Any discussion on the navigational problems of hovercraft must obviously be closely associated with the control characteristics of the craft. Although these machines have been widely publicized as capable of operating over almost any terrain which is reasonably flat, it will be assumed that the present discussion is concerned primarily with operation over water.

The word hovercraft may be regarded as a generic term in the same category as aircraft, ship, motor vehicle &c., and practical examples are likely to take a variety of forms depending upon their particular application. Thus, the control characteristics and the way in which they affect the navigational problem are likely to vary, in degree at least, amongst the different types. Again, it must be realized that the hovercraft as a transport system is only at the beginning of a long development phase, and any remarks of a general nature which are made at this time must be read in that context. Even at this early stage, however, two distinct applications of the hovercraft principle, as applied to over-water transport machines, have emerged and it is important to appreciate the difference between them.