For purposes of coast defence the submarine may be said to have fairly established its value. The knowledge that such craft were “in being” would have a deterrent influence upon an admiral attacking a fort or contemplating a blockade, and in all probability the days of close blockade are over. As a weapon of offence the utility of the submarine boat is not so clearly established. It is true that some of the French boats have operated at a considerable distance from their base, but its speed, its seaworthiness, and range of action must be improved before the submarine can be regarded as a useful adjunct to a fleet acting on the offensive. The radius of action at the surface of the newest _Hollands_ is only 400 knots at 8 knots per hour, and submerged the speed is 7 knots for a four hours’ run. [Illustration: THE “FULTON” RUNNING ON THE SURFACE. ] Still even now there are uses to which a submarine boat might be put, such, for instance, as the attack of ships shut up in a blockaded harbour, or of vessels in port; the destruction of a mine field so that ships may enter in safety; the cutting and repairing of cables; the forcing an entrance through a boom, &c. The late Captain Cairnes, in his book “The Coming Waterloo,” enunciated the theory that even if the British fleet destroyed the French fleet it would still be necessary for us to land an army on French soil in order to bring hostilities to a conclusion. In that case submarine boats would probably be employed, for some of the purposes above enumerated. It has been suggested that small diving torpedo-boats might be carried on battleships, and it is said that the United States have been experimenting with vessels of this kind. The difficulties of hoisting such vessels in and out of a big ship are, however, considerable, and few naval officers favour this idea. Perhaps a special “submarine depot ship” somewhat similar to the _Vulcan_ might be useful for conveying submarines to foreign waters.