The delivery of the last ciphering machines of Enigma type was more and more delayed during the years of ongoing World War II, so
engineers of the "Ciphering bureau" of the Swiss Army developed a technically improved ciphering machine based on the rotor principle, which was to be produced by Zellweger AG, Uster.
Theprototypes have been made in 1943 and underwent successful testing with the Signal troops in autumn 1944, the production of a mechanically improved machine was started in spring 1945 in a batch of 640 ciphering machines of the type "NEMA Modell 45". These machines were introduced with the troops and the "Federal Political Department" (Dept. of Foreign Affairs) in 1947 and have been in use for over twenty years.
The NEMA is a mechanical ciphering machine quite similar to the German ENIGMA based on the rotor wheel principle and indication of enrypted letters with a lamp field consisting of 26 small light bulbs. In contrast to the Enigma, the NEMA has a much more complex construction and far better encryption security.
The block of ciphering wheels of the NEMA consist of a reflector wheel which is not moved during operation but only turned in a certain setting according to the encryption key, five advancement wheels and four encrypting rotor wheels. In contrast to the Enigma machine, where the next rotor wheel is moved one position ahead after one complete rotation of the predecessor wheel (like in an odometer), the advancement wheels will move the rotor wheels in irregular intervals, this procedure does greatly improve encryption security.
According to the message key, the advancement wheels and the rotor wheels can be combined in a great number of variations before the set of wheels is inserted in the machine. The message key consists of the combination of wheels in use and the start position position of the single wheels, this key of ten letters will be transmitted in the beginning of each telegram.
When one of the 26 letter keys of the typewriter like keyboard is depressed, the advancement and rotor wheels are advanced in irregular intervals and one of the bulbs in the letter lampfield will be lit, it has to be written down to compose the encrypted message. With the next keystroke, the next letter bulb will be lit. The construction of the machine will assure, that if the same letter key will be depressed several times, the same letter will be encrypted with adifferent letter with everystep of the machine.
The message to be encrypted has to be typed in with the typewriter keybord and the ciphered text has to be copied from the lamp field to a notepad, this note is handed over to the signalman to send it over the airwaves. For the decryption, the received signal code has to be typed in the machine with the correct key settings and the clear message kan be read from the lamp field. The Swiss Nema comes with an additional lamp field which can be connected by a multi pole cable so second operator sitting next to the one doing the keying can copy the text, this procedure speeds up protected message communications when compared to have the same operator doing the keying, reading the lamp field and writing down the letters.
The NEMA machines have been produced by the Apparate- und Maschinenfabrik Uster / Zellweger AG, which had some experience with precision mechanics and electronics, but never had produced any ciphering machines before. All production was done in a secret rated project, only a few experienced female workers did the wiring of the rotor wheels in a secret underground facility. As all equipment crates used by the Swiss Army should carry an external identification to be used at the arsenal, it would not appear as wise to stamp "Secret Ciphering Equipment" on the outside of the crates, it was decided to give them the designation "T.D.", "Tasten - Drücker" which means "Key Press apparatus.
The machines for instruction use (which means these had been used to instruct the operators and were also used for the annual repetition courses) have a different set of code wheels then the machines intended for war use (with a sticker "Nur bei Kriegsmobilmachung abgeben" (to used only in war time)) which come with two additional or spare wheels stored in the lid of the case of the machine. The ciphering machines of the "Federal Political Department" have even another different set of code wheels.
The NEMA machines saw use with the Armed Forces and the "Federal Political Department" from 1948 - 1979. The NEMA procedure was declassified in 1992 (so it was no more classified as secret) and most of the machines were sold to the public at the Meiringen arsenal.
d: Das Fernmeldematerial der Schweizerischen Armee, Band 10, Codes und Chiffrierverfahren, Merker Verlag, Luzern