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Enigma K
Commercial Enigma A27 · 1927

Enigma K is an electromechanical rotor-based cipher machine, developed in 1927 by Chiffrier­maschinen AG (ChiMaAG) in Berlin (Germany). The device is a member of the glowlamp-based family of Enigma cipher machines and was the successor to the short lived Enigma D (A26). It is also known as Enigma Model A27 and by its designator Ch.11b. The letter 'K' probably means Kommerziell (commercial). Enigma K had the longest life-span of all Enigmas (1927-1944).

Initially, Enigma K had serial numbers starting (confusingly) with the letter A, just like all other models. From 1936 onwards, the serial numbers of the Enigma K were prefixed by the letter K.

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 a by the Swiss Army during and after WWII (Swiss-K).
  

The machine was developed and released in 1927, hot on the heels of the very similar but short-lived Enigma D (A26). It was the first machine on which the notch ring of the rotors was attached to the letter ring rather than to the rotor body. 1 This increased the cipher's strength. Other dif­ferences are the mounting of the power switch and the terminals for an external power supply, as well as the presence of numbers printed above the lamp panel and on the upper row of keys.

Initially, each rotor had a single turnover notch (regular stepping), but on some variants, the number of notches was increased (irregular stepping). For example: Enigma T of 1942 had five notches on each rotor, and the rotors of Enigma KD of 1944 even had nine turnover notches. There are several variants of Enigma K, some of which remained in production until 1944.

  1. Enigma K (Ch.11b) was developed in parallel with the Reichwehr D (Ch.11a), which later became Enigma I). On both machines, the notch ring is attached to the letter ring rather than to the rotor body.

Enigma K variants on this website
Standard commercial Enigma machine model A27
Enigma K with external lamp panel, used by Switzerland.
Special version for Japan with multi-notched rotors
Enigma with multiple-notch rotors and UKW-D
Special version for the German Railways
Standard version
The image below provides a quick overview of the features of the commercial Enigma K. The machine has a keyboard with 26 keys and a lamp panel with 26 lightbulbs, both of which are layed out in the order of a German typewriter (QWERTZ). The machine is powered by an internal 4.5V battery. At the top right is the power knob that allows selection between hell (bright), dkl (dim), aus (off) or Sammler (external power source). To its right are two power terminals.


The machine has four settable rotors, the leftmost of which is the reflector (Umkehrwalze, UKW). The other three are the cipher rotors, each of which has a single turnover notch. When typing, the rotors are driven by pawls and ratchets, resulting in an odometer-style movement. This is known as Enigma Stepping. Under certain circumstances, the middle rotor can make an addional step on two successive key-presses. This misfeature is known as the double stepping anomaly [3].

Inside the lid of the wooden transit case are 10 spare lightbulbs, a green filter that can be placed over the lamp panel, and three metal shields: the oval Enigma logo, the name and address of the manufacturer (ChiMaAG) and a 'made in Germany' shield. These shields were normal on pre-war Enigma machines. The machine shown here (serial number A818) was manufactured in 1927 or 1928 and was sold to a foreign customer (probably in Austria) between 1928 and 1935 [4].

Differences with Enigma D
Compared to its predecessor – Enigma D – the following differences can be observed:

  • Wooden case with box joints 1
  • Two lid retaining brackets (rather than 1)
  • Full width hinge on case lid
  • Metal enclosure around the bare machine
  • Rectangular rotor windows (rather than circular)
  • Power terminals fitted to lid rather than base
  • Power knob fitted to lid rather than base
  • Notch attached to letter ring rather than rotor body
  • Black crackle paint 2
  • Numbers above the lamp panel
  • Letters and numbers on the upper row of keys
  • Die-cast aluminium lamp panel frame
  • Green filter (and hold-down clips on lamp panel)
  • Battery holder box with hinged lid
  1. This refers to the way the side panels of the wooden transit case are joined at the corners.  Wikipedia
  2. Not to be confused with the wrinkle paint used on later machine.

Enigma K (A27) in wooden case
Enigma A27 in wooden case
Enigma K (A27) with serial number A818
A lamp lights up when a key is pressed
Enigma K (A27) interior
Settable UKW and three cipher rotors
Rotors of the Enigma K (A27)
Numbers on the upper row of keys
Power selector and power terminals
Lamp panel hold-down bolt and green filter hold-down clip
Battery
Serial number inside the lower edge of the case lid
Enigma K outside the wooden transit case
Enigma K (A27)
Enigma K
Enigma K (A27)
Enigma K (A27) with open lid
A
×
A
1 / 17
Enigma K (A27) in wooden case
A
2 / 17
Enigma A27 in wooden case
A
3 / 17
Enigma K (A27) with serial number A818
A
4 / 17
A lamp lights up when a key is pressed
A
5 / 17
Enigma K (A27) interior
A
6 / 17
Settable UKW and three cipher rotors
A
7 / 17
Rotors of the Enigma K (A27)
A
8 / 17
Numbers on the upper row of keys
A
9 / 17
Power selector and power terminals
A
10 / 17
Lamp panel hold-down bolt and green filter hold-down clip
A
11 / 17
Battery
A
12 / 17
Serial number inside the lower edge of the case lid
A
13 / 17
Enigma K outside the wooden transit case
A
14 / 17
Enigma K (A27)
A
15 / 17
Enigma K
A
16 / 17
Enigma K (A27)
A
17 / 17
Enigma K (A27) with open lid

Enigma K variants
Swiss-K
In 1939, just before the outbreak of WWII, the Swiss bought Enigma K machines that were used by the Swiss Army, the Air Force and the Foreign Office. These machine have been expanded with an external lamp panel and are therefore housed in a larger wooden transit case.

As these machines were made after 1936, the serial number is prefixed with the letter 'K'.

 More information

  

Enigma KD
This is a special version of the Enigma K that was made for the Militärisches Amt (Abwehr). This machine has a field-rewirable reflector (UKW-D or Dora) and rotors with nine turnover notches each. It therefore features irregular stepping.

Enigma KD first appeared on 3 December 1944 and remained in use throughout the war. At the Enigma Reunion 2009 at Bletchley Park, this Enigma variant was on public display for the duration of the event, courtesy the Swedish FRA.

 More information

  

Railway Enigma
During WWII, the German Railway (Reichsbahn) used a special version of Enigma K, in which the UKW and the rotors were rewired. In addition, the position of the turnover notches of rotors I and III were swapped.

 More information

  

Enigma T   Tirpitz
Enigma T (Tirpitz) was a special version of the Enigma K that was made for the Japanese forces. It was introduced in 1942 and was supplied with 8 rotors with 5 turnover notches each. Further­more, the entry disc (ETW) was wired differently.

The serial numbers of this variant were all prefixed with the letter 'T'.

 More information

  




Wiring
Standard commercial wiring
Below is the wiring for the standard Enigma K variant (A27). This wiring is commonly known as the commercial wiring. Regardless the customer, each Enigma K was supplied with this wiring, unless ordered differently. Note that the wiring of some Enigma K variants, such as the Railway Enigma and Enigma T (see above), was different. See the individual pages for more information.

Rotor ABCDEFGHIJKLMNOPQRSTUVWXYZ Notch Turnover #
ETW QWERTZUIOASDFGHJKPYXCVBNML      
I LPGSZMHAEOQKVXRFYBUTNICJDW G Y 1
II SLVGBTFXJQOHEWIRZYAMKPCNDU M E 1
III CJGDPSHKTURAWZXFMYNQOBVLIE V N 1
UKW 1 IMETCGFRAYSQBZXWLHKDVUPOJN      
 More about rotor wiring

  1. This wiring is measured using the contact at the white dot as the reference point. When the UKW is installed in the machine with its ring setting at 'A' and the letter 'A' visible through the window in the lid, this is the contact just in front of the contact at the top.

UKW removed from the machine - rear view
UKW with dot lined up with the letter 'A'
UKW - contact side
UKW - side view - ring setting at 'A'
UKW - releasing the letter ring
B
×
B
1 / 5
UKW removed from the machine - rear view
B
2 / 5
UKW with dot lined up with the letter 'A'
B
3 / 5
UKW - contact side
B
4 / 5
UKW - side view - ring setting at 'A'
B
5 / 5
UKW - releasing the letter ring

Specifications
Standard version 1
  • Device
    Rotor cipher Machine
  • Brand
    Enigma
  • Type
    K
  • Model
    A27
  • Designator
    Ch.11b
  • Predecessor
    Enigma D
  • Manufacturer
    ChiMaAG (until 1934), H&R (after 1934)
  • Country
    Germany
  • Years
    1927-1944
  • Customers
    Commercial, military, railway
  • Rotors
    3 (removable)
  • Turnovers
    1 per rotor, notch fitted to letter ring 1
  • Reflector
    Settable (26 positions)
  • Wiring
    Commercial
  • Stepping
    Regular (Enigma stepping)
  • Plugboard
    no
  • Extras
    Green filter
  • Dimensions
    290 × 280 × 155 mm (incl. wooden case)
  • Weight
    2.4 kg (incl. wooden case)
  1. The specifications of some Enigma K variants may be different. See the individual pages for additional information.

Nomenclature
  • Enigma K
  • A27
  • Ch.11b
  • Commercial Enigma
Known serial numbers 1
  • A793
  • A794
  • A795
  • A796
  • A805
  • A806
  • A807
  • A808
  • A809
  • A810
  • A811
  • A812
  • A813
  • A814
  • A815
  • A817
  • A818
  • A819
  • A820
  • A821
  • A822
  • A824
  • A830
  • A831
  • A832
  • A833
  • A834
  • A835
  • A836
  • A1247
  • A1248
  1. Numbers taken from a list of 21 October 1935 from H&R, with commercial machines — Enigma K (A27) — delivered to foreign countries. Information provided by Frode Weierud [4].

Surviving machines 1
  • A818
    Crypto Museum, Netherlands
  1. Swiss Enigma K machine are not listed here.

Documentation
  1. Enigma K instruction manual (German) 1
    ChiMaAG, 1933. Issued with Enigma A833.
  1. There are different versions of this booklet. The machine shown on the first page is probably an Enigma D, whilst the machine shown in the fold-out at the back, is clearly an Enigma K.

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

    Cryptologia, July 1998, Volume XXII, Number 3.

  2. Paul Reuvers and Marc Simons, Wiring of Enigma A818
    Crypto Museum, October 2011.

  3. David Hamer: Actions involved in the 'double stepping' of the middle rotor 1
    Cryptologia, January 1997, Volume XX, Number 1.

  4. Frode Weierud, Personal correspondence
    Early Enigma K history. September 2011.
  1. Reproduced here by kind permission from the author.

Further information
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© Crypto Museum. Created: Monday 14 September 2009. Last changed: Tuesday, 19 March 2024 - 17:47 CET.
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