Optical identification friend-or-foe

An identification friend-or-foe system for vehicles comprising, in each vehicle, a narrow-beam radiation transmitter and a receiver with a panoramic detection means for detecting radiation transmitted by other vehicles from any direction around the horizon, the transmitter having a means for transmitting a first coded signal, and the receiver comprising a reflector, blocking means, having a blocking mode in which said blocking means completely encircles said reflector, for, in said blocking mode, blocking transmission to said reflector, and means for detecting and identifying the first coded signal transmitted by other vehicles and for, responsive thereto, providing an unblocking signal to the blocking means so as to clear a radiation transmission path completely around the reflector so that the reflector reflects a received signal received from any direction around the horizon after a predetermined code is identified and the transmission path is cleared responsive to said unblocking signal, the reflector comprising a continuously rotating retroreflector that reflects a signal received from any direction around the horizon back in that direction and said retroreflector including means for adding a further predetermined code to a signal reflected from said retroreflector, each vehicle including a further means directed in the same direction as the radiation transmitter for detecting a reflected signal.