'Y' Service was the study of external features of under coded wireless traffic, traffic analysis and the breaking of low-grade ciphers.

Wireless intelligence sections were developed soon after Dunkirk May - June 1940. There were approximately 40 special wireless sections (SWS) in the years 1939 to 1945. About thirty mobile sections were active with fighting troops on all fronts. However interception of former and potential enemy forces was well established between the wars.

Voluntary Intercept Service consisting of operators, often amateur radio operators and short wave listeners.

There were three types of  (SWS)
A Type were Army HQ units
B  Type were Corps HQ units
C  Type was formed at Radlett, England for jamming of enemy wireless and radar transmissions this unit was made up from an ATS unit.