One of the essentials of a high-speed sea-going vessel is high-powered machinery. A large portion of the interior of the pressure-resisting hull, therefore, must be devoted to machinery space. The quarters would necessarily be somewhat cramped without a buoyant superstructure, which gives plenty of room for the crew to take exercise and secure plenty of fresh air when off duty, even in rough water. As it is very important to keep the physical and mental condition of the crew in a satisfactory state, it is essential that the men be not kept in restricted quarters for a long period of time. This vessel is designed to carry torpedoes firing in line with the axes of the ship both fore and aft, and carries, also, torpedo tubes in the superstructure which may be trained to fire to either broadside. Of course, such a vessel as this should be fitted with wireless and sound-transmitting and detecting devices, and, to be effective, should have a speed of at least twenty-five knots, in which case she would be able to pursue and overtake any battle fleet that could be assembled from existing ships in any navy in the world. Undoubtedly such high-speed submarines will come into being within the next few years. Congress, in 1914, appropriated money to build "fleet submarines," in which they expressed the desire to secure twenty-five knots. A certain amount of discretion, however, was left with the Navy Department, which would permit them to accept boats of not less than twenty knots. There is no difficulty in the way of making such vessels function satisfactorily when submerged, but up to date no internal-combustion engine has been produced suitable for such high-speed submarines, and steam has many disadvantages in a military submarine, which should be able to emerge and get under way at full speed after a long period of submergence. The tactics of the fleet submarine would be to search for and destroy the enemy's warships or commerce carriers wherever they could be found. A seagoing submarine of such character would also carry rapid-fire guns of sufficient calibre to destroy surface merchantmen. Having sufficient speed to overhaul them, they would be able to capture the merchantmen and perhaps take them as prizes into their own ports, something which it is impossible for the commander of the small-sized submarines now in commission to do, as they have neither the speed to overhaul swift merchantmen nor guns of sufficient range and power to destroy them if they refuse to follow the instructions of the submarine commander. The only alternative, therefore, has been to destroy the merchantmen, and, in many cases, the crews and passengers of the merchant ships have been destroyed as well. This latter policy, however, is much to be regretted.