(three-wheeled Service machine only)

Steckered Enigma machine adopted by the German army. Wheels used: Umkehrwalze A (reflector) and wheels I, II, III. Messages used a fixed daily Grundstellung to double encipher each message key. The message header would contain two trigrams which is the double enciphered message key enciphered using the daily Grundstellung (message key was keyed in twice).

Late 1932 Polish Cryptanalyst Marian Rejewski recovers the entire machine wiring by mathematical analysis using a group of intercepts and machine settings for two months, September and October 1932, supplied by the French.

On 2nd November Umkehrwalze B was introduced, replacing Umkehrwalze A and this remained in use until the end of the war in 1945.

On September 15th the fixed daily Grundstellung was dropped. Each message must now have a different Grundstellung selected by the operator. The message header would contain three trigrams, the Grundstellung followed by the double enciphered message key enciphered using the message Grundstellung.

On 15th December wheels IV and V were added. Three wheels could now be selected from a set of five — giving 60 possible arrangements. A different wheel arrangement could now be used for every day of the month. The two additional wheel wirings were quickly recovered by Rejewski.

On 1st January the number of plugboard connections was increased from six to ten.

The First Welchman-Turing Bombe enters service in March.

On 1st May the double enciphered message key was dropped. The Message key was only enciphered once from now on. The message header would contain two trigrams, the message Grundstellung followed by the enciphered message key.

Sample Message
A sample test message using the 1940 procedure:

Wheel Order II I IV (2 1 4) Ringstellung CAS Steckers AG CH EP JX LZ NR OQ SV TW UY Selected Grundstellung SCA Message key enciphered at this Grundstellung ZHR Message: 1645 - 40 - SCA ZHR - MKINZ FZBWZ FEGRJ CPSAR BHCGB EQJFH AJIPV OMEZL ar sk

(Set up the machine as above, Set the wheels to SCA. Type in ZHR. Note which three lamps light up. Set these three lamp letters on the wheels and type in the 40 letter message).

Message length
Message lengths were strictly limited to a maximum of 250 letters, or fifty groups of five - there were only fifty cipher group boxes on the pre-printed message forms. Messages longer than 250 letters were split into two or more parts. Something like this may be used:

0824 - 2tle - 1tl - 244 - PGS YJZ - UPXBW BDFUD LBNXZ XAZQA ....... 0824 - 2tl - 233 - JDR IGU AMXNL TONVD GDLSV WKOLD .....

This is a two part (2 teile) message composed of part 1 (1 teil) of 244 letters and part 2 (2 teil) of 233 letters. The time of origin of the message is 0824 hours.

There were many variations to the Enigma procedures in the Army, Air Force and Navy. Air Force (Luftwaffe) messages usually included a message number in the message header. Most networks also used a Kenngruppe. This was a three or more letter indication used to identify a cipher network and hence tell the receiver which key-sheet was used to encipher the message. The Kenngruppe usually consisted of three letters taken from a list of daily settings, four for each day. These three letters were arranged in random order and preceeded by two dummy letters. This group of five, sent in clear, would form the first group of the message. Another variation was to include the group of three letters with the message indicator. The Kenngruppe was later dropped from some networks, since it gave away information about the networks and identified messages on the same key.
Naval Enigma used an entirely different procedure.

Sample message forms illustrating an original message from July 1941

German Enigma operator's
message form.
Reconstructed Intercept Operator's
message form.

All rights to the material described on these pages belong to
Geoff Sullivan & Frode Weierud, © March 2006

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