A precision VHF radio beam navigation and bombing system.

"Crooked Leg" - German navigational system using radio beams to guide bombers

Knickebein ("crooked leg" in German, but also the name of a magic raven in a German fairy tale) was a radio navigation system used by the Luftwaffe early in World War II to aid bomber navigation. It was replaced with the X-Gerät (navigation) system.