The advent of true-motion radar has been a great step forward in the problem of allowing a ship to operate safely in congested waterways. Harbour radar, however, is still a requirement for two reasons; first of all it can well provide far more immediate information than is available from true-motion radar. Fig. 1 emphasizes this by showing how much additional information can only be available directly from a static site. Consequently it allows shore authorities to be advised of what is happening in conditions of bad visibility where they would otherwise be devoid of most information. This raises the problem of how the information is to be used.