ONE of the earliest applications of radio wave transmission was the introduction of a service whereby ships could be informed of their position under conditions in which ordinary visual observations or dead reckoning were not very reliable. For many years past, radio direct ion-finding stations on shore have supplied bearings to ships making special signals for the purpose ; while many forms of direction-finder suitable for installation in ships have also been available, and could be used for observing the bearings of fixed radio beacons, which can easily be identified by the simple code signals emitted at regular intervals. During the past seven years, the growth and development of radio technique has been so rapid and so extensive that not only has a great deal of advance been made in the field of radio direct ion -finding as such, but also there has been devised and developed a number of alternative systems of using radio waves for fixing the position of a ship, whether it be in the open sea, near a coast or approaching a harbour. There are, in fact, so many possible systems of radio aids to marine navigation that it has become quite a difficult problem to decide which are the best or most appropriate for various applications. In order to reduce the number and variety of equipments to be carried by ships navigating in various parts of the world, it is clearly desirable that there should be some measure of international agreement on the matter.