In one of their few intelligence successes during the War, the Germans managed to get back to RAF aircrew that IFF would jam the blue master radar guided searchlights - pilots would switch on the IFF and some of the blue searchlights would wander around as if not under direction. Despite strict orders to the contrary, crews would leave IFF switched on as they approached searchlight belts, little knowing that the bomber stream was being tracked by their own IFF transmissions. The bomber stream appeared as flames on the German radar screens, and this became the German codeword for detection by this method: "Flamen". Once the route of Main Force was calculated then night fighters using NAXOS which picked up the H2S radar at about 60km were directed towards the bombers, . At 10km from the bomber stream, Flensberg would pick up individual bombers Monica transmission allowing them to be tracked into 5km range where the night fighter's own radar took over until visual, and a descent under the bomber to allow attack by Schragemusik. Very efficient: very lethal.