From a Telegraph obituary about a death on July 8, 2013:
"The pilots’ tactic was to fly to within a certain distance of the target, and cut their engines. They would then glide in silently, release their bombs, then restart their engines and fly home. The Germans called them the 'Nachthexen' (the Night Witches) due to the whooshing sound they made— 'like a witch’s broomstick in the night'— as they flew past. There was, supposedly, a promise to award an Iron Cross to any Luftwaffe pilot who actually managed to bring down a Night Witch."
In memoriam: