- wanted item
Schlüsselgerät 41 (cipher machine 41), or SG-41, was a mechanical pin-wheel
cipher machine that was developed during WWII
by Regierungsoberinspektor Fritz Menzer as a replacement candidate
for the (Abwehr) Enigma-G machine
. It was manufactured by Wanderer Werke
in Chemnitz (Germany) and was introduced on 12 October 1944.
Although 11,000 units were ordered, only between 1000 and 2000 units
had actually been delivered by the end of the war.
The machine is also known as Hitlermühle (Hitler Mill) because of
the large crank at the right.
The machine is not based on the rather common principle of the rotor machine,
like the Enigma,
but merely on the pin-and-lug principle of the C-machines,
made by Boris Hagelin in Sweden.
Similar systems were developed by Hagelin before the war
(e.g. the C-38)
and were used during the war by the American Army
Although the SG-41 is clearly based on the
C-38/M-209, it has been improved
in a number of areas. In particular, it features very irregular wheel
movements, plus wheel stepping in both directions, making it very difficult
to break .
The image on the right shows a typical SG-41 machine that is in the
collection of GCHQ.
The machine shown here is the alphanumerical
variant with 26 letters on the keyboard (A-Z). The letter J
is marked in red, probably as it is used to shift between letters and
When in storage, the machine is normally protected against dust
and damage by a rectangular cover.
According to the identification shield
that is mounted at the rear,
the machine shown here has serial number 000460 and was manufactured
in 1944 by Wanderer-Werke AG (manufacturer code CXO) in Siegmar-Schönau .
At the time, Wanderer was one of the leading manufacturers of typewriters
At the outbreak of the war, Siegmar-Schönau was a large industrial city
in eastern part of Germany. Today, the former city is a suburb of Chemnitz (Germany).
The exterior of the SG-41 is quite different from the
(or actually the BC-machines) on which it is clearly based. The case is
higher than that of the Hagelin BC-38
and it features a large paper storage compartment at the bottom
which is accessible from the front.
The machine is not driven by a motor but is hand-operated with the foldable
crank at the right. At the front left of the top surface is a character
counter that can be reset with a large knob to its right.
Below a rectangular cover at the top are the
that can be released (i.e. unlocked) with a lever at the right.
Once unlocked, the initial position of the wheels can be set.
The leftmost four wheels have letters on them, whilst the the remaining
two are marked with numbers. In order to maximise the cipher period of
the machine (i.e. the number of steps before it repeats itself), the
number of steps is different for each wheel.
At present, the exact number of steps on each wheel is unknownto us,
but from the image above we can deduce that wheel 4 probably has 23 steps
(A thru X, the 'J' is not used) and wheel 5 has 24 steps.
Also note that the numbering on the rightmost wheel is not contiguous
(...27 30 32 35 37...).
The SG-41 was also available in a numbers-only variant,
which is shown in the image on the right. The outer dimensions of
the machine are identical to the 'full' version, but the keyboard
has only 10 keys that are divided over two rows.
The mechanism of the machine is nearly identical to the
mechanism of a Hagelin C-38
or the American M-209.
At the rear is a rotating cage
with a number of bars with
tabs on them. Unlike the M-209 however, the tabs on the
bars of the SG-41 are not movable, just like on the
and C-37 models.
The SG-41 was first encountered by the codebreakers of
at Bletchley Park
on 12 October 1944. According to former codebreaker
they knew that the machine had six cipher wheels that moved irregularly,
sometimes even backwards. Even when the pure key was available to them,
they were not able to reconstruct the wheel settings and the pin patterns.
Such advanced features were not available on the Hagelin machines
until much later with the CX-52.
managed to read a few messages in depth, they were
not able to solve the machine during the war. The machine remained a
complete mystery to them.
According to Batey, a post-war US Signal Security Report
described it as a 'remarkable machine' .
The machine was designed by Regierungsoberinspektor Fritz Menzer,
who had caused the intelligence sections
and ISOS at Bletchley Park
problems before, with the introduction of numerous reforms and improvements
to the Abwehr's ciphers. The SG-41 was intended to replace the
that was used for the Abwehr's European communication, but by the time
the war was over, it was only in use on some internal networks.
Had it been implemented on a large scale, as intended, it would
have posed a real problem for the Allied codebreakers.
Below is a short film from the
about the preservation of an SG-41 that was found
at the bottom of a lake. Although it is not possible to restore this
machine to its former glory, it is important that it is protected against
further deterioration. In the film, curator Dr. Carola Dahlke explains
the problems of toxic fumes that are emitted by the Nitrocellulose keys.
The toxic gasses may cause deterioration of the keys themselves, but also
of the remains of the machine, and potentially also of any other objects in its
vicinity. Until a proper solution is found, the machine will therefore be
stored under controlled conditions when it is not on public display.
- GCHQ, Photographs of two SG-41 units from the collection of GCHQ
Photographs kindly supplied by GCHQ.
3 December 2012. Crown Copyright.
- Mavis Batey, Dilly, The Man Who Broke Enigmas
2009. Hard cover, ISBN 978-1-906447-01-4.
- Wikipedia, Schlüsselgerät 41
German. Retrieved January 2014.
- Oberkommando des Heeres,
Liste der Fertigungskennzeichen für Waffen, Munition und Gerät
Reichsdrückerei Berlin 1944, reprinted by Pawlas, Nürnberg, 1977.
- Wikipedia, Siegmar-Schönau
German. Retrieved January 2914.
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© Crypto Museum. Created: Sunday 19 January 2014. Last changed: Monday, 03 September 2018 - 14:25 CET.