The "Luftwaffe" in 1940 primarily relied on three twin-engined medium bombers: the Dornier Do 17, the Heinkel He 111 and the Junkers Ju 88. Despite the "Luftwaffe" being in the possession of advanced gyroscopic bomb sights, the "Lotfernrohr 7" for daylight bombing and electronic navigational aids like the Knickebein, X-Gerät and Y-Gerät for nocturnal bombing, there were some very fundamental limitations to the accuracy of bombing from level flight, and there was no guarantee that such attacks could achieve success on small or difficult targets such as radar stations.