Y service
The "Y" service was a network of British signals intelligence collection sites, the Y-stations. The service was established during the First World War and used again during the Second World War. The sites were operated by a range of agencies including the Army, Navy and RAF plus the Foreign Office (MI6 and MI5), General Post Office and Marconi Company receiving stations ashore and afloat. There were more than 600 receiving sets in use at Y-stations during the Second World War. Background. The "Y" stations tended to be of two types, for intercepting of the signals and  for identifying where they were coming from. Sometimes both functions were operated at the same site, with the direction finding (D/F) hut being a few hundred metres from the main interception building, because of the need to minimise interference. The sites collected radio traffic which was then either analysed locally or if encrypted, passed for processing initially to the Admiralty Room 40 in London and during World War II to the Government Code and Cypher School at Bletchley Park in Buckinghamshire. In the Second World War a large house called "Arkley View" on the outskirts of Barnet (now part  of the London Borough of Barnet) acted as a data collection centre, where traffic was collated and passed to Bletchley Park and it also acted as a Y station. Many amateur radio (ham) operators supported the work of the Y stations, being enrolled as "Voluntary Interceptors". Much of the traffic intercepted by the Y stations was recorded by hand and sent to Bletchley by motorcycle couriers and later by teleprinter, over post office land lines. The name derived from Wireless Interception (WI). The term was also used for similar stations attached to the India outpost of the Intelligence Corps, the  Wireless Experimental Centre (WEC) outside Delhi. Direction-finding Y stations. Specially constructed Y stations undertook direction finding on wireless transmissions. This became particularly important in the Battle of the Atlantic where locating U-boats was vital. Admiral Dönitz told his commanders that they could not be located if they limited their wireless transmissions to under 30 seconds, but skilled D/F operators were able to locate the origin of their signals in as few as six seconds. The design of land-based D/F stations preferred by the Allies in World War II was the U-Adcock system, which consisted  of a small, central operators' hut that was surrounded by four vertical aerial poles, usually placed at the four compass points. Aerial feeders ran underground, and surfaced in the centre of the hut where they connected to a direction finding goniometer and a wireless receiver, that allowed the bearing of the signal source to be measured. In the UK some operators were located in an underground metal tank. These stations were usually in remote places, often in the middle of farmers' fields. Traces of Second World War D/F stations can be seen as circles in the fields surrounding the  village of Goonhavern in Cornwall.