The Y Service 1939-1945

Bletchley Park sections

This document may be useful when read in conjunction with the Bletchley Park Roll of Honour.


The organisation at Bletchley Park was made up of a number of sections. The table below gives brief details of some of these.

Name Details
Air Section Non-Enigma enemy codes and ciphers. There was also a sub-section of Hut 3, referred to as the Hut 3 Air Section or Air Intelligence Section, producing intelligence from Luftwaffe Enigma signals.
Cover, Traffic and Records (CTR), later CoverManagement Y (CMY) Controlled Y service interception of diplomatic and commercial wireless networks
Central Signal Registry(CSR) Subsection of Communications Section, handled all incoming and outgoing signal traffic.

Distribution and Reference
Mechanism for distributing intelligence reporting.
Intelligence Exchange (IE) Formed in 1941 to replace Distribution and Reference for intelligence reporting on naval, army andair force matters.
Hut 3 German Army and Air Force Enigma Reporting Section. Produced intelligence reports from signals
deciphered by Hut 6. This section continued to be referred to as “Hut 3” after moving to Block D inFebruary 1943.
Hut 4 See Naval Section.
Hut 6 Location of German Army and Air Force Enigma Processing and Decryption Section. This section
continued to be referred to as “Hut 6” after moving to Block D in February 1943.
Hut 8 Location of German Navy Enigma Processing and Decryption Section from February 1940. This
section continued to be referred to as “Hut 8” after moving to Block D in February 1943.
Illicit Signals Knox (ISK) Deciphering of Abwehr (German Intelligence Service) Enigma coded signals. Initially headed by Dilly
Illicit Signals Oliver Strachey (ISOS) Deciphering of Abwehr (German Intelligence Service) manually coded signals. Initially headed byOliver Strachey.
Inter-Service Special Intelligence School ISSIS) Training school in Bedford for cryptographers, from 1941. Also provided Japanese language courses
from 1942.
JAFO Japanese Forces. Team formed in 1944 to work on Japanese army and air targets.
Military Section Later Military Wing.
Naval Section Sometimes referred to as “Hut 4”. Responsible for intelligence from naval Enigma messages deciphered in Hut 8 and also for deciphering and exploiting non-Enigma naval ciphers. Located in Hut 4 from 1940 to mid 1942, then in Blocks A and B.
No 4 Intelligence School(4 IS or IV IS) Cover name given by the War Office to the Military Section or Wing of BP.
SIXTA Responsible for Traffic analysis - the study of communications links, call-signs, frequencies and timings and lengths of transmissions, to build up a picture of the enemy's organisation, routine and dispositions. Name formed from No 6 Intelligence School and Traffic Analysis.
Wireless Telegraphy Coordination (WTC) Controlled Y Service cover of enemy, naval and air force wireless networks


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