Whilst the torpedoists of the extreme school claim that torpedo vessels can attack with a very good chance of success in daylight, the more general opinion is that they will he utilised chiefly under cover of darkness, and that the destroyer and the smaller torpedo-boat would stand no chance in broad daylight against the tremendous artillery fire to which they would be subjected by the battleships singled out for attack. Even at night, however, the flare from her funnels might betray the destroyer. A writer in the _United Service Gazette_ a few years ago remarked that the development of quick-firing guns brought about by the increase in the offensive and defensive power of swift torpedo-boats threatened ere long to completely abolish the use of surface torpedo-boats in marine warfare unless the latter could be rendered proof against those terribly destructive weapons, the new rapid-firing guns of large calibre. To secure this invulnerability by the aid of armour would destroy the speed and hardiness of the torpedo-boats, and it had long been the opinion amongst naval officers, more especially on the Continent and in America, that if the torpedo is to be used for successful attack it would have to be discharged from a vessel which was rendered invulnerable by being totally submerged—that is to say, from a submarine torpedo-boat. The submarine boat of the future will be a diving torpedo-boat capable of manœuvring (1) on the surface, (2) awash with conning tower only above the water, and (3) beneath the waves. It will have two methods of propulsion, one for the surface, one for beneath the water, and its mode of operation will be to steam on the surface until it is within sighting range; to then take in enough water ballast to bring it to the “awash” condition, thus greatly reducing the chances of being hit; and, having approached within a certain distance of the enemy, to sink entirely beneath the waves, rising once probably for a second to take final bearings before firing its torpedo. The nine vessels ordered for our navy are really diving torpedo-boats and are not intended for use under water except for very short intervals of time. The submarine of to-day bears a close resemblance to the torpedo-boat in the early stages of its development and appears to be of more value to a country that is desirous of defending its coasts than to one which must maintain the command of the seas. There are signs, however, that in the process of its evolution the submarine will go through many of the same stages as did the torpedo vessel, and will develop into an offensive weapon which England will be unable any longer to despise. That a _Holland_, a _Narval_, or a _Gustave Zédé_ is as formidable an adversary as an _Albatross_ or an _Express_ few would claim, but the last word has not yet been said on submarine navigation, and the future may be expected to bring about many changes.