In early 1939, the British government invited teams from Canada, Australia, New Zealand, and South Africa to visit the United Kingdom to be briefed on the then highly secret developments in radar.
As a ship passed over the loop, its magnetic properties would change the current flowing in the cable, which could be detected using conventional meters.
[2] In March 1940,[a] the Royal Canadian Navy asked the NRC if they could develop a system that would supplant the cable detector.
The receiver, a superheterodyne, sent its output to a 5 inches (130 mm) cathode ray tube with the timing set to a fixed maximum range of 10,000 yards (9,100 m).
[2] This unit was built by men from Research Enterprises Limited (REL) in Toronto who had been sent to the NRC in Ottawa to learn radio technique.