GEE (navigation)

Gee, sometimes written GEE, was a radio navigation system used by the Royal Air Force during World War II. It measured the time delay between two radio signals to produce a fix, with accuracy on the order of a few hundred metres at ranges up to about 350 miles (560 km). It was the first hyperbolic navigation system to be used operationally, entering service with RAF Bomber Command in 1942.

Gee was devised by Robert Dippy as a short-range blind landing system to improve safety during night operations, but during development by the Telecommunications Research Establishment (TRE) at Swanage it was found the range was far better than expected and it developed into a long-range general navigation system. For large, fixed targets, like the cities that were attacked at night, Gee offered enough accuracy to be used as an aiming reference without the need to use a bombsight or other external reference. Jamming reduced its usefulness as a bombing aid, but it remained in use as a navigational aid in the UK area throughout the war.

Gee remained an important part of the Royal Air Force's suite of navigation systems in the post-war era, and was featured on aircraft such as the English Electric Canberra and the V-bomber fleet. It also saw civilian use, and a number of new Gee chains were set up to support military and civil aviation across Europe. The system started to be shut down in the late 1960s, with the last station going off the air in 1970. Gee also inspired the original LORAN ("Loran-A") system

The basic idea of radio-based hyperbolic navigation was well known in the 1930s, but the equipment needed to build it was not widely available at the time. The main problem involved the accurate determination of the difference in timing of two closely spaced signals, differences in milli- and micro-seconds.

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