The second half of the present century has witnessed the advent of intensified conflict of sea-use. The elements of this are well known: expanding international trade, carried in more numerous, often larger, and faster ships; the exploitation of oil and gas deposits under the sea bed; and always the fisheries, life-support of much of the still increasing population of the world.

The particular aspect of sea-use conflict which the establishment of Vessel Traffic Services (VTS) is intended to resolve is that arising from the concentration of shipping in the approaches to great ports, and in straits. The protagonists in this conflict are, on the one hand, any authority on shore which, with or without the sanction of international agreement, seeks to impose order upon the flow of vessel traffic, and on the other, the masters of vessels, each of whom is responsible ‘under God’ for the safe navigation of his ship. The pilot, as professional adviser to both the protagonists is now acquiring a new responsibility as ‘ honest broker’ between the ship master and the port authority. Indeed, it would accord with this role if the pilot were to be paid, in some proportion, by the port authority as well as by the shipowner. Be that as it may, since the establishment in 1948, at Liverpool, of the world's first port radar station, it could be said that experience has confirmed that by far the most important features of a Vessel Traffic Service are its radar coverage, which provides ‘the authority’ with an overview of all traffic in the area of responsibility; and the v.h.f. radio network for voice communication with the pilots, shipmasters, tugmasters and other individuals directly concerned with the operation of the port. It is a curious fact that, so far, there has been no concerted move to introduce the technological device required to enable the port operator to correlate an echo on his radar display with its corresponding identity and hence, radio call sign. It is the aim of this paper to compare the existing means of identification and recognition of radar contacts in a VTS with what is technically and economically feasible; to determine the operational requirement; and to set out the characteristics of a system which would meet the requirement.