Units that engage in the interception and exploitation of the patterns and substance of an enemy’s low-grade signals traffic. Intelligence gained through the Y-service is typically used in the reconstruction of the enemy’s order of battle and movements; however, it also provides important strategic intelligence. For example, on 20 May 1942 the Royal Air Force Y-service in North Africa learned that the total amount of enemy aviation fuel in the whole of Libya was only a paltry 3,283 tons.
This information enabled the RAF to gauge the effect of its interdiction campaigns and helped to predict enemy combat capability. More important to operations was the interception of enemy radio messages that contained intelligence on the locations of enemy units, early warnings of enemy air raids, as well as enemy tactics. This intelligence was intercepted, interpreted, passed along to the group controller and to Headquarters Northwest African Tactical Air Force, and aided in focusing Allied airpower against the most profitable targets.
References Clayton, Aileen. The Enemy is Listening. London: Hutchinson, 1980. Gladman, Brad.“Air Power and Intelligence in the Western Desert Campaign, 1940–1943.” Intelligence and National Security 13, 4 (Winter 1998). Public Record Office. AIR 40/2345 ‘Y’ Daily Reports Middle East for 20 May 1942. Public Record Office. AIR 23/1710. Memorandum entitled Wireless Intelligence circulated by the Chief Intelligence Officer,NWATAF, 13 May 1943. Public Record Office, Kew, Surrey.