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Rotor Enigma G
A rare version of Zählwerk Enigma G31
By Paul Reuvers & Marc Simons — 7 July 2007
Enigma G111 is an Enigma cipher machine model G31, also known as
a Zählwerksmaschine (counter machine) or Enigma G, manufactured
in 1931 by Chiffriermaschinen AG (ChiMaAG)
in Berlin (Germany) and sold to the Hungarian Army.
It is a rare variant of the Enigma G with a 28-pin socket
for connection of a printing device, and is known by the internal designator
Ch.15b.
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In May 2009, this machine, with serial number G111, turned up at
auction house Hermann Historica in München (Germany).
It was scheduled for auction in October 2009, but was not in the best
condition. Prior to the auction, on 1 July 2009, Crypto Museum was
allowed to investigate the machine and take detailed photographs.
The machine is different from the
regular version of the Enigma G31 (Ch.15a),
in that it has a connector at its left side, which is not present on other
versions. It allows the larger Enigma H29 to be used as a
printing device for Enigma G31.
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To the best of our knowledge, this is the first time that this version of
the Enigma G is investigated and described.
Our findings are presented here, and in
more detail in our paper G111: A rare version of Zählwerk Enigma G31,
which can be downloaded here [A].
Thanks go to Mr. Thomas Rief of auction house Hermann Historica for
providing access to the machine, and to Enigma historian Frode Weierud
for his invaluable advice, research and background information [6].
➤ Download the full paper
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UPDATE 10 December 2025 —
At the auction in October 2009, the G111 was not sold — the reserve
price wasn't met — and the machine was subsequently returned to the owner.
In February 2018 we received a letter from the owner, to inform us
that he had meanwhile restored the machine to operational condition.
This page, as well as our paper about the G111, have now been updated
to reflect the restoration and correct a few mistakes.
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Differences with regular Enigma G
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Compared to other surviving machines,
the G111 has the following differences:
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The case of the G111 is nearly identical to the case of the
standard Enigma G31. It measures 250 × 270 × 165 mm.
The only difference with the standard case is the presence of a
large hole at the left side.
Behind this hole is a 28-pin socket that could be used for connection
of an external printing device.
In practice, the large printing Enigma H was used as
a printer for the G111.
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One of the differences of the G111 is the
curved text label above the power selector
at the top right of the machine's upper panel.
On a regular Enigma G (Ch.15a), this switch has four positions:
hell (bright), dkl (dunkel, dark), aus (off) and Sammler
(accumulator). It is shown in leftmost drawing below, with the knob set
to hell (bright).
The rightmost setting (Sammler) is for connection
of an external power source, such as a vehicle battery or a mains
power supply unit.
On the G111 (Ch.15b), this knob also has four positions, but the rightmost
setting is marked Gr. Masch. (large machine). It is shown in the middle drawing
below. When the machine is connected to a printing device (Enigma H29),
the power selector must be in this position. At the same time, the two
power terminals – located in front of the power selector – must be shorted
by means of a short wire. This is mandatory, as otherwise the circuit
is broken and the printer won't print.
The rightmost drawing above, shows the electrical symbol of the power
selector, as it is used in the circuit diagram.
It is a 4-position rotary selector of which the master contact
pivots on a central axle. In each position is connects one of the four
contacts at the lower half to the diagonally opposite contact at the
upper half. The selector is shown here in the rightmost position.
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The table below shows the wiring of the rotors of the G111,
the entry disc (Eintrittswalze, ETW) and the
reflector (Umkehrwalze, UKW). The column 'Turnover'
shows which letter is visible in the window when the rotor
causes a turnover of the rotor to its left on the next key-press.
Note that these positions are different from the
actual positions of the notches on the circumference of the rotor
(given in the column 'Notches').
Only rotors I, II and V were
found with this machine.
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| Rotor | ABCDEFGHIJKLMNOPQRSTUVWXYZ | Notch | Turnover | # | |
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| ETW | QWERTZUIOASDFGHJKPYXCVBNML | | | - | 1 |
| I | WLRHBQUNDKJCZSEXOTMAGYFPVI | ACDEHIJKMNOQSTWXY | SUVWZABCEFGIKLOPQ | 17 | |
| II | TFJQAZWMHLCUIXRDYGOEVBNSKP | ABDGHIKLNOPSUVY | STVYZACDFGHKMNQ | 15 | |
| III | ? | CEFIMNPSUVZ | UWXAEFHKMNR | 11 | |
| IV | ? | ? | ? | ? | |
| V | QTPIXWVDFRMUSLJOHCANEZKYBG | AEHNPUY | SWZFHMQ | 7 | |
| UKW | IMETCGFRAYSQBZXWLHKDVUPOJN | | | - | 1 |
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➤ Other Enigma G wirings
As becomes clear from the above table, the number of notches as well as the
turnover positions of rotors I
and II are identical to those on the same rotors of other Zählwerk machines
(17 and 15 notches respectively). We therefore assume that rotor III had
11 notches that are at the same positions (here shown in red) as on rotor III
of other surviving Enigma G machines.
So far, rotor IV hasn't been found, so we don't know the number and positions
of the notches on that rotor, but from the series it seems likely that it had
9 notches.
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A unique feature of this particular Zählwerk Enigma, is the
presence of a socket at the left side,
close to the UKW.
So far, this feature has not been found on any other Zählwerk Enigma before. 1
The expansion is described in patents DE536556 [3]
and DE595075 [4].
It allows another – much larger – printing Enigma (such as the Enigma H29)
to be connected and used as a printing device.
It is believed that the printer connection was an option that was also
available for the Enigma I.
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When used in this way, the Enigma H (shown in the picture on the
right) would only function as a printing machine; its cipher capabilities
were disabled. Connecting a printer allowed a cipher clerk to decipher
incoming messages much faster than when reading-off the lamps and
writing down the letters. He could not use the Enigma H
directly, as it is not compatible with the
Zählwerk Enigma or the military Enigma I.
On the G-111, the socket for connecting the Enigma H,
is located at the lower left side of the machine.
A hole of approx. 50 mm is present in the lower part of the metal body.
It gives access to the socket which is mounted behind the hole.
The hole can be covered with a metal flap.
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When the machine is mounted inside the wooden transit case,
a circular hole in the side of the case provides access to the socket.
The socket is actually mounted slightly off-centre,
but the hole in the metal body is large enough to accommodate the plug.
To the right of the socket is an oddly-shaped metal flap that pivots
around an M5 bolt. It can be used to cover the socket and protect
its contacts when it is not in use.
The flap has two small folded edges that allow it to be moved with,
say, a finger nail. The upper edge reaches just above the lower part
of the wooden case, so that the flap can be lifted even when the
machine is mounted inside the wooden case.
The illustration above shows how the flap can be moved.
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The relic of Enigma G-110 has meanwhile been unearthed from a battlefield
and is now on public display at the Bletchley Park Museum. It is not
in operational condition and has no rotors.
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The Zählwerk Enigma has 26 lamps on its lamp panel.
These lamps are specified at 3.5 V or lower and are normally powered
by a 4.5V battery. The current trough the lamps is approx. 200 mA.
When the printing device is attached however, the voltages and currents
are much higher, as the machine has to drive the solenoids inside
the Enigma H directly. This would blow the lamps.
Removing the lamps was not considered an option, as one had to remove
them each time the printer was attached,
and re-install them for standard operation without a printer.
To overcome this problem, a solution was developed, in which all 26 lamps
are automatically disabled as soon as the printer cable is plugged in.
This solution is described in
patent DE595075 [4].
The patent describes a switch that is operated by the plug.
The cable from the printing device has a plug with 28 spring-loaded contacts.
After inserting it into the socket, it must be turned slightly
to lock it in place.
When doing so, the spring-loaded contacts of the plug slide into position to make
contact with the circular pads of the socket.
At the same time, an internal cylindrical connector behind the socket is
moved out of position, which interrupts the wiring to the 26 lamps.
The switch is a complex construction that consists of static and movable
parts, both inside and outside the machine. The image above shows the static
part of the socket.
The plug (not part of the machine) actually behaves as part
of the switch. It has 28 spring-loaded contacts, arranged in a zig-zag pattern,
that matches the contact pads of the socket.
At the center is a key that fits the asymmetric key-hole at the centre
of the socket. It can only be inserted one way around.
The exploded view below clarifies the operation of the socket/switch.
Please note that during our investigation, we were unable to dismount
the switch assembly. We are therefore uncertain about the shape
of the centre part and the cylindrical contacts.
For the drawings below, we made some 'educated guesses', based on
the German craftmanship of the era. This is also the case for the cable part
(i.e. the plug) which we have never seen (yet).
The socket assembly consists of a package of three pieces of Pertinax (Paxolin).
The leftmost one is square, and is visible from the outside.
The other parts are disc-shaped in order to fit through the
circular hole in the left side of the die-cast chassis.
The centre part (i.e. the first disc-shaped unit) is smaller,
to accommodate the wiring to the Enigma keyboard.
The three parts are held together with 4 recessed M3 screws,
fitted from the rear (assembly mounting screws).
This switch assembly is inserted from the left into the
circular hole in the chassis
(below the UKW) and is mounted to the chassis with three
recessed M4 screws.
The drawing below shows a cross section of the assembly,
the die-cast chassis and the rotatable switch, as seen from the top.
When no plug is inserted, the spring-loaded contacts of the rotatable switch
are aligned with the contact pads of the assembly. In this situation,
the lamps are connected to the corresponding switches of the keyboard.
When inserting the plug, the spring-loaded pins of the plug are not
aligned with the contact pads of the assembly, as they are displaced by
approx. 12.8°. The key, which is a fixed part of the plug, reaches through
the assembly into the rotatable switch.
Once the plug is fully pushed in, is is turned approx.
12.8° clockwise until the internal rotatable switch is locked
in its second position.
A spring-loaded bullet ensures that the switch is kept in this position.
The contacts of the plug – that were previously positioned in between
the contact pads – are now resting on the contact pads of the socket.
At the same time, the rotatable switch is moved out of position and
its contacts are now resting in between the contact pads.
In other words: when the plug is turned clockwise,
the wiring from the Enigma keyboard to the lamps is interrupted
and is instead connected to the socket and, hence, the external plug.
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The printer socket has 28 contacts, two of which are marked
(33) and (34). They carry the common rail (33) and the
keyboard-release signal (34) respectively. The remaining
26 contacts are for the letters (A-Z).
Below is the simplified circuit diagram of the machine (Ch.15b), in
which only the first four letters of the keyboard are shown.
Let's first consider normal operation (without printer).
The power selector (S1) in the the hell (bright) position.
The printer is not connected, so the large 26-pole switch (S2)
— integrated with the printer socket — is in the leftmost position.
Move the mouse over the drawing to see what happens when the letter
'Q' is pressed.
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Enigma G31 (Ch.11b) in normal configuration — Selector S1 set to 'hell'
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We will now connect the printer to the terminals at the top.
When inserting the plug into the printer socket at the left side
of the machine, the embedded switch (S2) is set to the rightmost position.
The lamps are now disconnected and the keyboard switches are now
connected to the printer instead. To use the printer, the power
selector (S1) must be set to 'Gr.Masch.' (large machine) and the
two power terminals (P) must be shorted with a strap wire to ensure
circuit continuity.
Move the mouse over the drawing to see what happens when the letter
'Q' is pressed.
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Enigma G31 (Ch.11b) in printer configuration
Selector S1 set to 'Gr.Masch.' and power terminals (P) shorted
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In this situation, the internal battery of the Enigma is disconnected,
whilst power is provided by the printer through pin (34) of the printer
socket. Note the extra switch (S3) that provides the keyboard-release
signal to pin (33) of the socket. In rest, when no key is pressed,
it is connected to pin (34). As soon as any letter on the keyboard is
pressed, this signal is interrupted.
S3 is mounted under the actuator below the keyboard.
It is not present on other Enigma G models.
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In February 2018 we received a letter from the owner of the G111, who
wishes to remain anonymous, along with detailed photographs and some
video footage of the restoration process. It was decided to leave
the original character and history of the machine intact, and not to
'over-restore' it. This means that no painting or nickel plating was done.
Damaged or missing parts were replaced by original era-correct
components whenever possible. This process took several years.
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The wooden case was completely taken apart, after which the individual
panels were restored by means of vacuum sizing. This stabilises
the wood while retaining the original patina. The case bottom,
whose wood had warped, was also repaired with this technique. The missing
part above the circular cutout at the left side, was recreated from
80+ year old oak wood with identical characteristics. It was coloured
to match the existing case.
The case was then reassembled.
The image on the right shows the left side of the restored case.
The repair is barely visible now.
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The rotors did initially not move when a key was pressed, as the machine
was somehow blocked or binding. After removing the outer shield, a lot
of dirt was found inside the machine, including mouse droppings, larvae,
matches, pieces of (news)paper and a stone. The stone appeared to be the
part that was blocking the machine. Once it was removed, the rotor stepping
mechanism worked again. No corrosion was found on the keyboard switches,
although they all had to be cleaned and readjusted. Some bolts that were
missing from the keyboard section were replaced.
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An extra switch was found in the area between the keyboard assembly
and the machine's base. This switch (S3) which is normally closed (n.c.),
is opened as soon as one of the keys is pressed.
It is wired to the large 28-pin printer connector.
All lamp and keyboard contacts were cleaned, but the wiring harness
– which is still in excellent condition – was left untouched.
After replacing the light bulbs with modern flat-head replicas,
everthing worked again, except for the 'U' lamp.
Tracing the wiring revealed that this is probably caused by a
broken wire in the wiring harness.
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Although this should be relatively easy to fix, it was decided
no to do so, as it involved taking the wiring harness apart at the
risk of damaging more wires. This means that in the present state
of the machine, 1 of the 26 lamps does not light up, but the wiring
harness is still fully original.
On the lamp panel, the letter 'V' (which had cracks)
was replaced with a newly created film fragment.
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The three rotors were found to be in excellent condition, and only had to
be cleaned. When the rotors are installed in the machine, their position
is normally retained by means of four red rubber pressure rollers at
the rear.
Three of these had cracks and the forth was completely missing.
All four rollers were replaced by equivalent parts.
The power selector, which is fitted on top of the battery compartment,
somehow got broken and was no longer functional. The upper part, which
pivots on a central axle, is rotated by the
knob that is fitted to the metal lid
of the machine. It allows selection between dkl (dunkel, dark),
hell (bright), aus (off) and Gr.Masch (large machine).
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Wooden case in bad condition Part of wooden case missing (above hole at left side) Vernier damaged/missing from top of case lid Several glass key caps missing/broken Wrong type of light bulbs Alphabet film on lamp panel damaged Red rubber pressure wheels worn out - Lamp U(7) does not light up (broken wire)
Power selector broken
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- Wooden case restored by means of vacuum sizing technique
- Missing part replaced with 80+ year old oak wood
- Lid retaining brackets replaced with originals
- Five glass key tops (1 mm) replaced
- Lamps replaced by modern reproductions
- Lamp film letter 'V' (only) replaced
- Power selector restored with era-correct Pertinax
- Machine ibterior thoroughly cleaned.
- All contacts cleaned and checked.
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Photographs of the restoration
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Below are some photographs of the restoration process of the
G111, which was carried out by its owner over the course of
several years. The owner, who wishes to remain anonymous,
invested a lot of time and money to find the original parts,
or appropriate alternatives or reproductions [7].
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This short video clip shows the restored G111 in operation.
The video was recorded in the dark, so that the glowlamps on the
lamp panel are clearly visible. To block ambient light, the case lid is
placed in 45° position, by placing the lid retaining brackets in
forward position.
Source:
Anonymous [7]
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This short video clip shows the same machine (G111) with its
lid open, whilst key are being pressed on the keyboard.
Note the irregular stepping of the rotors.
In this case, no battery is installed, so no lamps are lighting up.
Source:
Anonymous [7]
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Device Rotor-based cipher machine Purpose Civil and military message encryption Brand Enigma Type G Model G31 Designator Ch.15b Serial number G111 Manufacturer H&R Country Germany Year 1931 Customer Hungarian Army Rotors 3 of 5 (I, II, V) 1 Turnovers 17, 15, 7 Reflector Settable and driven, s/n G111 Wiring Special wiring Stepping Irregular (coupled gear) Plugboard no Extras Printer connector, crank, green sunlight filter (option) Dimensions 270 x 250 x 165 mm Weight 7.2 kg (9.4 kg with wooden case)
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Only rotors I, II and V are present. Rotors III and IV are missing.
The surviving rotors have matching serial numbers (G111).
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- G-111: A rare Zählwerk Enigma variant
Full details of the Enigma G-111 with high-resolution drawings.
Crypto Museum — Paul Reuvers and Marc Simons. August 2009.
Version 2.00, 10 December 2025.
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© Crypto Museum. Created: Tuesday 07 July 2009. Last changed: Sunday, 14 December 2025 - 14:33 CET.
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![The restored Enigma G31 (Ch.15b) with s/n G111 [7]](img/300604/129/full.jpg)
