Rebecca/Eureka transponding radar
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 system was developed in the UK at the Telecommunications Research Establishment by Robert Hanbury Brown and John William Sutton Pringle.
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.
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 a test flight in February, the aircraft was flying at 20,000 feet (6.1 km) when Hanbury Brown's oxygen supply failed and he passed out.
[2] This accident, along with the many previous flights at high altitude, aggravated an ear injury he had received at RAF Martlesham Heath in 1939, and during the spring he was hospitalized for a mastoidectomy operation in Brighton.
Brown had missed most of the development of this system, and he was no longer allowed to fly at high altitudes, so his work on AI ended.
He was instead placed in a new group led by John Pringle, a zoologist from Cambridge University, and the two began to study new applications for radar technologies.
The Army Co-operation squadrons carried out a variety of missions including artillery spotting, general reconnaissance, and ground attack.
He found the group was only mildly interested in radar, thinking it might make a useful device for warning of the approach of enemy fighters, but were perfectly happy using flags and smoke signals for navigation and communications.
[3] Brown then visited a military exercise involving ground attacks in close coordination with the Army, and was convinced that radar systems could be used to improve these results.
In a long conversation, the two outlined the possibilities of radar for bombing, navigation and return-to-base roles, all of which proved to be interesting to Barratt.
Both Pringle and Brown then focused on the use of a transponder system combined with existing radars to allow accurate bombing or delivery of supplies or troops by parachute, a role that would almost always be carried out by twin-engine aircraft or larger.
[4] To illustrate the concept, Brown gave them a small transponder and told them to hide it anywhere within 15 miles (24 km) of Army Co-operation headquarters in Bracknell.
Just as Brown managed to convince them they were not spies, their own aircraft, a Bristol Blenheim, arrived and fired a smoke signal only 50 yards from the transponder.
[5] A more immediate outcome of the visit to Ringway was an invitation for Brown to meet a secret group known as the Special Operations Executive (SOE) at Whitehall.
On 11 February 1942 one of the TRE's Avro Ansons took off from RAF Hurn and picked it up at a range of 37 miles (60 km), approaching and dropping two containers within 200 yards.
[7] As the SOE had their own aircraft, and there was no need to make the system work with an existing production radar design, the solution was relatively simple.
The solution was found to be small nickel-iron batteries that could be repeatedly and rapidly recharged in the field, and operated across a wide range of temperatures.
To protect the system from capture, it was fitted with small explosives that would destroy enough of the circuitry to make it impossible to determine the exact frequencies being used.
When many British military gliders failed to reach their landing zones in Sicily even in excellent conditions, a rushed effort to develop an even smaller and lighter Rebecca III system started.
As the Rebecca units approached the Eureka the return signal would eventually overlap the interrogation pulse, and render the system ineffective.
