The Rebecca/Eureka transponding radar was a short-range radio navigation system used for the dropping of airborne forces and their supplies. It consisted of two parts, the Rebecca airborne transceiver and antenna system, and the Eureka ground-based transponder. Rebecca calculated the range to the Eureka based on the timing of the return signals, and its relative position using a highly directional antenna. The 'Rebecca' name comes from the phrase "Recognition of beacons". The 'Eureka' name comes from the Greek word meaning "I have found it!".