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.
This quality results from the fact that each end of the boat forms a tank, which is filled with water, and as there is no extra buoyancy in those directions, and consequently no tendency to lift at those parts as with an ordinary vessel in a sea-way, the vessel rises and falls bodily instead of pitching. It has been found that by going at a moderate speed and taking the seas a point or so on the bows the boat makes very good weather, as the waves, breaking on the snout, sweep over the fore part and expend their force before any portion of them can reach the central section.