Short Weather Cipher
The Short Weather Cipher (German:Wetterkurzschlüssel), also known as the weather short signal book was a cipher, presented as a codebook, that was used by the radio telegraphists aboard U-boats of the German Navy (Kriegsmarine) during World War II. It was used to condense weather reports into a short 7 letter message, which was enciphered by using the naval Enigma and transmitted by radio men to intercept stations on shore, where it was de-enciphered by Enigma and the 7 letter weather report was reconstructed.[1][2]
History
During World War II, during various times, different versions of the cipher were in operation. The first issue carried the code name Weimar. It was replaced by the edition Eisenach on 20 January 1942. On the 10th of March, 1943, the third edition of the weather key, bearing the codename Naumburg, entered into force.
On May 9, 1941, during Operation Primrose, the operation to occupy Åndalsnes and create a diversion south of Trondheim in Norway as part of the Norwegian Campaign,[3] an intact Naval Enigma (M3) cipher machine, a copy of the "Weimar" version of the short weather cipher and a copy of the short signal book was recovered from the submarine U-110, that was captured in the North Atlantic east of Cape Farewell, Greenland.[4] This enabled the cryptanalysts in Bletchley Park to break the encryption of the M3 and to decipher the German submarine radio messages.
On October 30th, a copy of the Wetterkurzschlüssel, the short weather cipher, and the short signal book, the Kurzsignale, were recovered as part of a daring raid on the U-boat U-559, when three Royal Navy sailors, Lieutenant Anthony Fasson, Able Seaman Colin Grazier and NAAFI canteen assistant Tommy Brown, then boarded the abandoned submarine, and recovered the documents after an 90 minute search.[5] They reached the Government Code and Cypher at Bletchley Park after a three week delay, on November 24th 1942. The documents which cost the lives of Fasson and Grazier, proved to be particularly important in breaking the Naval Enigma M4.
Operation
The short weather cipher coded weather reports using a polyphonic single letter code with X missing.[6]
A= +28° ◦ B = +27° ◦ C= +26° ◦ D= +25° ◦ . . . W= +6° ◦ Y= +5° ◦ Z = +4° ◦
A= +3° ◦ B = +2° ◦ C= +1° ◦ D= 0° ◦ E =−1° ◦ F =−2◦ . . . Z = −21° ◦
In a similar way, water temperature, atmospheric pressure, humidity, wind direction, wind velocity, visibility, degree of cloudiness, geographic latitude, and geographic longitude had to be coded in a prescribed order with the weather report consisted of a single short word. Based on the approximate knowledge of the position of the submarine, the Kreigsmarine telegraphist who received the message could translate the letter "S", according to the above table, which could mean 10 °C or -15 °C, back to the correct temperature.
Similarly, the direction and the nature of which was swell with also only a single letter codes:
-------------------------------------------------- as shown in Fig. Direction from which Type of swelling The swell comes low middle high | high | -------------------------------------------------- as shown in Fig. N | a | i | q | NO | b | j | r | O | c | k | s | SO | d | l | t | S | e | m | u | SW | f | n | v | W | g | o | w | NW | h | p | x | No swelling | | | y Intermittent | | | | e.g.,
An example of the cipher would be be 68° North latitude, 20° West latitude (northwest of Iceland), atmospheric pressure 972 millibars, temperature minus 5° Celsius, wind northwest Force 6 (on the Beaufort scale), 3/10 cirrus cloud cover, visibility 5 nautical miles, would become MZNFPED.[7]
Publications
- Arthur O. Bauer: Direction finding as Allied weapon against German submarines from 1939 to 1945. Selbstverlag, Diemen Netherlands 1997. ISBN 3-00-002142-6
- Friedrich L. Bauer : Decrypted Secrets. Methods and Maxims of Cryptology. 4rd revised and expanded edition. Springer, Berlin and others 2007 ISBN 3-540-24502-2.
- Paul N. Pfeiffer:. Breaking the German Weather Ciphers in the Mediterranean Detachment G - 849th Signal Intelligence Service Cryptologia , Vol 22 (4), October 1998, page 354-369.
- Heinz Ulbricht: The Enigma cipher machine - Deceptive security. A contribution to the history of the news services. Dissertation Braunschweig 2005. PDF; 4.7 MB
References
- ^ T. W. Körner (5 December 1996). Trinity Hall (ed.). The Pleasures of Counting. Cambridge University Press. pp. 399–. ISBN 978-0-521-56823-4.
- ^ "Codebreaking and the Battle of the Atlantic David Kahn" (PDF). USAFA Harmon Memorial Lecture #36. p. 8. Retrieved 27 April 2016.
- ^ David Brown (5 November 2013). Naval Operations of the Campaign in Norway, April-June 1940. Taylor & Francis. p. 78. ISBN 978-1-135-27377-4.
- ^ Hugh Sebag-Montefiore (21 July 2011). Enigma: The Battle For The Code. Orion. p. 88. ISBN 978-1-78022-123-6.
- ^ David Kahn (2012-01-01). Seizing the Enigma - The Race to Break the German U-Boat codes 1939-1943. Annapolis: Naval Institute Press. pp. 255–264. ISBN 978-1-59114-807-4.
- ^ Bauer, Frederich l. (2007). Decrypted Secrets. Methods and Maxims of cryptography (4th ed.). Springer. p. 73. Retrieved October 21, 2016.
- ^ T. W. Körner (5 December 1996). The Pleasures of Counting. Cambridge University Press. pp. 399–. ISBN 978-0-521-56823-4.