were only used when connected to an electric typewriter or a teleprinter (teletype).

The machine contains several improvements over the Enigma design and is difficult to break even by today’s standards. It features, for example, irregular stepping produced by the addition of the stepping-wheels associated with each wired rotor. This makes the machine far less predictable than an Enigma “K”. But it has also inherited some of the weaknesses of the Enigma such as the fact that a letter can never be enciphered into itself. The NEMA has no plugboard but has instead a movable reflector.

The NEMA also includes a remote lighted-letter panel that can be positioned so that only an officer can read the deciphered messages.

The NEMA cipher machine was developed between 1941 and 1943 and the first prototype was ready in early 1944. After a few modifications and improvements, the machine was finally approved in March 1945. Production started in 1946, with the first machines entering service in 1947. The NEMA was used by the Swiss Army in the years following WW II, and by the Diplomatic Service.