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M16913/aye/44
- investigation
Enigma M16913 is a rotor-based Enigma cipher machine
Model M4, manufactured in 1944 by Olympia Büromaschinenwerke AG
in Erfurt (Germany).
The machine was used throughout in the final two years of World War II (WWI)
by the U-Boat division of the German Navy (Kriegsmarine).
It is a four-wheel version, that is also known by the manfucturer's internal
designator Ch. 11g4.
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The machine was found with naval wheels I, V and VIII,
Zusatswalze γ (extra wheel gamma) and Umkehrwalze B
(reflector B), all with matching serial numbers.
Especially the combination of Reflector B and extra wheel (γ) is
remarkable, as this combination was only used in April, August and December
of 1944, and March of 1945 [1].
If we assume that the machine was 'on active duty' right until the end of the war,
it seems likely that it was captured in Norway in March 1945,
as this is the last time the combination of UKW-B and Gamma was used
in an operational context [2].
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When the machine was rediscovered in The Netherlands in early 2022,
the metal cover over the wheel compartment was locked and the key was missing.
The lock was subsequently opened by a skilled lockpicker in April 2022, after
which the interior could be inspected. Judging from the state of the internal
parts (extremely dry and binding),
it seems likely that the machine had not been opened since WWII.
The machine is well preserved and shows mild traces of corrosion.
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The wooden case is in very good condition. The wood is dry and needs some
treatment, but is free from cracks.
The lock at the front is operational
and the carrying handle (grip) is a bit rusty,
which is not uncommon.
On the outside of the case,
below the metal carrying handle at the rear,
is the serial number M16913. The case lid can be removed for inspection
and/or operation.
Inside the top lid is a holder for 10
spare light bulbs. There are currently no spare light bulbs installed.
The rightmost bakelite holder for the spare patch cables is broken at the
upper fixation point, but this can be repaired easily and invisibly.
At the centre of the lid is a stamp that reads:
Kommando der Marine - Station der Ostsee
Druckschriftverwaltung
The stamp attributes this machine to the German Navy (Kommando der Marine).
The second part (Station der Ostsee) refers the German city of Kiel,
where the German Navy had its headquarters for units operating in the
Baltic Sea [2]. It is also the place where the German U-boats were built.
Below the stamp is a typed note that
is glued to the inside of the lid. It carries the machine's serial number
M16913. The note instructs the user to always set the leftmost cipher
wheel to 'A', in which case the machine was compatible with a three-wheel
naval Enigma machine (M1, M2, M3).
Inside the lower edge of the top lid is a metal plate with
the machine's serial number M16913.
The keyboard is complete and in good state. The posts are somewhat rusty,
but this is fixable. At the front edge is the
main serial number tag,
showing the German Navy order number (Na 220 900) and the full serial number
16913/aye/44. The state of the electric switches under the keyboard is
currently unknown. They will probably have to be reworked for proper operation.
The lamp panel is retained by two knurled bolts — one at each side.
It is in reasonable state, but some of the letters on the lamp
film are bulged-out somewhat. This is caused by the use of improper E10
lightbulbs, which might date back to the end of WWII when correct bulbs
were in short supply. Repair of the lamp film is not
possible as it is made of celluloid. Replacement seems unnecessary however.
The hinged front lid of the wooden case (Klappe) is held in place with two
metal hooks. It can be opened to give access to the
patch panel (Steckerbrett).
The stamp 'Klappe Schließen' is faintly visible on the inside of the flap.
11 patch cables are currently installed, one of which
is a spare and should actually be installed inside the top lid.
There are some issues with the Steckerbrett — some plugs are not held in
place — but further inspection is beyond the scope of this survey.
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The cover over the wheel compartment was locked and the key was missing.
It is likely that this cover had not been opened since the device was
confiscated at the end of the war. The lock has now been opened by
professional lockpicker Barry Wels, who created a
working key by means of impressioning,
a technique
for which neither the machine nor the lock had to be disassembled.
The rotor stack
was binding, due to mild corrosion and drying out of the
mechanism. Especially the reflector (UKW-B) could initially not be moved to the left, as a result of which the rotor stack was stuck in place. After
cleaning the short sub-axle at the left and treating it with penetrating oil,
it could eventually be moved out of the way, after which the rotor stack
could be taken out.
All axles have since been cleaned and treated with special oil,
so that all parts now move freely.
The machine's serial number is also
engraved in white in the bottom
panel, below the rotor stack.
The entry wheel (Eintrittswalze)
is made of black bakelite and is in excellent condition.
The battery compartment is clean and is free from corrosion and battery
chemicals.
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Inside the machine are cipher wheels I, V and VIII, all with the same
serial number as the machine (M16913}. The rotors are in very good shape,
except for
one of the Ringstellung locking arms
of rotor V, that was partially missing.
The missing part was later retrieved from the interior of the machine.
This issue is caused by metal fatigue of the die-cast arm, in combination
with local corrosion and swelling of the part. Small cracks in the die-cast
material are visible.
It is unknown whether replacement parts exist.
Luckily, this issue does not affect the operation of the machine.
Reflector B (UKW-B) is removable and is made
of black bakelite. It carries the machine's serial number (M16913).
It is used here with Extra Wheel (Zusatzwalze) γ (gamma), which also
has the same serial number as the machine (M16913). Both wheels are in
excellent condition.
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During WWII, the German Navy used 3-rotor machines (M1, M2 and M3),
which were compatible with the Enigma I of the Army (Heer) and Air Force
(Luftwaffe). On 2 February 1942, a 4-rotor Enigma machine (M4) was introduced,
which was exclusively used by the U-Boat division and very few others.
Most other division (e.g. the weather service) continued to use the 3-rotor machines. A 4-rotor machine can be made backwards compatible with a 3-rotor
machine, by placing the leftmost wheel (Zusatzwalze) in the A-position. 1
In this position, an M4 behaves like an M3.
As with most surviving Enigma M4 machines it is difficult to trace the
history of the M16913.
As far as we know, there are no surviving documents with details
about this specific machine. Based on observations however, it is possible to
draw conclusions and make a few educated guesses.
It is certain that the machine was manufactured in 1944 by
Olympia Büromaschinenwerke AG in Erfurt (Germany). At that point in time,
the older 3-wheel naval Enigma machines (M1, M2 and M3) were no longer in
production, which means that M4 machines were not only supplied to the
U-Boat division, but also to other parts of the German Navy. In the latter case,
the M4 machine was used in M3-compatible mode by setting the leftmost wheel to
position 'A'.
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Assuming that the Zusatzwalze and UKW are a matched pair (i.e.
B+β or C+γ) and that the ringstelling of the
Zusatzwalze is a the letter 'A'.
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The initial user of the machine is identified by a stamp at the centre of the
inside of the top lid:
Kommando der Marine - Station der Ostsee
Druckschriftverwaltung
This means that the machine was issued in 1944 to the
Druckschriftverwaltung (printing service) of the
German Navy, located in Kiel (Germany). This department was responsible for
all printed material used by the Navy, including operating instructions,
codebooks and key lists, for which the M4 was sometimes used in
M3-compatible mode (depending on who the contacted party was), subject to the
current key sheet.
This is indicated by a typed note inside the top lid:
Geheim
Merkblatt zum Schlüssel M
Form M4 - Prüfnummer M: 16913
Bei der Handhabung dieses Schlüssels M ist besonders wichtig:
Ist die Grundstellung eine dreistellige Buchstabengruppe, so ist
folgendes zu beachten:
a) Die Grundstellung und der Spruchslüssel werden in dem zweiten,
dritten und vierten Fenster von links eingestellt.
b) Beim Einstellen der Grundstellung und des Spruchschlüssels so-
wie beim Schlüsseln muß im linken (ersten) Fenster immer der
Buchstabe A (rote Schrift) eingestellt sein.
c) Die Schlüsselung muß vollstandig wiederholt werden, wenn während
der Schlüsselung festgestellt wird, daß ein anderer als der
Buchstabe A im linken Fenster eingestellt ist.
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Secret
Leaflet for Key M
Form M4 - Check number M: 16913
Important when handling this Key M:
When the Basic Setting is a 3-letter group, the following should be noted:
a) The Basic Setting and the Message Key should be set in the
second, third and forth window from the left.
b) When entering the Basic Setting and the Message Key, as well as
when enciphering, the letter A must be visible in the leftmost
window (red) at all times.
c) The entire message must be repeated, when during encipering it is
noticed that a letter other than the A has been set in the leftmost window.
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As the printing service had to communicate with all parts of the German Navy,
it is likely that the machine was used in both M3- and M4-compatible mode,
in other words: that it was used as a 3-rotor and as a 4-rotor machine,
depending on who the contacted party was. If the keylist for that party
specified a 3-letter basic key (and message key), the machine was used
in M3-compatible mode and the leftmost wheel had to remain at 'A'.
If the keylist specified a 4-letter basic key, the machine was used as
a full M4 and all four wheel had to be set.
When the machine was recovered in early 2022, the upper lid was locked
and the key was missing. After the lock was opened by a skilled lockpicker,
it was noted that all rotors were binding on the shaft, which suggests that
it was left in that state at the end of the war. Furthermore, it was
found with UKW B and Zusatzwalze γ installed. In this state
it is not compatible with a 3-rotor machine. 1 This suggests that at the time
the M16913 was abandonned it was in use as a 4-rotor machine.
If we assume that the machine was 'on active duty' right until the end of
the war, it seems likely that it was abandonned in March 1945,
as this is the last time the combination of UKW-B and Gamma was used
in an operational context.
➤ More about the mixed use of UKW and Zusatzwalze
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Thin UKW B in combination with Zusatzwalze β (set to 'A')
is compatible with regular UKW B. Likewise, thin UKW C in
combination with Zusatzwalze γ (set to 'A') is compatible with
regular UKW C. The combination found here (UKW B and Zusatzwalze
γ) does not have a regular equivalent.
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Machine Enigma Model M4 Designator Ch. 11g4 Order No. Na 220 900 S/N M16913/aye/44 Year 1944 Manufacturer Olympia Büromaschinenwerke AG (Erfurt, Germany) User(s) Naval printing service and (probably) U-Boat division Wheels I, V, VIII Extra wheel γ (gamma) Reflector B
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- Wooden case superficially cleaned; dust removed
- Hinge of top lid cleaned and oiled
- Lock opened by professional lockpicker
- Two working keys produced without damaging machine and/or lock
- Device exterior superficially cleaned
- Wrong format light bulbs removed and scrapped
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- One Ringstellung-clip of Wheel V broken (does not affect operation)
- Several sockets on the plugboard must be reworked
- 4 light bulbs missing from lamp panel
- All 10 spare light bulbs missing
- Lamp film bulged out at several locations, due to use of wrong light bulbs
- Rightmost spare cable holder upper fixation point broken
- Keyboard switches need cleaning
- One large bolt missing from case bottom (is very common)
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- Detailed description of Enigma M4
- Enigma M4 wheel wiring
- Enigma family tree
- Other Enigma models
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© Crypto Museum. Created: Thursday 14 April 2022. Last changed: Friday, 01 July 2022 - 14:41 CET.
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