Suppose, now, it is necessary to come to the top of the water at once, without waiting for the diving-rudders to steer us up. The compressed-air tanks can expel nearly twenty tons of water from the tanks at the bottom of the vessel in about two minutes, and the boat will rush to the top at once. Here is where the matter of buoyancy comes in. A problem that has also been solved in this boat is the ability to remain stationary at a certain depth under water. There is an anchor which is run from a drum at the bottom of the boat near the bow, and it will hold the boat in any position independent of current or tide. If it is desirable to remain in one position, and not at anchor, we must use two little "down-haul" screws. They are little screws such as propel a ship at the stern. An electric dynamo is set going, and these screws are turned in a horizontal position, and the small reserve buoyancy in the boat, amounting only to about 375 pounds, is overcome. When we are running under water the slight dip of the diving-rudders keeps us at the required depth.
RAMMING A MAN-OF-WAR.
There have been several devices to make a vessel go under water. The oldest, perhaps, has been the sudden filling of tanks by allowing the water to rush in. The water has to be expelled by air pressure. This method of diving and coming up consists of a series of bumping motions, and is very crude. Another method used was by "down-haul" screws. These were turned, and they simply bored holes in the water, like an auger in a board, and the boat had to go down in the water. After the boat got down there was no satisfactory way of regulating the depth, and the rise to the surface was always too abrupt. Propelling the boats under water until recently has been an unsolved problem. Sometimes chemicals have been used, and sometimes the stored-up heat of the engine has been tried. Electricity has solved this problem, and made it possible to stay under water six hours going at full speed. During this time the boat can go fully fifty miles without once coming to the surface. Should any accident occur, each member of the crew is supplied with a life-saving helmet, which is easy of adjustment, and by means of which he may float to the surface of the water in safety. A folding rubber boat may also be carried in the super-structure of the craft, so that there is very little danger of loss of life under the water. Mr. Holland has explored all New York Harbor, and he says that ladies have often asked him to take them down in his experimental boats.
The facility with which this vessel will do its work may be judged from the fact that when running on the surface of the water it can dive to a depth of twenty-five feet in twenty seconds. When running awash it can dive to a depth of twenty-five feet in ten seconds. It can come up as quickly as it goes down. It is supposed that the vessel will never need to go any deeper than forty feet, and having the ability to dive when attacked it will carry no guns.
Mr. Holland was a young man in Ireland during our civil war. He studied engineering, and was especially interested in the submarine boat that the Confederates used with considerable success, but with great loss of life to themselves, in the war. The splendid ship Housatonic of our navy was sunk off Charleston, South Carolina, by one of these boats. Mr. Holland came here in 1873, and two years later made his first experiment in going under water. He has kept at it ever since, and more than once has he given the pilots and skippers of New York Harbor a scare by suddenly causing to come to the top of the water some sort of a sea monster, the like of which no one ever dreamed, and the appearance of which could not be explained. One of Mr. Holland's boats was popularly known as the "Fenian ram," because he was practising in it in New York Harbor about the time of the celebrated Fenian uprising. He has lost one or two boats by the mistakes of some of his helpers, and on more than one occasion he has been in a ticklish situation, but he always came out all right, and finally mastered all the intricate problems connected with submarine navigation—problems that have engaged scores of men ever since Drebbell, a Dutchman, first tried the experiment in the time of James I. of England.
The first partly successful boat of this kind seems to have been made in the time of our revolutionary war by a man named Bushnell, who lived in Maine. The boat could remain under water for half an hour, but the scheme of building them came to nothing. It will surprise most persons, probably, to know that the first really successful boat was made by our own Robert Fulton, the famous steamboat engineer. It was in 1800, and Fulton showed it to Napoleon Bonaparte in the harbor of Havre in 1801. He went down twenty-five feet in it, and remained there for one hour. Then he went down with four persons, and remained four hours. Compressed air was used for respiration in this boat. Various improvements have been made from that time to this. The crude boats of the civil war were displaced in the late seventies and eighties by those of fairly satisfactory working arrangements, and the Russian, French, and Turkish governments have built several, but they have lacked complete mastery of the problem of under-water navigation, such as this boat that we are now building is expected to display. By next summer the boat will probably be in service.
If the boat is successful it may make as great a revolution in naval warfare as the famous Monitor, built by Mr. Ericsson, did in the war of 1861. For what battle-ship would be proof against it? The biggest of all battle-ships would only sink quicker than smaller ones, and huge war-ships of all kinds would be nothing more than death-traps for all those aboard them. Another question of great importance is whether the guns of war-ships can be tipped sufficiently to strike the boat when it is anywhere near.