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Enigma I
The Service Enigma Machine

In 1926, the German Army - then called the Reichswehr - adopted the lamp-based Enigma machine, or Glühlampenmaschine as it was then called. In early 1927, the first machine with an single-ended Steckerbrett (plug board) was developed. Later that year, the final version was released, with an improved double-ended Steckerbrett. It was based on the chassis of the Enigma D and was given the internal designator Ch. 11a. The first batch of machines (approx. 600 units) were delivered on 10 December 1927. The Rechswehr (the predecessor of the Wehrmacht) called this machine the Enigma I. All further German Army Enigma machines would be based on that design.
 
This version of the Glühlampenmaschine (lamp machine) has three moving code wheels, a fixed reflector (UKW) and a Steckerbrett (plug board). The Steckerbrett was used exclusively for the German Army.

It was supplied with 5 different coding wheels, numbered I to V. Each wheel had 26 positions and had numbers (01-26) on the circumfere. The wiring of each wheel is given below.

About 20,000 machines of this type were manufactured by various manufacturers, but only a hand full have survived.
  
Click to enlarge

The Enigma I was used by both the Wehrmacht (Army) and the Luftwaffe (Airforce). It was later adopted by the Kriegsmarine (German Navy) where it was commonly known as the M3 (preceeded by the M1 and the M2). The only obvious differency between the Army version and the Navy version is that the wheels of the latter have letters (A-Z) rather than numbers.

The machine is known by different names:
  • Wehrmacht Enigma
  • Heeres Enigma
  • Army Enigma
  • Service Enigma
  • Army/GAF Enigma
  • 3-wheel Enigma
  • 3-wheeler
but the official name for it is Enigma I (Roman number 1) or Ch.11a.
 
Enigma Enigma Front View Serial Warning Steckerbrett The

 
Extra wheels
The Enigma I was supplied with 5 coding wheels, but only 3 of them were in the machine at any time. Each day, the operator would place 3 wheels in the machine in a particular order, as instructed by the codebook.
 
The remaining two (unused) wheels were stored in a small wooden box. The image on the right shows an example of such a storage box with two wheels.

In the picture, wheels I and V are currently stored inside the box, whilst wheels II, III and IV are fitted in the machine.

Other types of boxes are known to exist, but this is the most common model.
  
Click to enlarge

 

 
Enigma Uhr
During WWII, the Germans made several attempts to make the Enigma more secure.

In July 1944, the German Luftwaffe came up with a smart device called Enigma Uhr, which was introduced without any prior warning whatsoever. It was attached to the side of an Enigma I and connected directly to the Steckerbrett.

 More information
  

 
Wiring
Below is the wiring for each wheel, the ETW and all three known UKWs. UKW-A was used before WWII [1]. UKW-B was the standard reflector during the war and UKW-C was only temporarily used during the war. The wiring of all 5 wheels is identical to the wiring of the first 5 wheels of the Enigma M3 (used by the Kriegsmarine) and the U-Boot Enigma M4.
 
Wheel ABCDEFGHIJKLMNOPQRSTUVWXYZ Notch Turnover #
ETW ABCDEFGHIJKLMNOPQRSTUVWXYZ      
I EKMFLGDQVZNTOWYHXUSPAIBRCJ Y Q 1
II AJDKSIRUXBLHWTMCQGZNPYFVOE M E 1
III BDFHJLCPRTXVZNYEIWGAKMUSQO D V 1
IV ESOVPZJAYQUIRHXLNFTGKDCMWB R J 1
V VZBRGITYUPSDNHLXAWMJQOFECK H Z 1
UKW-A1 EJMZALYXVBWFCRQUONTSPIKHGD      
UKW-B YRUHQSLDPXNGOKMIEBFZCWVJAT      
UKW-C FVPJIAOYEDRZXWGCTKUQSBNMHL      

 
Norway Enigma
In 1945, immediately after WWII, some captured Enigma-I machines were used by the the former Norwegian Police Security Service: Overvaakingspolitiet. They modified the wheel wiring and the wiring of the Umkehrwalze (UKW, reflector). The wiring of the Eintrittzwalze (ETW, entry wheel) and the position of the turnover notches on the wheels were left unaltered. A machine that is modified in this way, is often called Norway Enigma or Norenigma as suggested by Frode Weierud in 2001 in order to discriminate between the standard and the modified wiring [2].
 
Wheel ABCDEFGHIJKLMNOPQRSTUVWXYZ Notch Turnover #
ETW ABCDEFGHIJKLMNOPQRSTUVWXYZ      
I WTOKASUYVRBXJHQCPZEFMDINLG Y Q 1
II GJLPUBSWEMCTQVHXAOFZDRKYNI M E 1
III JWFMHNBPUSDYTIXVZGRQLAOEKC D V 1
IV ESOVPZJAYQUIRHXLNFTGKDCMWB R J 1
V HEJXQOTZBVFDASCILWPGYNMURK H Z 1
UKW MOWJYPUXNDSRAIBFVLKZGQCHET      

 
References
  1. Philip Marks and Frode Weierud,
    Recovering the Wiring of Enigma's Umkehrwalze A

    Cryptologia, January 2000, Volume XXIV, Number 1, pp. 55-66.

  2. David Hamer and Frode Weierud, 2001, personal correspondence.

Further information

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