When radar is used at sea as an aid to collision avoidance, the necessary information has to be obtained by maintaining a plot, which, however, can only offer the average course and speed over a passed time. It is not a reliable prediction of future actions, so that to make too long an extrapolation from a plot is hazardous. It might in some circumstances be better if a ship could be called up by radio and asked her intentions, though this requires first a knowledge of her identity and call sign.

This paper outlines a system of communication that would make it possible to call a ship (fitted with the necessary receiving equipment) initially located only by range and bearing, to obtain the identity of the ship and establish courses, speed and intended actions, and if necessary, radio call signs and calling frequencies. The messages passed by a ship would be recorded automatically. It is proposed that the system should have an operating range of 15 miles, though this does not represent a limit to the range possible. There are objections perhaps to trying to get out of a mutilateral situation of danger by bilateral agreements, and at least one school of thought would hold that the danger is likely to be increased by relying on communication. Nevertheless the system described here holds considerable interest and might, as the author suggests, serve other purposes at sea.