Catalogue description Government Code and Cypher School: Naval Section: Reports, Working Aids and Correspondence

The origins of the Naval Section of the Government Code and Cypher School lie in the 1920s, when the Admiralty took an interest in the development of the Japanese navy. The work of the Section remained low-key until 1934, when intensive effort on European targets began with the breaking of the Italian Naval code at a time when the belligerence of Italian foreign policy was a cause for concern. No interest was taken in German naval traffic until 1936, when numerous German naval transmissions using the ENIGMA machine cypher were intercepted. These messages remained unbroken at the time. Unable to break into the code, the Section had recourse instead to external analysis of wireless communications to derive intelligence from them (known as 'W/T I'). In August 1939 the German W/T I sub-section was transferred from GC&CS to the Naval Intelligence Division of the Admiralty.

As a result of this action, when Frank Birch, veteran of naval code breaking in Room 40 during the First World War was recalled to Bletchley Park in September 1939, he found that the German naval sub-section consisted himself and two other members of staff. The section soon expanded dramatically, taking over again the W/T I work previously transferred to the Admiralty, breaking the German naval ENIGMA code, and employing huge numbers of cryptographers, analysts and reporters to process the intercepted communications and supply intelligence to the British and Allied Commands.

Birch, who along with Nobby Clarke (head of the Naval Section from 1939 until mid-1941) had written the war history of the operations of Room 40 after the First World War (see HW 7) assiduously collected written material relating to the work of the Naval Section to provide a war record, and this is included among the Naval Section headquarters correspondence in this series.