Abstract: An acoustic navigation system for marking channels is utilized for provid safe entry and exit from harbors. The system has a plurality of pairs of acoustic projectors aligned on opposite sides of a channel. Each pair is spaced from corresponding pairs, a predetermined distance along the sides of the channel. A first projector in each pair provides an acoustic source for a period of time. The other projector in the pair provides acoustic sources spaced at predetermined intervals both before and after the signal from the first projector. A vessel equipped with receiving and display equipment determines its own location within the channel from the received acoustic signals.