Abstract: An aircraft navigation system is disclosed for use in missions involving unfamiliar terrain and/or terrain having hostile forces. The navigation system includes an inertial navigation system, a map of the terrain with elevational information stored in a digitized format as function of location, a typical energy managed or narrow (radar or laser) beam altimeter, a display system, and a central processing unit for processing data according to preselected programs. The data processing system includes an operational mode (software program) for relating the continuing sequence of altimeter readings with the changing aircraft position on the digitized map. In this manner, the true position of the aircraft can be determined with respect to the digitized map and can be displayed on a plan view of the map. When the correct position of the aircraft with respect to the digitized map is known, a display of the map and the aircraft can provide presentations useful to the navigation of the aircraft, e.g.