In 2007, Simon Greenish, Director of Bletchley Park asked GCHQ Cheltenham for an additional Enigma machine – an ordinary 3 rotor unit that could safely be displayed as a “hands-on” machine for the public. Around October 2007, an Enigma duly arrived at BP. It was assumed to be a 3 rotor device so no one paid much attention to it. It was temporarily placed into the archive while plans were being drafted for a suitable box by the BP Education Officer. By December the machine received an examination. To everyone’s surprise what arrived at BP was a non-standard Enigma s/n T244 which was then identified as variant of the Enigma K machine namely the ‘Tirpitz’ - one specially designed for use in communications between Germany and Japan during WWII. It was called TIRPITZ by the Germans, and spelled as TIRUPITSU by the Japanese. Bletchley Park referred to it as the Tirpitz. The U.S. Navy named the machine as OPAL and the traffic that it generated as JN-18.
It goes without saying that such a rare machine cannot be subjected to hands-on use by the public so a special display case is being built for it. The search for a three rotor public-use Enigma continues.
The Enigma T is actually an Enigma K machine with some changes. Heimsoeth & Rinke, the machine's manufacturer provided rotors with special wiring and five notches on each rotor. In contrast to the Enigma K machines, which usually only came with one reflector and one set of three rotors, the Enigma T was equipped with one reflector and a set eight rotors. There was no stecker board . A detailed explanation follows the photos.
General view of machine. Lightboard and rotor window details. With cover open. A slightly different angle. With rotors removed and showing the serial number stamp. In this table, all photos are of Enigma Tirpitz s/n T244 and were taken by John Alexander G7GCK
|Closeup of Enigma Tirpitz rotors. (Photos by Mike Hillyard)|
THE TIRPITZ IN MORE DETAIL
John Alexander has kindly provided a transcription from the following document:
[Document marked] ‘TOP SECRET “ULTRA”
[National Archive Dept] /HW
G.C. & C.S. NAVAL CRYPTANALYTIC STUDIES
JAPANESE NAVAL ATTACHÉ MACHINE CYPHERS
- By –
JAPANESE NAVAL ATTACHÉ MACHINE CYPHERS 278
JNA 1 – THE TIRPITZ ENIGMA
- by –
JNA 1 – THE TIRPITZ ENIGMA 279
1 Narrative 280
2 Characteristics of the Text 281
3 Terminology 281
4 The Machine Described 281
5 The Key-lists 282
6 Settings and Indicators 282
7 The First Break-in: Initial deductions 282
JNA 1 – THE TIRPITZ ENIGMA 280
1. The Tirpitz or “T” Enigma was produced in Germany for Japanese use and during 1944 references were made in JNA 20 to the delivery of the machines. In August, a cargo including a consignment of Enigma Machines was sent to Lorient to await shipment to Japan by submarine, but it was still there when the Allied advance had enveloped the surrounding country and left Lorient as an isolated pocket. The Americans made a raid on the port and carried away a crate of sixty Enigma machines in the back of a Jeep. The Japanese knew nothing about this, and were in fact subsequently told by the Germans that the whole cargo had been destroyed. But other consignments had been delivered, and in September Berlin suggested distributing the machine to attachés in Sweden, Switzerland, Spain and Portugal. Tokyo agreed, and on 20th September sent out detailed instructions in JNA 10 as to how the machine was to be used. The first message in JNA 1, as it was called, was sent from Berne on 9th April 1945. Altogether, fifty-three messages were intercepted up to 15th May, when the traffic died. When the collapse of Germany seemed imminent and the central German administration was planning to evacuate Berlin, the Japanese Naval Attaché staff split into two groups. One group followed the Germans south to Badgastein, the other made for the Danish frontier and later crossed to Sweden. Both groups carried an Enigma machine, as the Coral had to be abandoned in the Berlin office.
Characteristics of the Text
2. The text of the messages was transmitted in five-letter groups preceded by two five-figure groups. The first of the figure
JNA 1 – THE TIRPITZ ENIGMA 281
Groups was the customary three-figure serial number and two-figure indication of whether the message was a complete telegram or one of a number of parts. The second group began with two-figures which were either both odd or both even. These remained unexplained, but it was noticed that the only two instances of even pairs appeared on messages not sent to Tokyo. The second two figures gave the date (01 to 31) and the last figure was a priority discriminant.
3. It must be emphasized here that JNA 1 was a special use of a common cypher, the Enigma, and it is only interesting as a deviation from the general trend and not as an independent study. The following details of the machine and the attack made on it are therefore written for the reader who is already acquainted with the general principles of the solution of the unsteckered Enigma, and the terminology current in the trade has been carefully preserved.
The Machine Described
4. The Tirpitz in an unsteckered machine with a movable Umkehrwalze and a hatted diagonal. There are eight wheels, three of which are used at a time. Each wheel has five turnovers distributed round the ring according to one of four patterns, so that there are two wheels to each turnover pattern. In operating the machine, the Japanese adopted the usual practice  of moving the Umkehrwalze forward one position by hand after the encypherment of every five-letter group.
 Such arbitrary hand advancement of machine wheels is called “Finnery”, the first observed cases being of the Finns’ treatment of their Hagelin machines. Other Hagelin users also used this trick but apparently BP first discovered this habit on the Finnish Hagelin links.
JNA 1 – THE TIRPITZ ENIGMA 282
5. The key-lists were concocted from JNA 10 encode book. In this book, the code groups are given as five-figure groups and also as five-letter groups derivable from the figures by means of a garble table. The wheel order and Ringstellung for the day were determined respectively by the figure and letter equivalents in the JNA 10 encode for the date of transmission (month and date of the month). The first three figures (passing over 0, 9 and repeated figures) determined which of the eight wheels were to be used and in which order, and the first four letters determined how the rings were to be set.
Settings and Indicators
6. When a message was to be enciphered, a window setting was chosen, apparently at random, for example X Q G B. This was encyphered on a pre-arranged Grundstellung in the form X Q G B B G Q X. Suppose the enciphered version was L D W C P J L Q, then the groups L D I W O and P J L T Q would be the indicators for the message (the underlined letters being dummies), and L D I W O would precede the transmitted text and P J L T Q would follow it. The Grundstellung were the first four letters of groups in the section of the encode devoted to ships. The recoveries in this section were so fragmentary that the system of selection could not be traced. All that is known is that a given group could serve as a Grundstellung for only one station and for only one day. Thus, if Berne and Tokyo both sent messages on the same day, they would use the same wheel order and rings, but different Grundstellungen
The First Break-in: Initial Deductions
7. The main attack on the traffic was launched when two messages were received which were suspected of being retransmissions of texts
JNA 1 – THE TIRPITZ ENIGMA 283
already deciphered on JNA 20. One of the messages was sent in JNA 1 in two parts of considerable length. The state of knowledge before the cribs from JNA 20 were applied to this. The traffic could not be definitely associated with Tirpitz, but there were two factors in favour of the assumption: the traffic was sent from posts known to have been allocated the machine, and a comprehensive frequency count of the texts did not exclude the possibility that the cypher had the non-crashing characteristics of the Enigma. It must be added that the second factor contributed very little, as strip cyphers such as JNA 22 were also non-crashing, and it was suspected that more versions of the strip cypher might appear. With special reference to the cribs, the clear messages in JNA 22 had the same spelling and punctuation symbols as in JNA 20, so that it seemed likely this would be true of JNA 1. By such deductions and analogies, three initial assumptions were made:
(a) The Tirpitz machine was being used as it had been captured;
(b) The clear text was spelt and punctuated as in JNA 20; and
(c) The text had not been deliberately paraphrased between the two encypherments.
Contributors and Credits:
1) John Alexander G7GCK Leicester, England. <jalex_uk(at)ntlworld.com>
2) Frode Weierud <Frode.Weierud(at)cern.ch>
3) Mike Hillyard , UK.
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