In this paper the history and development of inertial systems for the merchant marine is traced from the gyro-compass, familiar at sea since the beginning of the century, to complete inertia systems and integrated systems such as doppler/inertia.

The paper was presented at the Marine Navigation Symposium held in Sandefjord, Norway, on 24–6 September 1969 and is reproduced with the permission of the organizers.

The gyro-compass was first fitted on board a ship as long ago as 1908. Its function has been as the main reference by which the ship is steered and to which navigation by dead reckoning and direction finding is referred. The compass has been developed continuously to provide a more reliable, more accurate, and smaller instrument costing typically £1000 to £2000.