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Breaking German Navy Ciphers

U-534 was a German type IXC/40 submarine (U-boat) of the German Navy (Kriegsmarine) that was in service during World War II. The ship was built in 1942 by Deutsche Werft AG in Hamburg-Finkenwerder (Germany) and was designated 'werk 352'. It was launched on 23 September 1942 and commissioned on 23 December 1942. It was commanded by Oberleutnant Herbert Nollau [1].

Initially, the ship was assigned to the 4th U-boat Flotilla, but in April 1944, after some changes, it was transferred to the 2nd flotilla. On 1 May 1945 the boat went on its last patrol as part of the 33rd flotilla. Only five days later it was sunk by an attacking British Liberator aircraft. 49 of the 52 crew members survived the fatal blast.

Nearly 41 years later, in 1986, it was discovered by Danish wreckhunter Aage Jensen, on the sea bed of the Kattegat, off the coast of Denmark. Ten years later it was transported to the Warship Preservation Trust (WPT) in Wallasey (England).

There it was on public display for several years, whilst the Trust made plans to prepare the U-534 in such a way that visitors could go inside. But it was not to be. The dockland owners 1 wanted to sell the land off for luxury appartment development and the museum was forced to close down.

In 2006, the boat was acquired by a consortium involving the Merseyside Passenger Transport Executive (MPTE), and moved to the Woodside Ferry Terminal in nearby Birkenhead, where it was preserved and put on public display again. As there is limited space at the terminal, the U-534 had to be be cut into sections, which allows visitors to look inside without climbing aboard [6].

  1. All of the docklands in Wallasey, Birkenhead and Liverpool are owned by Peel Holdings.

Enigma messages
Many artefacts were recovered from the U-354 by Danish wreck diver Aage Jensen, such as weapons, equipment, bottles, name plates, stamps, breathing masks, clocks, binoculars, tools, etc. Amoung the recovered documents was also a large number of ciphertext Enigma messages.

As the contents of these messages was hitherto unknown German researcher Michael Hörenberg set out in 2012 to break the messages again by using distributed computing power.

Starting in July 2012 by combining 112 Intel CPU cores, using a modified software Turing Bombe and brute force attacks, he achieved his first break on 31 July 2012, based on a ciphertext-only attack. By 20 October, 46 of the 50 messages had already been broken again. One message, of 1 May 1945, is of particular historical importance, as it was sent by Dönitz.

Breaking the messages again is still very difficult, even with todays computing power. One of the main problems is the fact that most documents are damaged and are only partly complete and sometimes the start of the message is missing completely. Furthermore, the handwriting of the German operators is a challenge in itself. More information from Michael Hörenberg's website [3].

Message from Dönitz
This message was sent on 1 May 1945. It is of historical importance as it was sent by Admiral Dönitz to announce his apportment as Hitler's successor after the latter committed suicide.

The message was originated on an Enigma M4 machine and was broken again on 20 October by Michael Hörenberg and is reproduced here by his kind permission.

 Full message text


About the Warship Preservation Trust
The Warship Preservation Trust (WPT) was based in Birkenhead (Wirral, England) and hosted Europe's largest collection of preserved warships, until its demise in 2006.  Wikipedia
Apart from the U-534, there were several other vessels in the collection of the Trust:

  • HMS Plymouth (F126)
    One of the first Royal Navy Frigates to arrive at the Falkland Islands during the Falklands War of 1982. Following the demise of the Trust, the boat was towed to Türkiye in 2014 and scrapped.  Wikipedia

  • HMS Onyx (S21)
    Oberon-class submarine that was among the first boats to arrive at the Falkland Islands during the Falklands War of 1982, not only carrying its crew, but also a detachment of the Special Boat Squadrom (SBS). After the demise of the Trust, it was returned to Vickers in Barrow (UK) where it was built. In 2014 it was scrapped in Rosneath (UK).  Wikipedia

  • HMS Bronington (M1115)
    A Ton-class wooden-hulled minesweeper, launched on 19 March 1953, once captained by Prince Charles. The boat sank on the Birkenhead side of the docks in 2016 due to rotting.  Wikipedia
A number of letters and letter-combinations that are not frequently used in German, were used as puntuation marks in the text. The following markup codes were used by the German Navy:

X   Period
End of line or abbreviation (German: Punkt).
XX   Colon
(German: Doppelpunkt)
Y   Comma
YY   Dash, hyphen, slash
KK   Brackets, used as KK–KK
Text can be placed between parenthesis (brackets) by placing the letter combination 'KK' before and after it (Klammern). E.g. KKTULPEKK should be printed as (Tulpe).
J   Stress mark (or quote), used as J–J
It was possible to stress a certain part of the text by placing the letter 'J' before and after the text, e.g. REICHSLEITER J BOHRMAN J, could be printed as: Reichsleiter 'Bohrman'.
UD   Question mark (?)
  1. Wikipedia, German submarine U-534
    Retrieved October 2012.

  2. Diveship Ternen, Items found inside the U-534
    Website. Retrieved October 2012.

  3. Michael Hörgenberg, Breaking German Navy Ciphers
    The U-534 breaking project. July 2012.

  4. Oberkommando der Kriegsmarine, Der Schlüssel M, Verfahren M Allgemein
    Operating procedure for Naval Enigma. Berlin 1940.
    Crypto Museum #300359. 1

  5. Doppelbuchstabentauschtafeln für Kenngruppen
    Bigram substitution table for Message Indicators. Crypto Museum #300356. 1

  6. Dr. Bryan Roe, personal correspondence
    Wallasey, UK, June 2020.
  1. Document kindly supplied by Arthur Bauer.

Further information
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© Crypto Museum. Created: Friday 15 May 2015. Last changed: Saturday, 04 June 2022 - 07:53 CET.
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