The American historian David Kahn underscored the war-historical significance of this cryptography and cryptanalysis success of Tranow, citing an anonymous source: Wilhelm Tranow initially worked as a radio technician aboard the battleship Pommern.

In 1914, he received a coded message, while on watch, from the cruiser Breslau which he forwarded to fleet command, who reported they could not read it.

Showing a lack of urgency and understanding, Fleet HQ issued Tranow a stern warning to keep away from secret matters, instead of trying to improve the code.

[6] In late 1919, Tranow reconstructed Britain's enormous Government Telegraph Code which was used by the Admiralty to carry reports about warships.

[7] From early 1932 he started work on Code Signaux Tactiques that provide insight into French tactics.

These early successes led gradually to the growing strength of his unit, which was now called B-Dienst (German: Beobachtungsdienst).

[2][8][9] Tranow's growing influence and the increasing importance of his specialty ensured his rise within B-Dienst and eventually, sometime after 1936 he was charged with running the complete cryptanalyst section, even though he was not a Nazi.

On 11 September 1939 this bore immediate fruit when the B-Dienst read a British message which indicated the assembly points of z convoy.

Exact data on British counter-measures such as landing fields, and the arrival of transports at Harstad were known in advance, enabling German Armed Forces to take appropriate action.

4 codebook from a merchant vessel in northern waters[14] enabled Tranow to make limited penetrations of British Naval Cipher No.