1. Submarine boats have been built in which several persons have descended (with safety) for a great distance below the surface of the water. 2. Submarine boats have been propelled on and under the surface in all directions. 3. The problem of supplying the necessary amount of respirable air for a crew of several persons for a number of hours has been solved. 4. Steam, compressed air, and electricity have been used as the motive power. 5. The incandescent electric light has been used for illuminating the interior of submarine boats. 6. Seeing apparatus have been made by which the pilot, while under water, may scan the horizon in all directions. 7. A vessel has been in time of war destroyed by a submarine boat. The latter, it is true, was also sunk, but it was for reasons that are no longer in force. As yet no perfectly successful boat of this type has been tried in any naval war, but there is no question that they will be used at the very first opportunity. Compared with a surface boat, the submarine has the following advantages: 1. It does not need so much speed. The surface boat demands this quality so as to get quickly within striking range of its torpedo, and then to escape speedily out of range of machine guns, etc. 2. Its submersion in the presence of the enemy prevents the engines being heard. 3. There is no smoke nor glare from the fires to cause its detection. 4. The boat and crew, being under water, are protected from the fire of machine guns and rifles. 5. It is enabled to approach the enemy near enough to make effective even an uncontrollable fish torpedo. 6. It can be used with safety as a reconnoitring or despatch-boat. 7. It can examine the faults in the lines of submarine mines, and replace mines exploded in action. Abroad, the Nordenfeldt boat has awakened the most interest, and here the American submarine monitor holds the first place. The form of the Nordenfeldt boat is that of a cigar or of an elongated cylinder tapering away to a fine point at each end. The outer case, built of stout steel, is calculated in its construction to resist such a pressure as would enable the boat to descend even beyond a depth of fifty feet, although that is set as the maximum for its diving operations. The cigar shape does not at first sight commend itself, even in the eyes of nautical men, on account of its supposed tendency towards a rolling motion. The experience, however, gained with the boat exhibited for the benefit of naval experts at Carlscrona, in September, 1885, has shown that very good sea-going qualities can be developed in a craft built upon such lines; for this small vessel has weathered more than one gale in the Baltic, to say nothing of the severe storm it encountered at the entrance to the Kattegat when proceeding from Gottenburg to Copenhagen for the experimental trials.