Swiss K Enigma
note remote lampboard and lack of plugboard
The NEMA Cipher Machine (NEue MAschine) was developed by the Swiss Army during WW2 to replace the commercial Enigma machine then in use,
which was called the Swiss K Enigma. This was the commercial version of the German Enigma machine without a plugboard, which was known to
have been broken by both Allied and German codebreakers. Development of the NEMA began between 1941 and 1943, borrowing heavily from the
Enigma machine with the use of rotors, reflector and lamp board. Production began in April of 1945, just a month before the end of the war
in Europe. Zellweger AG manufactured 640 NEMAs, with the first machines entering service in 1947.
The NEMA was also called the T-D Machine (Tasten-Drücker-Maschine which means key-stroke machine) and had serial numbers from 100 to 740.
The first 100 machines were used by the diplomatic service. The next 220 machines were used by the Army for training purposes. The last
320 machines had labels stating they were only to be used in case of war.
The NEMA uses 10 rotor wheels, 4 are standard letter transposition wheels and a fifth wheel is a reflector wheel, like the reflector used
in the enigma. The reflector transposes pairs of letters, so if a "B" is converted to a "T" then a "T" will convert to a "B". This allows
the machine to be used for ciphering and deciphering using the same key settings. It also means that no letter will cipher onto itself, a
vulnerability it shares with the Enigma machine. Each of these 5 cipher wheels are paired with a "drive" wheel which sets the stepping motion
of each wheel. So, each cipher wheel has a unique stepping motion and does not suffer from the same vulnerability caused by the "odometer"
style of stepping motion of the Enigma. As in the Enigma machine, pressing a typewriter-like key will light up a letter on the lamp board,
which must be written down. A detached lamp board and a connection to an IBM Selectric typewriter were also available.
The training machines were issued with a complete set of 10 rotors, the Army machines held in reserve used the same 5 cipher wheels plus 2
additional wheels were available for use and stored in the lid. There were also 7 drive wheels, none of which matched the drive wheels of
the training machines. Not much in known about the 100 diplomatic machines, but they most likely used different stepping wheels from either
of these Army machines and may have also used different cipher wheels.
The NEMA enciphered the 26 letters of the alphabet without the use of numbers, spaces or other characters. The operators of the machine were
instructed to use the top line of letters on the keyboard "QWERTZUIOP" as the numbers "1234567890" when each number is preceded by a "Y" and a
"Y" is also used between each number. After the last number, then an "X" is entered to indicate a return to letters. An "X" was also to be
used when absolutely required for a space. The operator was to send a random 10 letter word at the beginning and end of the message which
identifies the wheel setting for the receiving NEMA for the rest of the message. This 10 letter key was sent in the clear, which gives a
stronger cipher since this did not contribute to breaking the code, as was the case with the German Enigma.
While the NEMA cipher machine corrected the "odometer stepping" of the Enigma and the operators did not encode the message key, there were some
anomalies with the stepping wheels that jeopardized the security of this machine. Depending on the setting of the wheels, there could be a
surprisingly small message depth, meaning that the same cipher alphabet was used within a message, sometimes on a cycle of every 26 letters.
In some cases, three letters in a row would use the same cipher alphabet (meaning none of the wheels would advance) and this would repeat
every 26 letters!
The Swiss Army most likely knew of the vulnerabilities of the NEMA and may have continued to use it for tactical messages, as the US did with
the similarly vulnerable M-209. The strength of the NEMA cipher was definitely questionable after 1974, when the British announced they
broke the Enigma code during WW2. The Swiss Army quit using the NEMA in 1975 but kept them for emergency purposes. The 540 Army NEMAs were
declassified on July 9, 1992, and were offered for sale to the public on May 4, 1994. The diplomatic NEMA machines have presumably been
destroyed. Pictured below is a NEMA machine, serial number 642, reserved for war use and therefore in unused condition.
See the Entire Collection of Cipher Machines
See detailed pictures of the Swiss NEMA cipher machine