The navigator at the present time relies greatly on both optical devices and on radio systems utilizing electromagnetic waves ranging in wavelength from millimetres up to hundreds of metres. The laser extends the coherent properties of radio waves into the visible part of the spectrum. It is natural therefore to expect that this increased facility should lead to the possibility of devising systems based on the laser which might help to overcome problems that still exist in navigation.

It is the purpose of this paper to describe the principles and performance of present-day lasers, to survey some of the techniques used in navigation in order to discover those in which the laser might conceivably play a useful part, and to comment on the laser's advantages and disadvantages in comparison with existing methods. Finally, a particular form of laser called the ‘ring laser’ is described and discussed in some detail. The ring laser is of great interest in that it provides a completely novel way of measuring direction relative to inertial space, and is therefore a possible competitor to the gyroscope for inertial navigation. The ring laser can also measure the velocity of a transparent medium moving relative to it, which could be of use in determining vehicle velocity.