The effect of radar on the application of the Rule of the Road at Sea has been given attention in several papers and discussions in recent months. Deductions on their relationship have been attempted, and already judgements have been delivered in the courts of this and other countries which take account of the installation of radar in one or both of the parties to a collision. The suggestion has been seen that guidance to mariners concerning their actions and responsibilities when radar is fitted must await the development of case law. This development will be a lengthy and probably painful process and the object of this paper is to discuss the possibility of establishing principles which would enable the great potential value and legitimate application of radar to be established without waiting for casualties.