Editing Radio navigation (section)

===Bombing systems===
The first distance-based navigation system was the German [[Y-Gerät (navigation)|Y-Gerät]] blind-bombing system. This used a [[Lorenz beam]] for horizontal positioning, and a transponder for ranging. A ground-based system periodically sent out pulses which the airborne transponder returned. By measuring the total round-trip time on a radar's oscilloscope, the aircraft's range could be accurately determined even at very long ranges. An operator then relayed this information to the bomber crew over voice channels, and indicated when to drop the bombs.{{fact|date=July 2022}}

The British introduced similar systems, notably the [[Oboe (navigation)|Oboe]] system. This used two stations in England that operated on different frequencies and allowed the aircraft to be triangulated in space. To ease pilot workload only one of these was used for navigation – prior to the mission a circle was drawn over the target from one of the stations, and the aircraft was directed to fly along this circle on instructions from the ground operator. The second station was used, as in Y-Gerät, to time the bomb drop. Unlike Y-Gerät, Oboe was deliberately built to offer very high accuracy, as good as 35&nbsp;m, much better than even the best optical [[bombsight]]s.{{fact|date=July 2022}}

One problem with Oboe was that it allowed only one aircraft to be guided at a time. This was addressed in the later [[Gee-H (navigation)|Gee-H]] system by placing the transponder on the ground and broadcaster in the aircraft. The signals were then examined on existing [[Gee (navigation)|Gee]] display units in the aircraft (see below). Gee-H did not offer the accuracy of Oboe, but could be used by as many as 90 aircraft at once. This basic concept has formed the basis of most distance measuring navigation systems to this day.{{fact|date=July 2022}}