Eureka beacon

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!".

The system was developed in the UK at the Telecommunications Research Establishment by R. Hanbury-Brown and J.W.S. Pringle. Rebecca was essentially an ASV naval radar fit to a new broadcaster unit, while the Eureka system was all-new. Initial production began in 1943, and the system was used for dropping supplies to resistance fighters in occupied Europe, after delivery of the portable Eureka unit. The US Army Air Force started production in the US as well, and both examples could be used interchangeably. Over time, the Rebecca/Eureka found a number of other uses, including blind-bombing, airfield approach, and as a blind-landing aid in the BABS (Beam Approach Beacon Signal) form.

As many of the war-era systems used similar display units, the Lucero system was introduced to send the proper signals to interrogate any of these systems, allowing a single display unit of any type to be used for H2S, ASV, AI, Rebecca and BABS.

Rebecca/Eureka owes its existence largely to the efforts of Robert Hanbury Brown, an astronomer and physicist who worked with the Air Ministry's AMES group on the development of radar. During 1940, Brown had led development of a new version of the AI Mk. IV radar that included a pilot's indicator, better known today as a C-scope. This display directly represented the relative position between the fighter and its target, as if the pilot were looking through a gunsight. It was hoped that this would greatly ease the problems that the radar operators had trying to relay instructions from their instruments to the pilot, especially at closer range.

...
Wikipedia