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Rotor Enigma K
Railway variant of Enigma K (A27)
- wanted item
During WWII, the Germans used a special Enigma machine for
the German Railway (Reichsbahn).
It was basically a standard Enigma K with rewired wheels
and a rewired UKW. Furthermore, the position of the turnover notches
of wheels I and III were swapped [1].
Enigma traffic from the German Reichsbahn was first encountered
by the codebreakers at Bletchley Park
on 25 July 1940 and all messages
were decrypted until the traffic ceased a month later, on 27 August 1940.
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According to internal BP reports, Colonel Tiltman was responsible
for breaking Railway Enigma during this period.
Early in the next year, on 23 January 1941, railway traffic was intercepted
again, originating from Eastern Europe, Russia and the Balkans.
Two weeks later, on 7 February 1941, the traffic was broken for the first time.
BP named the railway traffic key Rocket, but later renamed it to Rocket I.
Although there are no known images of a Railway Enigma, it is most likely
that it was a standard Enigma K with rewired wheels and a rewired UKW.
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In his 'Report on E Operations of the GC&CS', US codebreaker
William Friedman
claimed that Railway Enigma had a moving UKW,
but this is highly unlikely [2].
First of all, as the machine only has one notch on each wheel, the
UKW would hardly ever step if it could move at all. Secondly, the only
machines known to have a movable UKW are the
Zählwerk Enigma and
Enigma G,
both of which have multiple turnover notches that cause frequent stepping
of the UKW. It is likely that Friedman meant that the UKW was settable,
which is the case with Enigma D
and Enigma K.
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After the first successful breaks in 1941, the railway traffic key was
named Rocket. It was mainly used on railway traffic networks in Eastern
Europe, Russia and the Balkans. It was later renamed to Rocket I in
order to discriminate it from other railway networks.
Breaking Rocket I was relatively easy for BP, and the network provided
good intelligence about production and movement of supplies.
Nevertheless, problems with Rocket I were reported on 19 September 1944,
and it wasn't before 28 October that BP gained entry into the traffic again.
The blackout was apparently caused by eccentricities in the cribs
during this period [1].
The problems with Rocket I illustrate that even a standard Enigma K,
without the Army's plugboard (Steckerbrett) could be hard to break if
the contents of the messages were less predictable. It also shows that the
Bombes were virtually useless without good cribs.
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In September 1942, a similar key appeared for Western Europe. The new
key was called Rocket II and was only broken once when it was using
the Rocket I machines. Apparently, the traffic consisted of practicing
messages only. Judging from the characteristics of these messages, the
(practicing) traffic continued until May 1944, after which a new key,
and possible another machine, was introduced. They new key was called
Rocket III and remained unbroken for quite some time.
For a long time it was unclear whether Enigma was used at all.
After capturing some key sheets in August 1944, some of the older
messages were decrypted. It became clear that Enigma was used, but
that the contents of these messages were sufficiently 'obscure'
so that cribs could not be used easily.
It is most likely that Rocket II and III used the (military)
Service Enigma (Enigma I).
Rocket II was later renamed to Blunderbuss.
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The table below shows the wiring for the standard Railway Enigma
(Rocket I). Only wheels I, II and III were used. Note that the turnover
notches are the same as on commercial Enigma K,
but that the position of the notches of wheels I and III
appear to have been swapped. 1
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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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JGDQOXUSCAMIFRVTPNEWKBLZYH
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V
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N
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1
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II
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NTZPSFBOKMWRCJDIVLAEYUXHGQ
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M
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E
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1
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III
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JVIUBHTCDYAKEQZPOSGXNRMWFL
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G
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Y
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1
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UKW
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QYHOGNECVPUZTFDJAXWMKISRBL
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In reality , the position of the notches of wheels I and III were not
swapped, but were misinterpreted by BP. See the note below for further
information.
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Please note that these wiring details, are as they were
recovered cryptanalytically by the codebreakers at
Bletchley Park (BP). This is not the original (physical)
wiring used by the Germans.
They are equivalent however, provided that appropriate adjustments are made
to the ring settings for a given daily key.
In the same vein, the turnover positions of wheels I and III are swapped as
result of a misidentification by BP, rather than a physical swapping of
the alphabet rings by the Germans.
BP was aware of both differences, at least by 1944,
and knew which corrections were needed. Full details were given
by Philip Marks in Cryptologia of 2015/1 [3].
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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.
- William Friedman, Report on E Operations of the GC&CS at Bletchley Park
Signal Security Agency, Washington. 12 August 1943. pp. 39, 67.
NARA, RG 457, NSA Historical Collection, Box 1126, Nr. 3620. 1
- Philip Marks, Enigma Wiring Data: Interpreting Allied Conventions from WWII
Cryptologia Volume 39, 2015, Issue 1.
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Declassified by NARA on 6 June 2003.
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© Crypto Museum. Created: Saturday 18 September 2010. Last changed: Sunday, 09 October 2022 - 13:43 CET.
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