 Simultaneous with "Wilde Sau", "Zahme Sau" (Tame Boar) was introduced, in which the twin-engined night fighters in to the "Himmelbett" system using individual ground-controlled interception were released.The fighters flew against the bomber stream in a co-ordinated operation over a wide area, guided by a running commentary derived from radar, ground observation, wireless interception and contact reports from aircraft tracking the bomber stream.Audio and visual beacons were used to assemble the fighters, which circled the beacons until the target was known and then intercepted the bombers, above a height beyond which the "flak" did not fire.