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G219
Enigma G31 used by the Dutch Navy

Enigma G219 is an Enigma cipher machine model G31 — also known as a counter machine — manufactured in 1938/39 by Heimsoeth und Rinke (H&R) in Berlin (Germany) for the Dutch Navy. In total, the Dutch Navy had at least 93 counter Enigma machines of the models G31 (Ch.15a) and the interoperable A28 (Ch.15). They were the largest Enigma G customer outside Germany [1].

The G219 was part of a batch of at least 27 Enigma G machines sold to the Dutch Navy in 1938 or 1939, just before the outbreak of World War II. It was supplied by N.V. voorheen Ruhaak & Co. in The Hague — the Dutch representative of ChiMaAG and Heimsoeth und Rinke (H&R). 1

The machine was found without its wooden transit case, as shown in the image on the right. At the right is a makeshift hole for a power cable. It was probably added by the Dutch Navy in the 1950s or 60s, as more devices with this type of hole have been found in Dutch museums.
  
Enigma G outside the wooden transit case

Inside the machine, the battery compartment is missing. It was probably removed at some stage after the batteries had been leaking. Although it is our intention to reproduce the battery box, it isn't a game breaker, as the machine can be used without it. All three cipher rotors (I, II and III) and the reflector (UKW) are present and have the same serial number as the machine. When the machine was found, it was partially dismantled and some of the screws were missing from the outer case shell. The machine has meanwhile been restored, and is fully operational again.

  1. When the G31 was introduced in 1931, the name of the company was Chiffriermaschinen AG (ChiMaAG). It was succeeded in 1934 by Heimsoeth und Rinke (H&R). As the G219 was supplied in 1938 or 1939, H&R was the manufacturer.

Enigma G seen from the left
Enigma G outside the wooden transit case
G219 without wooden transit case
Enigma G seen from the side
Rear view
Enigma G with open lid
Top view of the G31 (G219)
Top view of the G31 with open lid
Enigma G interior
Rotor set - right angle view
Rotor set - left angle view
Rotor set - front view
Rotors and spindle
Rotors and spindle - showing contact pin side
Contact pin (left) and contact plate (right) side
Enigma G interior (battery compartment removed)
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Enigma G seen from the left
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Enigma G outside the wooden transit case
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G219 without wooden transit case
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Enigma G seen from the side
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Rear view
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Enigma G with open lid
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Top view of the G31 (G219)
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Top view of the G31 with open lid
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Enigma G interior
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Rotor set - right angle view
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Rotor set - left angle view
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Rotor set - front view
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Rotors and spindle
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Rotors and spindle - showing contact pin side
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Contact pin (left) and contact plate (right) side
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Enigma G interior (battery compartment removed)

History
The Dutch Navy purchased the first six counter machines — Enigma model A28 — in 1928 [1]. These machines had the same size as a 'regular' Enigma and the rotors were of 'normal' size. In 1931, shortly after ChiMaAG introduced the Enigma G31, the Dutch Navy ordered one of the new smaller machines, G 128, probably for evaluation and for testing the compatibility with the A28.

World War II
It was not until 1938 however, that more Enigma G machines were ordered. Divided over several orders, the Dutch Navy purchased at least 81 Enigma G machines between 1938 and 1940. The last 6 machines arrived on 9 May 1940, one day before the German invasion of The Netherlands. It is likely that these 6 machines (and possibly others as well) were subsequently confiscated by the Germans.

During the war, the Dutch Navy operated from the UK, and the Enigma G machines were used aboard ships and submarines. After the sinking of two submarines — O-13 in June 1940 and O-22 in November 1940 — they were no longer used aboard submarines and were redistributed to other Dutch Naval units operating in British waters [1]. It is likely that G219 was part of it.

Post-war use
After the war, the Dutch Navy reused the surviving Enigma G machines, as becomes evident from the maintenance booklet of another Enigma G of the Dutch Navy, with serial number G221 [3]. 1 The machines were used aboard ships for communication with the Dutch Antilles and the Dutch East Indies. According to this booklet, the machines were used until at least 1955, after which they were replaced by modern equipment. They were retained as spare units until the mid-1960s.

In the mid-1970s, the Dutch Navy ordered all remaining Enigma G machines to be destroyed and discarded [2]. A few units escaped demolition and ended up in the collections of the Dutch Naval Museum (MDH) and the Dutch intelligence service BVD (later: AIVD). It is unknown how and why the G219 survived, but it is likely that it was given as a farewell present to a Naval officer on his retirement. After his death, it eventually became part of the Crypto Museum Collection.

  1. The G221 is currently held in the internal collection of the Dutch General Intelligence Service (AIVD).

Rotor set - front view

Wiring
Standard wiring
The G219 was supplied to the Dutch Navy with the standard commerial wiring of the rotors and the UKW. For a long time, it was assumed that the Dutch Navy had rewired the wheels before using the machines in an operational context, but evidence suggests that this was not the case.

So far, all Zählwerk Enigma machines (A28 and G31) that were used by the Dutch Navy had the standard commercial wiring when they surfaced in the post-war era. This means that the Dutch Navy could have been an easy target for US and British codebreakers, both during and after WWII. It also means that they might have been a target of the German codebreakers during the war.

Wheel ABCDEFGHIJKLMNOPQRSTUVWXYZ Notch Turnover #
ETW QWERTZUIOASDFGHJKPYXCVBNML      
I LPGSZMHAEOQKVXRFYBUTNICJDW ACDEHIJKMNOQSTWXY SUVWZABCEFGIKLOPQ 17
II SLVGBTFXJQOHEWIRZYAMKPCNDU ABDGHIKLNOPSUVY STVYZACDFGHKMNQ 15
III CJGDPSHKTURAWZXFMYNQOBVLIE CEFIMNPSUVZ UWXAEFHKMNR 11
UKW IMETCGFRAYSQBZXWLHKDVUPOJN      

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Interior
Below is a series of photographs that were taken during and after the restoration of the machine. Considering its age, the G219 is in a remarkably good condition. The die-cast bottom panel is complete and has not been 'eaten' by moisture or chemicals. Apart from the missing battery compartment and the lamp panel hold-down nuts, the chassis is complete and all wiring is intact.

The image above shows the machine as seen from the left rear side. It gives a clear view of the rotors and the stepping mechanism. Note the large empty hole in the side of the chassis, just below the rotors. In the Ch.15b version of the machine, this hole held a 28 contact socket/switch which could be used for the connection of a printing device. On the Ch.15a (shown here), this socket/switch is omitted. For a detailed description of this socket/switch, refer to our G111 page.

Enigma G interior (battery compartment removed)
Enigma G interior seen from the rear right
Interior seen from the rear left
Interior seen from the front left
Interior - seen from the front
Interior - seen from the rear
Interior - seen from the right
Interior - seen from the left
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Enigma G interior (battery compartment removed)
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Enigma G interior seen from the rear right
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Interior seen from the rear left
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Interior seen from the front left
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Interior - seen from the front
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Interior - seen from the rear
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Interior - seen from the right
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Interior - seen from the left

Restoration   G219
When we received the G219 in September 2022 it was in reasonable cosmetic condition. The exterior was dusty but largely undamaged, the rotors were present and, given its age, the lamp film was in reasonable condition. Apparently the machine has been stored in a humid place for many years, as there were signs of corrosion on the case shell and on the shiny metal parts.

After opening the top lid, it became clear that in the past the machine had been taken apart. The battery compartment was missing and the wiring harness to the lamp panel was rotated by 360°. There were no lamps present on the lamp panel, which is usually a good thing. Over the years we've seen many lamp films that had been damaged by installing the wrong type of lightbulbs.

We first removed the three rotors and cleaned their exterior and contacts thoroughly. We then traced the wiring of the rotors, to confirm that they had not been rewired by the Dutch Navy. All rotors have the original (commmercial) wiring.

Next, we cleaned the contacts of the entry disc (ETW) and the reflector (UKW). We also traced the wiring of the latter and confirmed that – like the rotors – it had not been rewired. In the next step the levers, pawls, pinions and cogwheels of the stepping mechanism were cleaned and oiled, after which the mechanism could be tested.
  
Contact pin (left) and contact plate (right) side

This was done by typing on the keyboard and observing the advancement of the three rotors and the UKW. Everthing worked as expected. Although the original crank was missing, we checked whether it was possible to rewind the mechanism by one or more steps, but this didn't work.

It appeared that the advance pawl was blocking the ratchet wheel on the ETW when the keyboard was in rest. The problem was caused by a worn-out rubber adjustment pad at the bottom of the chassis, below the pivoting point of the pawl.

The adjustment pad was dismounted from the chassis and the rubber remains were removed. A new rubber pad was then glued in its place and the adjustment pad was re-installed. It was then adjusted with a screwdriver (from the bottom) so that the pawl releases the ratchet wheel when the keyboard is in rest, as shown in the image.
  
Ratchet wheel actuator (pawl) in rest position

The ratchet wheel is now free when no key is pressed, and the crank can now be used to turn the mechanism in both directions. When pressing a key, the pawl first engages the ratchet wheel and then pushes it upwards. When the key is released, the pawl disengages the ratchet wheel again.

26 lightbulbs of the correct specifications were installed on the lamp panel and an external PSU was connected to the machine, so that a first test could be conducted. Only a few lamps lit up, indicating problems with the keyboard switches.

The keyboard was then dismounted from the chassis, so that the individual switches could be inspected. Some of the switches were misaligned and some of the rubber pushers at the end of a key shaft were missing or worn out. They were subsequently replaced by new rubber pushers that are fixated with a tiny drop of superglue.
  
Bottom view of keyboard unit

The rubber pushers operate the large seesaw at the bottom of the chassis, which in turn actuates the stepping mechanism at the rear. After mounting the keyboard back in place, the rubber pads at the front corners of the seesaw were adjusted for proper operation of all keys and switches.

The sloped lamp panel is hinged and is held in place by two screws located at the front edges of the lid. These screws mate with a treaded brass block that is fitted to a flange on the chassis. On the G219 these threaded blocks were missing, as a result of which the lid was not held in place. It is unknown why these blocks had been removed.

Suitable replacements were made from a solid piece of brass, and mounted in place as shown in the image on the right. The hole at the centre has 4 mm thread. The top lid is now properly retained when the machine is moved around.
  
Threaded brass block for lamp panel hold-down screw

In the next stage, the wiring for connection of a battery was restored. Two era-correct wires were added: one was connected to the lamp panel (visible in the image above) and the other one was connected to the common rail of the nearest switch below the keyboard. For the time being, the two wires will be fed out through the makeshift hole at the right side of the machine. They will later be connected to a replacement battery compartment as and when it becomes available.

Problems
  • Wooden case missing
  • Battery compartment missing
  • Crank missing
  • All lightbulbs missing
  • Mechanism misadjusted
  • Rubber pushers in keyboard worn out or missing
  • Crank won't turn mechanism back
  • Celluloid windows above wheel missing
  • Lamp panel hold-down nuts missing
  • Several screws missing from the outer case
Restored
Contact pin (left) and contact plate (right) side
Disintegrated adjustable rubber pad
Adjustable rubber pad below the ratchet actuator
Adjustment screw for the adjustable rubber pad under the ratchet actuator
Ratchet wheel actuator (pawl) in rest position
Ratchet wheel actuator engaged
Ratchet wheel actuator pushing up the ratchet wheel
Ratchet wheel and actuator (in rest position)
Keyboard section removed from the chassis
Bottom view of keyboard unit
Keyboard switches
Missing rubber keyboard pushers
Replaced rubber pushers
chassis bottom panel with keyboard-actuated stepping seesaw
Missing nut for lamp panel hold-down screw
Threaded brass block for lamp panel hold-down screw
Lamp panel hold-down screw
Restored battery wiring
Power wires
Power modification made by the Royal Dutch Navy
Serial number engraved at the bottom of the machine
Serial number engraved in the bottom panel, below the rotor stack.
Settable and movable reflector (UKW)
Seria number engraved in the hinge
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Contact pin (left) and contact plate (right) side
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Disintegrated adjustable rubber pad
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Adjustable rubber pad below the ratchet actuator
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Adjustment screw for the adjustable rubber pad under the ratchet actuator
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Ratchet wheel actuator (pawl) in rest position
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Ratchet wheel actuator engaged
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Ratchet wheel actuator pushing up the ratchet wheel
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Ratchet wheel and actuator (in rest position)
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Keyboard section removed from the chassis
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Bottom view of keyboard unit
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Keyboard switches
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Missing rubber keyboard pushers
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Replaced rubber pushers
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chassis bottom panel with keyboard-actuated stepping seesaw
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Missing nut for lamp panel hold-down screw
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Threaded brass block for lamp panel hold-down screw
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Lamp panel hold-down screw
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Restored battery wiring
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Power wires
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Power modification made by the Royal Dutch Navy
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Serial number engraved at the bottom of the machine
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Serial number engraved in the bottom panel, below the rotor stack.
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Settable and movable reflector (UKW)
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Seria number engraved in the hinge

Specifications
  • Device
    Cipher machine
  • Brand
    Enigma
  • Model
    G31
  • Designator
    Ch.15a
  • Serial number
    G219
  • Manufacturer
    H&R
  • Country
    Germany
  • Year
    1939 (est.)
  • Customer
    Dutch Navy
  • Rotors
    3
  • Turnovers
    17, 15, 11
  • Reflector
    Settable and movable (driven)
  • Wiring
    Standard commercial wiring
  • Stepping
    Irregular (cogwheel gear)
  • Plugboard
    No
  • Extras
    Crank, green sunlight filter (option)
  • Dimensions
    270 x 250 x 165 mm
  • Weight
    9.4 kg (7.2 kg without the wooden case)
Serial numbers
The serial number of this machine (G219) was found in the following locations:

Missing items
  • Wooden transit case
  • Battery compartment
  • Crank
  • Green filter
References
  1. David Kenyon and Frode Weierud, Enigma G: The Counter Enigma
    Bletchley Park and Crypto Cellar Research, 5 May 2019. Updated 15 June 2019.

  2. Personal accounts by former Dutch Navy personnel
    Crypto Museum, 2009.

  3. Livret Enigma G221 (maintenance booklet)
    Royal Dutch Navy. 10 Mar 1948 - 12 Marc 1955.
Further information
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Crypto Museum. Created: Sunday 18 September 2022. Last changed: Friday, 30 September 2022 - 22:25 CET.
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