If the numerical estimate of the chance of the disablement of a single engine and its propeller during a certain voyage be stated at one to a thousand, then the risk of helplessness through the break down of both systems in a vessel having twin screws and entirely separate engines will be represented by the proportion of one to a million. This mode of reckoning, of course, assumes that the two systems could be made absolutely independent in relation to all possible disasters; and some deduction must be made on account of the impossibility of attaining this ideal. Yet it is evident that when every practicable device has been adopted for rendering a double accident improbable the chances against such a disaster will not be far from the proportion stated.
When we come to consider the evolution of the warship as compared with that of the merchant steamer, we are at once confronted with the fact that the infliction of injury upon the boilers, the engine, or the propellers of a hostile vessel is the great object aimed at by the gunners. The evolution of the warship in the direction of ensuring safety, therefore, will not stop at the duplication of the engines, boilers and propellers. In fact it must sooner or later be apparent that the interests of a great naval power demand the working out of a type of warlike craft that shall be almost entirely destitute of armour, but constructed on such a principle—both as to hull and machinery—that she can be raked fore and aft, and shot through in all directions without becoming either water-logged or deprived of her motive power.
A torpedo-boat built on this system may consist essentially of a series of steel tubes of large section grouped longitudinally, and divided into compartments like those of a bamboo cane. Each of these has its own small but powerful boilers and engines, and each its separate propeller at the stern. Care also is taken to place the machinery of each tube in such a position that no two are abreast. In fact, the principle of construction is such as to render just as remote as may be the possibility of any shot passing through the vessel and disabling two at the same time.
If a boat of this description has each tube furnished not only with a separate screw at the stern, but also with a torpedo at the bows, it can offer a most serious menace to even the most powerful battle-ship afloat, because its power of "getting home" with a missile depends not upon its protective precautions, but upon an appeal to the law of averages, which makes it practically impossible for any gunners, however skilful, to disable all its independent sections during the run from long range to torpedo-striking distance. The attacked warship is like an animal exposed to the onslaught of one of those fabled reptiles possessing a separate life and a separate sting in each of its myriad sections; so that what would be a mortal injury to a creature having its vital organs concentrated in one spot produces only the most limited effect in diminishing its strength and powers of offence.
Or this class of naval fighter may be regarded as a combined fleet of small torpedo-boats, bound together for mutual purposes of offence and defence. Singly, they would present defects of coal-carrying capacity, sea-going qualities, and accommodation for crew which would render them comparatively helpless and innocuous; but in combination they possess all the travelling capacities of a large warship, conjoined with the deadly powers at close quarters of a number of torpedo boats, all acting closely in concert upon a single plan.
The chief naval lesson taught during the Spanish-American War was the need for improving the sea-going qualities of the torpedo-boat before it can be regarded as a truly effective weapon in naval warfare. It was announced at one stage that if the Spanish torpedo-boat fleet could have been coaled and re-coaled at the Azores, and two or three other points on the passage across to America, it might have been brought within striking distance of the United States cruisers operating against Santiago. This hypothetical statement provided but cold comfort for the Spaniards, who had been persuaded to put so much of their available naval strength into a type of craft utterly unsuited for operations complying with the first great requirement of naval warfare, namely, that the proper limit of the campaign coincides with the shores of the enemy's country.
But when the naval architect and the engineer have evolved a class of torpedo-using vessel which can both travel far and strike hard, and which, moreover, can stand a few well-directed shots penetrating her without succumbing to their effect, a new era will have been opened up in naval warfare—an era of high explosive weapons requiring to strike home with dash and bravery in spite of risk from shot and shell; but, like the bayonet on land, capable of overthrowing all war-machines which can only strike from a considerable distance.