The prime purpose of the navigation system in a combat aircraft is to determine the relative positions of aircraft and target with sufficient accuracy to enable a weapon to be released. In practice the actual system installed in the aircraft is a compromise solution, which depends on three factors, namely, the mission to be flown, the type of aircraft and the navigation phases through which the aircraft flies while performing the mission. Broadly speaking there are two types of navigation phase; these will be termed macronavigation and micronavigation. Macronavigation is concerned with the navigation of an aircraft to some pre-determined point on the Earth's surface while micronavigation is the final, highly accurate navigation phase required for weapon release. Micronavigation can be further sub-divided into static and dynamic micronavigation; static when the target and the coordinate system within which it exists are fixed, and dynamic when the target moves within a coordinate system which is defined by the attacking aircraft.