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Swiss-K
Enigma K variant for Switzerland

The most famous and well-known Enigma K variant is probably the version that was built for the Swiss Army. 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.
 
The image on the right shows a typical Swiss Enigma K machine. It's a standard Enigma K that is mounted inside a rather uncommon oak wooden box that is wider than a usual Enigma case. The extra space is used to store an additional lamp panel (see below).

The lock on the case (used to keep it closed) is identical to that on other Enigma boxes, 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 oak wooden box are the usual accessories, such as the green lamp filter and the spare light bulbs. Also present in the lid is a small metal clamp to allow a message form to be clipped-in.

Just above the lamp filter is a small wooden stub to ensure that the power switch (rotary) is in the OFF-position before the case is closed.
  
Swiss-K Enigma (open)

The Swiss started to use the Enigma machine in 1938, when they received 14 Enigma D machines. Another 65 machines were ordered in 1939. Finally, in 1940, a large number of machines were supplied in two batches (5 May and 10 July). These were the machines we now known as the Swiss-K [1] .

In July 1942, a total of 265 machines was in use, 102 by the Swiss Army and 163 by the Air Force [2] . The machines of the Foreign Ministry were on loan from the Army. Initially, they were all supplied with the standard commercial wiring known from the Enigma D. The Swiss, however, rewired their machines frequently.
 
Swiss-K Enigma case (closed) Swiss-K Enigma (open) The contents of the wooden box. The Enigma-K at the left and an additional lamp panel at the right. A view at the wheels. The leftmost wheel is the settable reflector (UKW) Power switch and serial number The top lid of the wooden box which is also the storage place for the spare light bulbs, the paper clip and the green lamp filter. Wooden stub to ensure that the power switch is OFF before the lid can be closed Lock of the Enigma-K case
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Swiss-K Enigma case (closed)
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Swiss-K Enigma (open)
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The contents of the wooden box. The Enigma-K at the left and an additional lamp panel at the right.
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A view at the wheels. The leftmost wheel is the settable reflector (UKW)
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Power switch and serial number
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The top lid of the wooden box which is also the storage place for the spare light bulbs, the paper clip and the green lamp filter.
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Wooden stub to ensure that the power switch is OFF before the lid can be closed
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Lock of the Enigma-K case

Modifications
After delivery of the Enigma K machines from the manufacturer, the following modifications were carried out by the Kriegsmaterialverwaltung (War Material Procurement) [2] :
 
  • 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 wheel stepping mechanism of the machines used by the Swiss Army was modified.
Extra lamp panel
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.
 
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.
  
External lamp panel

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).
 
The external lamp panel aside the Enigma-K External lamp panel External lamp panel Lock of the external lamp panel Opening the external lamp panel External lamp panel (open) Interior of the external lamp panel External lamp panel storage place
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The external lamp panel aside the Enigma-K
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External lamp panel
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External lamp panel
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Lock of the external lamp panel
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Opening the external lamp panel
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External lamp panel (open)
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Interior of the external lamp panel
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External lamp panel storage place

Power Supply Unit
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
  

 
Wheels
It is often though that the Enigma-K is a 4-wheel machine. Although there are clearly four wheels visible on the body of the machine, only the rightmost three of them are the actual coding wheels that move during encipherment. The leftmost wheel 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.
 
Like in other Enigma machines, the three coding wheels 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 wheels have letters on their circumfere, rather than numbers.

Each wheel has a single notch to control the stepping of the next wheel, but the position of the notch was different on each wheel, just like on its predecessor, the commercial Enigma D (see the table below). The position of the notches was never changed.
  
The three coding wheels

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.
 
Typical view of the lamp panel and the wheels, after opening the cover. The wheels of the Swiss-K Enigma Umkehrwalze (reflector) Eintrittswalze (entry wheel) The stubs and the mounting latch at the rear of the UKW The stubs and the mounting latch at the rear of the UKW The spring-loaded contacts of the reflector (UKW) The UKW removed from the machine
The three coding wheels The three coding wheels The three coding wheels Close-up of the spring-loaded contacts of one of the wheels Close-up of the flat-faced contacts of one of the wheels
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Typical view of the lamp panel and the wheels, after opening the cover.
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The wheels of the Swiss-K Enigma
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Umkehrwalze (reflector)
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Eintrittswalze (entry wheel)
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The stubs and the mounting latch at the rear of the UKW
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The stubs and the mounting latch at the rear of the UKW
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The spring-loaded contacts of the reflector (UKW)
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The UKW removed from the machine
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The three coding wheels
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The three coding wheels
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The three coding wheels
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Close-up of the spring-loaded contacts of one of the wheels
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Close-up of the flat-faced contacts of one of the wheels

Wiring
All Enigma K machines were delivered by the Germans with the standard commercial wheel wiring, also known from the Enigma D (see the table below). Immediately after reception, however, the Swiss changed the wiring of all cipher wheels.

Standard commercial wiring
 
Wheel ABCDEFGHIJKLMNOPQRSTUVWXYZ Notch Turnover #
ETW QWERTZUIOASDFGHJKPYXCVBNML      
I LPGSZMHAEOQKVXRFYBUTNICJDW G Y 1
II SLVGBTFXJQOHEWIRZYAMKPCNDU M E 1
III CJGDPSHKTURAWZXFMYNQOBVLIE V N 1
UKW IMETCGFRAYSQBZXWLHKDVUPOJN      

Although the Swiss altered the wiring of the cipher wheels (I, II and III), the wiring of the UKW (reflector) 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 wheels of the Swiss Air Force are given. The wiring of the other services are unknown to us.

Swiss Enigma K Wheel Wiring (Swiss Air Force) [1]
 
Wheel ABCDEFGHIJKLMNOPQRSTUVWXYZ Notch Turnover #
ETW QWERTZUIOASDFGHJKPYXCVBNML      
I PEZUOHXSCVFMTBGLRINQJWAYDK G Y 1
II ZOUESYDKFWPCIQXHMVBLGNJRAT M E 1
III EHRVXGAOBQUSIMZFLYNWKTPDJC V N 1
UKW IMETCGFRAYSQBZXWLHKDVUPOJN      

 
Breaking the Swiss-K
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 wheel was made stationary and the middle wheel was made to step with every key press. The leftmost wheel 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 wheels 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. 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.
 
References
  1. David Hamer, Geoff Sullivan and Frode Weierud
    Enigma Variations: An Extended Family of Machines

    Cryptologia, July 1998, Volume XXII, Number 3.

  2. Rudolf J. Ritter, Das Fernmeldematerial der Schweizerischen Armee seit 1875
    Volume 10, General Staff, Bern 2002.

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Crypto Museum. Created: Monday 12 April 2010. Last changed: Monday, 12 June 2017 - 20:22 CET.
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