The paper comments on the general requirements which should be met by designers of marine radar equipments. It suggests that in planning a new design the minimum standard of reliability that should be set is 500 hours mean time between failures. Some basic design precautions are then described covering various aspects of the problem from initial design and selection of components to installation, environmental and operational conditions. Short notes on maintenance and training aspects are also included. The paper concludes with an example of the extremely high reliability achievable by the use of a twin inter-switchable radar system wherein the probability of trouble-free operation over a specified period can be raised from 95.3% to 99.8%