For harbour defence and the safety of the battle-ship the wire-guided and propelled torpedo will form a second line behind the fast torpedo-boat. This type of weapon strikes with more unerring accuracy than any other yet included in the armoury of naval warfare, because it is under the control of the marksman from the time of its launching until it fulfils its deadly mission. Its range, of course, is strictly limited; but it may be worked to advantage within the distances at which the best naval artillery can be depended upon to make good practice.
The least costly and the lightest form is that in which the backward pulling of two wires, unwinding two drums on the torpedo, actuates two screws at greater or less speeds according to the rapidity of the motion imparted, any advantage of speed in one screw over the other being responded to by an alteration in the direction taken by the weapon. The torpedo may be set so as to dive from the surface at any desired interval; but, of course, an appearance in the form of at least a flash is necessary to enable the operator to judge in what direction he is sending his missile. Small torpedo-boats, not manned but sticking to the surface, may be used in the same manner. Each one no doubt runs a very great risk of being hit by shot or shell aimed at them; but out of half a dozen, discharged at short intervals, it would be practically impossible for an enemy to make certain that one at least did not find its billet.
The submarine boat will have some useful applications in peace; but its range of utility in warfare is likely to be very limited. It is hopeless to expect the eyes of sailors to see any great distance under the water; therefore the descent must be made within sight of the enemy, who has only to surround himself with placed contact-torpedoes hanging to a depth, and to pollute the water in order to render the assault an absolutely desperate enterprise.
Military aeronautics, like submarine operations in naval warfare, have been somewhat overrated. Visions of air-ships hovering over a doomed city and devastating it with missiles dropped from above are mere fairy tales. Indeed the whole subject of aeronautics as an element in future human progress has excited far more attention than its intrinsic merits deserve.
A balloon is at the mercy of the wind and must remain so, while a true flying machine, which supports itself in the air by the operation of fans or similar devices, may be interesting as a toy, but cannot have much economical importance for the future. When man has the solid earth upon which to conduct his traffic, without the necessity of overcoming the force of gravitation by costly power, he would be foolish in the extreme to attempt to abandon the advantage which this gives him, and to commit himself to such an element as the air, in which the power required to lift himself and his goods would be immeasurably greater than that needed to transport them from place to place.
The amount of misdirected ingenuity that has been expended on these two problems of submarine and aerial navigation during the nineteenth century will offer one of the most curious and interesting studies to the future historian of technological progress. Unfortunately that faculty of the constructive imagination upon which inventive talent depends may too frequently be indulged by its possessor without any serious reference to the question of utility. Fancy paints a picture in which the inventor appears disporting himself at unheard-of depths below the surface of the sea or at extraordinary heights above the level of the land, while his friends, his rivals, and all manner of men and women besides, gaze with amazement! Patent agents are only too well aware how often an inordinate desire for self-glorification goes along with real inventive talent, and how many of the brotherhood of inventors make light of the losses which may be inflicted upon trusting investors so long as they themselves may get well talked about.
Nations may at times be infected with this unpractical vainglory of inventiveness; and on these occasions there is need of all the restraining influence of the hard-headed business man to prevent the waste of enormous sums of money. The idea that military ascendency in the future is to be secured by the ability to fly through the air and to dive for long distances under the water has taken possession of certain sections in France, Germany, Russia, Great Britain and the United States. Large numbers of voluble "Boulevardiers" in Paris have, during the last years of the nineteenth century, made it an article of their patriotic faith that the future success of the French navy depends upon the submarine boat. The question as to what an enemy would do with such a boat in actual warfare seems hardly ever to occur to them; and, indeed, any one who should venture to put such a query would run the risk of being set down as a traitor to his country!
More important to the student of the practical details of naval preparation is the great question as to the point at which the contest between shot and armour will be brought to a standstill. That it cannot proceed indefinitely may be confidently taken for granted. The plate-makers thicken their armour while the gun-makers enlarge the size and increase the penetrative power of their weapons, until the weight that has to be carried on a battle-ship renders the attainment of speed practically impossible.
Meanwhile there is going forward, in the hull of the vessel itself, a gradual course of evolution which will eventually place the policy of increasing strength of armour and of guns at a discount. The division of the air-space of a warship into water-tight compartments will doubtless prove to be, in actual naval conflict, a more effectual means of keeping the vessel afloat than the indefinite increase in the thickness and consequent weight of her armour.
The most advanced naval architects of modern times are bestowing more and more attention upon this feature, as affording a prospect of rendering ships unsinkable, whether through accidents or through injury in warfare. No doubt, for merchant steamers, it will be seen that development along the lines already laid down in this department will suffice for all practical purposes. The water-tight bulkheads, with readily closed or automatically shutting doorways, ensure the maintenance of buoyancy in case of any ordinary accident from collision or grounding, while the duplication of engines, shafts and propellers—without which no steamship of the middle twentieth century will be passed by marine surveyors as fit for carrying passengers on long ocean voyages—will make provision against all excepting the most extremely improbable mishaps to the machinery.