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Enigma Tree A28 → KD → Swiss-K → T → Railway → ← D
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).
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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).
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The machine was developed and released in 1927, hot on the heels of
the nearly identical 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, and the presence of
digits 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.
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This is not entirely certain.
It is also possible that the notch ring was first attached to the
letter ring on the Reichwehr D (which later became
Enigma I), as it was developed around the same time as the Enigma K.
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Enigma K variants on this website
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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].
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Differences with Enigma D
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Compared to its predecessor – Enigma D – the following differences
can be observed:
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- Wooden case with box joints 1
- Rectangular windows
- 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
- Green filter
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This refers to the way the side panels of the wooden transit
case are joined at the corners. ➤ Wikipedia
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Not to be confused with the wrinkle paint used on later machine.
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A
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
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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
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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 wheels I and III were swapped.
➤ More information
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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
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Standard commercial wiring
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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.
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Wheel
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ABCDEFGHIJKLMNOPQRSTUVWXYZ
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Notch
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Turnover
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#
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ETW
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QWERTZUIOASDFGHJKPYXCVBNML
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I
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LPGSZMHAEOQKVXRFYBUTNICJDW
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G
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Y
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1
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II
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SLVGBTFXJQOHEWIRZYAMKPCNDU
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M
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E
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1
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III
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CJGDPSHKTURAWZXFMYNQOBVLIE
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V
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N
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1
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UKW
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IMETCGFRAYSQBZXWLHKDVUPOJN
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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 wheel, 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)
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The specifications of some Enigma K variants may be different. See the
individual pages for additional information.
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- Enigma K
- A27
- Ch.11b
- Commercial Enigma
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- A793
- A794
- A795
- A796
- A805
- A806
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- A807
- A808
- A809
- A810
- A811
- A812
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- A813
- A814
- A815
- A817
- A818
- A819
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- A820
- A821
- A822
- A824
- A830
- A831
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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].
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A818 Crypto Museum, Netherlands
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Swiss Enigma K machine are not listed here.
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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.
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- David Hamer, Geoff Sullivan and Frode Weierud
Enigma Variations: An Extended Family of Machines
Cryptologia, July 1998, Volume XXII, Number 3.
- Paul Reuvers and Marc Simons, Wiring of Enigma A818
Crypto Museum, October 2011.
- David Hamer: Actions involved in the 'double stepping' of the middle rotor 1
Cryptologia, January 1997, Volume XX, Number 1.
- Frode Weierud, Personal correspondence
Early Eniga K history. September 2011.
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Reproduced here by kind permission from the author.
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© Crypto Museum. Created: Monday 14 September 2009. Last changed: Friday, 25 November 2022 - 10:45 CET.
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