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Enigma T   Tirpitz
The Japanese Enigma - wanted item

Enigma T, codenamed Tirpitz, was an Enigma cipher machine made during WWII by Heimsoeth und Rinke (H&R) in Berlin (Germany) especially for use by the Japanese Army. It was based on the commercial Enigma K, but came with eight cipher rotors, three of which were in the machine. In addition, each rotor had five turnover notches, which caused in an irregular stepping behaviour. All rotors plus the entry disc (ETW) and the reflector (UKW) were wired uniquely for the Japanese.

The machine was intented for communication between the Japanese Navy and the German Navy (Kriegsmarine). The agreement for this was signed on 11 September 1942 by German Vice Admiral Erhard Maertens and Japanese Admiral Tadao Yokoi. At the time, Maertens was Director of the German Naval Communication Service and Yokoi was the Japanese Naval Attaché in Berlin. This followed the earlier Japanese-German Military Agreement of 18 January 1942 [2].

All German-Japanese communication would be encrypted with a machine that was referred to as Enigma T. The Germans called the operating procedure TIRPITZ, whilst the Japanese named it TIRUPITSU. The US Navy referred to the machine as OPAL whilst its traffic was named JN-18 [2]. The official name for the machine system was Japanese-German Joint Use Code No. 3.

The machine was used with an operational procedure – TIRPITZ – and a key list – GARTENZAUN (garden fence). The procedure (Tirpitz) came into effect on 1 August 1943 and was used for the remainder of the war. The key list (Gartenzaun) was divided into two periodes: 1 August 1943 to 31 December 1943 (Gartenzaun 1) and 1 January 1944 to the end of the war (Gartenzaun 2). Most of the information on this page is based on Frode Weierud's article TIRPITZ and the Japanese-German Naval War Communication Agreement in Cryptologia of July 1999 [2].

It is not exactly known how many Enigma T machines were actually built. The Japanese ordered 800 machines, but for various reasons this quantity was never delivered. There were delays in design and manufacture, and it became increasingly difficult to get sufficient supply of materials. Furthermore, the Germans had their doubts about the security of the machine. In the meantime, the Japanese used two manual systems: Sumatra (later: Sumatra 2) and TOGO (later: TOGO 2).

The Enigma T is based on the design of Commercial Enigma K (A27) and not the more common Steckered Enigma I that was used by the German Armed Forces. As the machine was intended for encrypting the wireless communication between the German and Japanese Navies, a strong cipher was mandatory. At the same time, the German didn't want to share their most secret machine (Enigma I). As a compromise, they took a commercial Enigma K and improved it in several ways.

The entry disc (ETW) was wired differently from all other machines — not in the order of the alphabet or the keyboard. In addition it came with 8 rotors, 3 of which were placed in the machine. In addition, each rotor had 5 turnover notches, as shown in the image on the right.

It caused a more frequent turnover of the rotors and increased the cipher period (as 5 is a relative prime of 26). 1 Additional complexity was some­times added, by instructing the user to advance the settable reflector (UKW) by one position by hand after each fifth 5-letter group (25 letters).

The first order for Enigma T machines was for 400 units, but this order was never fully delivered. Due to material shortages, only small batches of machines were supplied to the Japanese. Some shipments got losts whenever the carrying U-boat was sunk and one machine was compromised in Guadalcanal on 15 February 1943. German codebreakers experimented with the machine and started doubting its security, especially when it was used for large volumes of traffic.

In June 2009 we were allowed to photograph an Enigma T rotor III. This rotor belongs to the Tirpitz Enigma with serial number T47, which is part of the internal collection of the British Intelligence Service GCQH. Shortly afterwards, GCHQ unexpectedly donated the Enigma T with serial number T244 to the Bletchley Park Museum, which has since been on public display.

  1. It also introduced a weakness as the number of notches on each rotor now share a common factor (five).

Left side of rotor 3
Right side of rotor 3
Side of rotor 3
Left side of rotor 3
Right side of rotor 3
1 / 5
Left side of rotor 3
2 / 5
Right side of rotor 3
3 / 5
Side of rotor 3
4 / 5
Left side of rotor 3
5 / 5
Right side of rotor 3

Proposal for a new Enigma
Apparently, the Japanese had acquired the manufacturing rights for the Enigma T, as on 18 May 1943 they cancelled their order. Around the same time, the Germans proposed a new type of machine for joint communication use: the 02562-A-Enigma. According to a report, this is a Steckered machine, most likely based on the standard Service Enigma. The Germans proposed to replace the remainder of the order (another 400 machines) with this new type.

Part of the initial batch of 400 machines had already been delivered however, and some were still in production. After the Japanese Naval Attaché expressed his concern about this, the Germans guaranteed that the new machine would be interoperable with the old one. Using the new machine without plugs (Steckern) would make the machine compatible with the Enigma T.

If this was the case, the machine would cryptographically be considerably stronger than the Service Enigma. It would combine the strength of the plug board with more frequent turnovers and an increased cipher period. Had it been possible to deploy this machine widely, it might have defeated the American and British codebreaking efforts. However, at this point during the war, the material shortages made it impossible to build large quantities of any machines.

Captured machines
From then on, small batches of the new machine were delivered to Japan, whilst the initial order for Enigma T machines was also (partly) fulfilled. In August 1944, a large batch of Enigma T machines was captured by the Allied Forces in a warehouse in the vicinity of Lorient. Although there are conflicting accounts, it is likely that some 70 machines were captured there.

T-244 for Bletchley Park
When Bletchley Park was first opened as a museum, around 2000, they had an Enigma on display that could be touched by the public. It was part of the so-called Crypto Trail that allowed visitors to follow the flow of an Enigma message. At the end of the trail was a real Enigma. Researchers discovered however, that the machine on public display was an extremely rare Enigma M3 — the standard machine used by the Kriegsmarine (German Navy), of which very few have survived.

The machine was removed from the hands-on exhibition in 2007 and was locked away in BP's safe. Since 2011 it is back on public display again — as part of the main Enigma display — but this time protected by bullet-proof glass.

As they wanted another machine for the hands-on experience, BP director Simons Greenish asked GCHQ in mid-2007 for a spare Enigma machine of which they had more than one available. He assumed to be given a standard German Army 3-rotor Steckered Enigma, but instead in October 2007 he received a surprise.

The machine that GCHQ had given BP was a non-Steckered machine with 4 adjustable rotors. After a closer examinition it turned out to be the extremely rare Enigma T, with serial number T-244. The machine was in pretty bad condition and its wooden case was missing completely.

Furthermore, there was no serial number plate on the machine's body and the paint had deteriorated somewhat. Nevertheless it is probably one of the best unexpected gifts that Bletchley ever received. The machine has since been restored and is now part of the permanent Engima display in B-Block. Another Enigma T machine is on public display at the NCM.

The table below shows the wiring of the Enigma T rotors, the entry disc (Eintrittswalze, ETW) and the reflector (Umkehrwalze, UKW) [1]. The rightmost column shows what letter is visible in the window when the rotor causes a turnover of the rotor to its left. Please note that these positions are different from the actual position of the notches on the circumference of the rotor.


  1. Note that this is the only machine with a different wiring for the ETW. All other Enigma machines have an ETW that is wired either in the order of the alphabet (ABCDEF...) or the order of the keyboard (QWERZU...).

JN-18 traffic (i.e. messages encrypted on Enigma T) was rarely intercepted by the Americans and was therefore very difficult to break. At the end of the war, Enigma T was used by the Japanese Naval Attachés and even for diplomatic traffic after the Japanese had destroyed their PURPLE machines. It is known to have been used between stations in Tokyo, Berlin, Stockholm and Bern. The exact operating procedure is still unknown. In 2009, Frode Weierud published four original Enigma T messages on his website, all of which have since been broken [3].

The image above shows a real Japanese Enigma-T message as it was intercepted on 10 March 1944 by the US Navy's signal intelligence and cryptanalytical group OP-20-G. More sample messages and historical backgrounds are available from Frode Weierud's website [3].

  • Device
    Cipher machine
  • Brand
  • Type
  • Model
    A27 (modified)
  • Designator
  • Codename
  • Manufacturer
  • Quantity
    300-400 (est.)
  • Country
  • Year
  • Customer
  • Rotors
    3 (from a set of 8)
  • Turnovers
    5 per rotor
  • Reflector
  • Wiring
  • Stepping
    Irregular (Enigma stepping)
  • Plugboard
  • Extras
  • Enigma T
    Manufacturer type number
  • T-Enigma
    Variation to the above
  • Tirpitz
    Codename used by the Germans
  • Tirupitsu
    Codename used by the Japanese
  • OPAL
    Codename used by the Americans
  • JN-18
    Allied identifier for Enigma T traffic
  • No. 3
    Japanese-German Joint Use Code
Surviving machines
  1. David Hamer, Geoff Sullivan and Frode Weierud,
    Enigma Variations: An Extended Family of Machines

    Cryptologia, July 1998, Volume XXII, Number 3, pp. 211-229.

  2. Frode Weierud, TIRPITZ OPAL
    TIRPITZ and the Japanese-German Naval War Communication Agreement.
    Cryptolog, July 1999, Volume XX, Number 3, pp. 6-10.

  3. Frode Weierud, German Enigma T (Tirpitz) Messages,
    used for Japanese-German Intercommunications.

  4. Daniel J. Girard, Breaking "Tirpitz":
    Cryptanalysis of the Japanese-German joint naval cipher

    Cryptologia 40:5, January 2016, pp. 425-451
Further information
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Crypto Museum. Created: Tuesday 11 August 2009. Last changed: Monday, 30 October 2023 - 08:35 CET.
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