Abstract: In a head-up display system video signals derived by a television (or infra-red) camera which is mounted on the aircraft nose to view substantially the same scene as viewed by the pilot along his line-of-sight through the partially-transparent reflector of the head-up display system, are mixed with the video signals which are supplied by a waveform generator in accordance with aircraft-attitude and weapon-aiming symbology that is used for projection onto the reflector. The combined signals, representing the external scene with the symbology superimposed, are supplied to a video-tape recorder for subsequent, or immediate, replay by a television monitor in the aircraft or via the pilot's head-up display unit, and are also supplied to a transmitter to enable recording and display to be carried out at a ground station.