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Rotor Switzerland Enigma K PSU → NEMA →
Enigma K variant used by Switzerland
The Swiss Enigma K, commonly known as Swiss-K, 1 was a variant of the
Enigma K that was used throughout World War II (WWII) by neutral
Switzerland.
The machines were ordered by the Swiss Army well before the start of the war,
the first batch of which was delivered in 1939. A total of 265 machines were
used by the Swiss Army, the Swiss Air Force and the Foreign Ministry [2].
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Unlike other Enigma models, the Swiss-K was housed in a wider wooden
case that was made by the Swiss themselves.
Apart from the Enigma-K, it also accomodates an external lamp panel
(German: Lesegerat) and maintenance tools.
The lock at the front of the case is identical to that on other
Enigma cases, but two metal brackets are mounted to the right of the lock,
allowing an additional padlock to be used.
Inside the top lid of the case are the usual accessories, such
as the green lamp filter and the spare light bulbs.
Also present in the lid is a small metal clip – similar to the one on a clipboard –
that is used here as a copy holder.
Just above the lamp filter is a wooden stub to ensure
that the power selector is in the OFF position before the case is closed.
If it is in the wrong position, the case cannot be closed.
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The Swiss started using Enigma in 1938, when they received 14 standard
commerical Enigma K machines and another 65 in 1939.
Finally, in 1940, a large number of machines were supplied in two batches
(5 May and 10 July). These are the machines that became known as the
Swiss Enigma K [1].
By July 1942, a total of 265 machines was in use: 102 by the Swiss Army
and 163 by the Air Force [2][3].
The machines of the Foreign Ministry were on loan from the Army.
Initially, all machines were supplied with the
standard commercial wiring
known from Enigma D and Enigma K.
For security reasons they were later rewired
by the Swiss. The machines were decommissioned in 1946 when
they were succeeded by the Swiss-developed NEMA.
They were reused in 1953 however, when Switzerland was monitoring the
armistice line between North and South Korea on behalf of the United Nations
[4]. It is likely that these machines were modified.
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-
Not the official name, but used by researchers
and historians to disciminate it from other K-variants.
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Differences with standard Enigma K
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After delivery of the Enigma K machines from the manufacturer,
the following modifications were carried out by the
Kriegsmaterialverwaltung (War Material Procurement) [2]:
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- Addition of an extra lamp panel to most of the machines (see below).
- A transformer was added in order to save batteries (PSU, see below).
- The rotor stepping mechanism of the machines used by the Swiss Army was modified.
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The wooden case of the Swiss-K Enigma was probably made by the Swiss
themselves and is wider than usual.
The extra space is used for the second lamp panel that is shown below.
The additonal lamp panel is connected directly to the Enigma machine
and can not be removed.
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The extra lamp panel can be removed from the wooden box and placed elsewhere
on the table. It was used by an officier, or an additional cipher clerk,
to write down the message that was being deciphered by the Enigma operator.
If necessary, the green lamp filter could be fitted on the external panel.
Below the extra lamp panel is a small space that is used to store the
maintenance attributes, such as a pinsel and a piece of cloth. The rather long
textile encapsulated cable from the Enigma to the lamp panel is also stored
in this space.
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The extra lamp panel was not supplied by the Enigma manufacturer
(Heimsoeth und Rinke), but were built to order by the optical
Werkstatten H. Bischhausen in Switzerland.
A similar external lamp panel is present on the later Swiss-made
NEMA cipher machine.
The NEMA was designed to replace the Swiss-K Enigma, after the Swiss found out
that their messages were being read by the Germans (and the allied forces).
Although the Swiss-K Enigma is the only machine to be supplied with the
extra lamp panel directly attached to the machine, a similar attachment was
available for other lamp-based Enigma machines. This was the so-called
Lesegerät (read-out device).
It required all lamps of the Enigma to be removed, and a large connector to
be fitted instead. It was primarily intended for the Enigma M4
that was used by the U-Boot section of the German Kriegsmarine (Navy).
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Although the Swiss-K Enigma could be powered with a standard 4.5V Wehrmacht
battery, it was supplied with an external Power Supply Unit (PSU).
The PSU was not built by the Enigma manufacturer, but by the Swiss company
H. Stucki Transformatorenbau in Bern (Switzerland).
The external power supply allowed four Enigma machines to be connected
simultaneously.
➤ More information
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It is often though that the Enigma-K is a 4-rotor machine. Although there
are clearly four rotors visible on the body of the machine, only the rightmost
three of them are the actual cipher rotors that move during encipherment.
The leftmost rotor is the Umkehrwalze (reflector) that can be set to
any of 26 positions at the start of the encoding process. The UKW doesn't
move during encipherment.
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Like in other Enigma machines, the three cipher rotors are mounted on a shaft
that is usually called the drum (see the image on the right).
As with other non-Wehrmacht Enigma machines, the rotors have letters on
their circumfere, rather than numbers.
Each rotor has a single notch to control the stepping of the next rotor,
but the position of the notch was different on each rotor,
just like on its predecessor, the commercial Enigma D (see
the table below). The position of the notches was never changed.
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The UKW (reflector) of the Enigma K can easily be removed from the machine,
simply by taking it off its small shaft at the left, unlike the UKW of a
Wehrmacht Enigma. Like on the Enigma D, the UKW
can be set to any of 26 positions at the start of the encoding process.
It does not move during encipherment.
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All Enigma K machines were delivered by the Germans with the standard
commercial rotor wiring, also known from the Enigma D
(see the table below).
Immediately after reception, however, the Swiss changed the wiring of
all cipher rotors.
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| Rotor | ABCDEFGHIJKLMNOPQRSTUVWXYZ | Notch | Turnover | # |
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| ETW | QWERTZUIOASDFGHJKPYXCVBNML | |
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| I | LPGSZMHAEOQKVXRFYBUTNICJDW | G | Y | 1 |
| II | SLVGBTFXJQOHEWIRZYAMKPCNDU | M | E | 1 |
| III | CJGDPSHKTURAWZXFMYNQOBVLIE | V | N | 1 |
| UKW | IMETCGFRAYSQBZXWLHKDVUPOJN | |
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Although the Swiss altered the wiring of the cipher rotors (I, II and III),
the wiring of the ETW and UKW was left unchanged. This is true for all
three users of the Enigma K: the Swiss Army, the Air Force and the Foreign
Ministry (diplomatic service).
In the table below, the only known wiring of the rotors of the Swiss Air Force
are given. The wiring of the other services are unknown to us.
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| Rotor | ABCDEFGHIJKLMNOPQRSTUVWXYZ | Notch | Turnover | # |
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| ETW | QWERTZUIOASDFGHJKPYXCVBNML | |
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| I | PEZUOHXSCVFMTBGLRINQJWAYDK | G | Y | 1 |
| II | ZOUESYDKFWPCIQXHMVBLGNJRAT | M | E | 1 |
| III | EHRVXGAOBQUSIMZFLYNWKTPDJC | V | N | 1 |
| UKW | IMETCGFRAYSQBZXWLHKDVUPOJN | |
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In 1941, the Swiss found out that the French had broken some of their Enigma traffic.
The machines used by the Swiss Army were subsequently modified by altering the
stepping mechanism. The rightmost rotor was made stationary and the middle rotor
was made to step with every key press [2]. The leftmost rotor and the UKW would follow
in the normal fashion (Enigma stepping).
This modification was only present on the Swiss Army machines and not on the machines
used by the Air Force and the Foreign Ministry.
Another safety measure was to rewire the cipher rotors regularly. The machines used
by the Foreign Ministry were apparently rewired every two years. Despite this,
their Enigma traffic remained to be broken by the allied code breakers.
At BP, Colonel Tiltman was able to read Swiss diplomatic traffic from September
1939 onwards [1] whilst the Americans took care of the Swiss codes
in their part of the world.
The Germans also broke the Swiss diplomatic codes and were able to read their
traffic from 1939 onwards, right until the end of the war [5].
As this was known by the Swiss, they started to develop their own machine.
They called it NEMA,
for Neue Maschine (new machine).
Unfortunately for the Swiss, the machine came too late. It was introduced in
1946, just after the war had ended.
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Device Cipher machine Brand Enigma Type K Model A27 (modified) Designator Ch.11b Manufacturer H&R Country Germany Years 1939-1940 Customers Swiss Army, Swiss Air Force, Swiss Foreign Ministry (diplomatic service) Rotors 3 Turnovers 1 per rotor Reflector Settable Wiring Modified by the Swiss Stepping Standard (Enigma stepping) Plugboard no Extras Lesegerät (external lamp panel) Case Wood, extra compartment for Lesegerät Quantity 265
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- Enigma K
- Swiss Enigma K
- Swiss-K
- A27
- Ch. 11b
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K769 Günter Hütter, Austria K774 Crypto Museum, Netherlands K776 Private collector, Switzerland K779 Glen Miranker, USA K787 Crypto Museum, Netherlands
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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.
- Rudolf J. Ritter, Zu den frühen Maschinen-Schlüsselverfahren in der Schweiz
Rheineck, 16 January 1996.
- Rudolf J. Ritter, Das Fernmeldematerial der Schweizerischen Armee seit 1875
Volume 10, General Staff, Bern 2002.
- Dominik Landwehr, The cipher machine Enigma and Switzerland
14 February 2020, updated 1 September 2020.
- Christos, Triantafyllopoulos,
The compromise of the Swiss diplomatic Enigma K cipher machine in WWII
Blog: Christos military and intelligence corner. 1 October 2017.
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© Crypto Museum. Created: Monday 12 April 2010. Last changed: Monday, 28 July 2025 - 06:33 CET.
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