by gun-fire before they are able to dive, or, with luck, may even be rammed. Destroyers, too, may be used to attack at night as torpedo-boats, or even in the course of a naval action if a favourable opportunity offers; it will be remembered that the _Goliath_ was torpedoed by a Turkish destroyer. "Vessels of stealth", as submarines have been called, have now taken the place of the obsolete torpedo-boat. The latter relied on torpedoing her enemy under cover of the darkness, but the submarine is most dangerous in day-time. At night it is almost impossible for her to find her target or to estimate the speed at which she is travelling if under way, without which knowledge it is extremely difficult to arrange for a torpedo to intercept her course unless fired at very close quarters indeed. As the particulars of our submarines are wisely kept secret, no more can be said about them than is already public property. The "E" class, our latest improved "Hollands", are 176 feet long, with a beam of a little over 22 feet, and have a displacement--when submerged--of 800 tons. When at the surface their heavy oil-engines, of something like 2000 horse-power, enable them to travel at a speed of from 16 to 20 knots. When under water the electric engines are brought into play, but owing to the increased friction and larger area of the vessel to be forced through the water the speed of the boat drops to 10 knots. Moreover, travelling at the most economical rate of speed, not more than 140 knots can be negotiated when submerged, while at the surface an "E" submarine can travel for no less than 5000 miles without refilling her oil-tanks.