A direct indication of distance to known geographical points has long been a requirement for aerial navigation. The system described in this paper consists of an airborne light-weight radar set which works in conjunction with a responder beacon on the ground. The aircraft radar transmitter sends out a stream of pulses which are returned on a slightly different radio frequency by the ground beacon. Automatic circuits in the aircraft set measure the interval between the outgoing and corresponding return pulses and present the information to the pilot on a meter calibrated in miles.The paper describes the design of the airborne set and the results obtained in airline trials of engineered equipment used on an air route.