Conventional survey methods for position and azimuth as practised in the Royal Artillery, although sufficiently accurate, were slow and expensive in manpower, while vehicle-navigation systems based on distance measurement by odometer and directional gyros were not sufficiently accurate. In the early 1970s therefore a General Staff Requirement was issued for an equipment designated PADS (Position and Azimuth Determining System) which would provide the necessary combination of speed and accuracy for gun batteries and observation posts, which may have to move frequently, by day or by night, in poor visibility. Precise knowledge of battery and target location, together with an azimuth reference, can help to achieve the first-salvo hit capability that is essential, not only from the point of view of surprise, but also to reduce risk of detection by shell-locating radar.