THE GEE SYSTEM
<< Appendix A
Prior to the introduction of Gee, navigation in Bomber Command had been based largely on dead reckoning, assisted by drift-taking and by three methods of position finding—visual pinpointing, radio loop bearings and astro. All three methods were subject to very considerable error, as indicated by scientific analysis and proved by the examination of photographs. The basis of the Gee system was a wireless pulse signal transmitted simultaneously by two stations, a "master" and a "slave*1 station, and displayed on a cathode ray tube in the aircraft. By measuring the difference in time between the reception of the two signals, and by keeping this difference constant, it was possible to keep the aircraft on a pre-determined line— the line of constant difference between the two stations. Further, by means of a second pair of transmissions from the same "master" and a different "slave" station, an exact point on the line could be determined, with the help of specially prepared charts. For blind bombing and homing, the operator could reverse the process and set up his equipment in advance, directing the pilot to steer the aircraft so that when the pulses intersected the plane would be over the pre-selected position.