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Enigma K
A family of commercial machines A27

In 1927, developments were started to create improved versions of the commercial Enigma D machine. One of the most important offsprings was the Enigma K that was given the model number A27 and internal designator Ch. 11b. The letter 'K' was probably used for the German word Kommerziell (commercial). Apart from a few manufacturing modifications, this machine is identical to the Enigma D. The machine was supplied to a variety of (international) customers.
 
Initially, all machines had serial numbers starting (confusingly) with the letter A, and it wasn't until 1936 that the letter K was used as a prefix for the serial numbers of these machines.

Many Enigma K machines were built for German users, such as the Reichsbahn (railway), but they were also sold to a number of foreign users. It is known that the Italian Navy (Supermarina) used Enigma K machines throughout WWII. Modified versions of the Enigma K were also used during the Spanish Civil War (1936-1939) and another one by the Swiss Army during and after WWII.
  
A view at the wheels. The leftmost wheel is the settable reflector (UKW)

Initially, each wheel had a single turnover notch (regular stepping), but in later variants, the number of notches was increased. The Enigma T (1942), for example, had 5 notches on each wheel and the wheels of the Enigma KD (1944) even had 9 turnover notches (irregular stepping).
 
Enigma K variants
  • Enigma K (1927)
    This is the standard model that was introduced in 1927 as the successor to the Enigma D. It is also known as A27 or as Ch.11b. It is functionally identical to the Enigma D. The serial numbers initially started with an A, but from 1936 onwards the prefix K was used.

  • Swiss Enigma K variant (1938)
    This was a standard Enigma K machine that came with an external lamp panel and a separate power supply. The wheels were rewired by the Swiss and on some machines the wheel turnover system was modified slightly. It has a larger wooden case that was made by the Swiss. The serial numbers of all Swiss machines were prefixed by the letter 'K'.

  • Enigma T (Tirpitz) (1942)
    Special version designed for the Japanese forces in 1942. It was supplied with 8 cipher wheels with 5 turnover notches each. All serial numbers started with the letter T.

  • Enigma KD (1944)
    Special version of the Enigma K, developed in 1944 for Mil Amt. It had three wheels with 9 turnover notches each, and a rewirable reflector, known as UKW-D (Dora).

  • Reichsbahn (Railway) Enigma
    This was a common Enigma K that was rewired especially for the German Railway, the Reichsbahn. On this machine the notches of wheels I and III have been swapped.

Wheel Wiring
The wiring of the wheels of the standard Enigma K was identical to the wiring of the Enigma D. This suggests that the machine was initially intended for commercial customers. The standard commercial wiring is given in the table below.
 
Wheel ABCDEFGHIJKLMNOPQRSTUVWXYZ Notch Turnover #
ETW QWERTZUIOASDFGHJKPYXCVBNML      
I LPGSZMHAEOQKVXRFYBUTNICJDW G Y 1
II SLVGBTFXJQOHEWIRZYAMKPCNDU M E 1
III CJGDPSHKTURAWZXFMYNQOBVLIE V N 1
UKW IMETCGFRAYSQBZXWLHKDVUPOJN      

 
Swiss-K
The most famous and well-known Enigma K variant is probably the version that was built for the Swiss. Although it is not an official name, this machine is often called the Swiss-K.

The machines were ordered by the Swiss before WWII and the first batch was delivered in 1939.

 More information
  
The contents of the wooden box. The Enigma-K at the left and an additional lamp panel at the right.

 
Enigma KD
This machine was based on the standard commercial Enigma K, but had differently wired wheels and a rewirable reflector (UKW-D). It first appeared on 3 December 1944 and remained in use throughout the rest of the war by the German Militärisches Amt (Abwehr).

During the Enigma Reunion 2009 we were able to see the Enigma KD for the first time.

 More information
  

 
Railway Enigma
During WWII, the Germans used a special Enigma machine for the German Railway (Reichsbahn). It basically was a standard Enigma K with rewired wheels and a rewired UKW. Furthermore, the position of the notches of wheels I and III were swapped.

 More information
  
Commercial Enigma used by the German Railway (Reichsbahn)

 
Enigma T (Tirpitz)
The Enigma T, codenamed Tirpitz, was developed during WWII by the Germans especially for use by the Japanese Army.

It was based on the commercial Enigma K, but had differently wired wheels and multiple turnovers on each wheel. Furthermore, it had an Eintrittswalze (ETW) that was wired differently than all other Enigma machines.

 More information
  

 
References
  1. David Hamer, Geoff Sullivan and Frode Weierud
    Enigma Variations: An Extended Family of Machines

    Cryptologia, July 1998, Volume XXII, Number 3.

Further information

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Crypto Museum. Created: Monday 14 September 2009. Last changed: Monday, 12 June 2017 - 20:20 CET.
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