The introduction of marine radar into the general market immediately after the last world war, offered the promise of reducing the many economic losses sustained through failure to keep schedules during periods of reduced visibility. These promises have been only partially fulfilled. Initially it was accepted that radar needed little introduction—that it established the range and bearing of targets in the vicinity and no more was required. With radar available on only a small proportion of vessels, this limited information was sufficient to enable these few to avoid other, slower-moving craft which were not so fitted. Radar is now fitted on almost all vessels and speeds have increased, while manoeuvring characteristics have changed because of increased tonnage of vessels. The situation is now far more complex.