Government Code and Cypher School: ISOS Section and ISK Section: Decrypts of German...

This series consists mainly of decrypts of German Secret Service messages decrypted by the Government Code and Cypher School. The series started with the nomenclature ISOS - intelligence service Oliver Strachey - and ISK - intelligence service Knox, relating to senior staff members.

Strachey was head of the section responsible for breaking Abwehr hand cyphers and for issuing all reports on the German Secret Services. Knox headed the section responsible for breaking Abwehr machine cyphers in December 1941. Messages are of enormous variety and relate to almost all aspects of the war.

There were also a number of smaller series, including ISOSICLE (Sicherheitsdienst messages). The major recipient of these reports was Section V of MI6, and this series includes some reports, studies and correspondence originating from sub-sections of Section V. Also included in the series are internal studies and working aids produced by ISOS section, intelligence reports on the German Secret Services and some captured material.

Finally, a series of logbooks containing original German language decrypts in true order for Berlin-Rome correspondence are preserved to demonstrate the records formed in the typical process of decryption. This series of logbooks has been selected as a typical example, and other logbooks for correspondence on other links has not been selected for permanent preservation in The National Archives. These logbooks have instead been presented to the Bletchley Park Trust under s 3(6) of the Public Records Act 1958.

Former reference order.

See also HW 34

From 1999 Government Communications Headquarters

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Intelligence

The Abwehr was the intelligence service of the German high command. Its personnel used radio networks throughout Europe, South America and the Middle East, including occupied and neutral territories. The Sicherheitsdienst was responsible for political intelligence, organisation of fifth columns and dissemination of Nazi propaganda, and had its own radio network. The Radio Security Service (from 1939 to 1940 under the War Office MI 8, and then under MI 6) passed intercepted messages to GCCS. ISOS section worked closely with the analytic section of the Radio Security Services, which produced a number of studies and reports also to be found in this series (HW 19/331-333).