individual aircraft, Oboe was used both to guide marker aircraft for the Main Force and for bombing aircraft making precision bombings of high value targets. It was by far the most accurate bombing system used during the war. History Background In order to accurately determine your location relative to objects on the ground you need two data points; two angles (as in triangulation), two distances (trilateration), or an angle and a distance (VOR/DME). Using radio to provide some or all of these measurements was an area of continual development leading up to the start of the war. The Germans pioneered this approach with operational systems like Lorenz beam and X-Gerät that used two narrow beam-like signals that crossed at a point in the sky to indicate a target using triangulation. Later, during The Blitz, the Germans introduced Y-Gerät, which combined a single Lorenz beam with a transponder-based distance measurement to fix locations. The problem with all of these systems was that they produced no information except within their narrow beams, and were not useful for general purpose navigation. A more useful system was introduced in the RAF's Gee system, which used two timed signals that allowed the navigator on the bomber to determine their location using trilateration. It could be used anywhere within line-of-sight of the transmitter stations in the UK, and generally provided a reasonable signal up to about , depending on the aircraft's altitude. Gee was read on an oscilloscope display about across, which limited the accuracy of the timing measurements. As a result, Gee was accurate on the order of kilometers, which was extremely useful for navigation and area bombing, but did not provide the accuracy needed for pinpoint bombing. As the accuracy of Gee was largely due to the mechanical size of the indicator unit, the accuracy could be improved by using a larger display. However, in these early days of the cathode ray tube (CRT), such displays were extremely expensive and very long, which made them unsuitable for fitting to a large number of Bomber Command aircraft. Initial proposal The concept of reversing the display arrangement so the display could be on the ground and the transmitter on the aircraft was obvious. It had first been suggested by Alec Reeves of Standard Telephones and Cables in 1940 and then formally presented with the help of Francis Jones in the spring of 1941. The basic idea