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MINE-SWEEPING. Almost immediately upon the development of the mine itself came the development of measures for combating of mines. From the very first the mine was used as a weapon of offense and it became necessary to find some means of protection against it. As early as 1777, Bushnell, an American inventor, devised moving machines which were dis charged in the Delaware River against British ships. These were later ridiculed in a ballad called

During the American Civil War, however, mines began to be used on so large a scale and so effectively that it became necessary for the Northern States to adopt adequate measures for protection against them. The first idea was to creep for the cable connecting the torpedoes, in the hope that the creep would break the cable or explode the mines. Later, chains towed between two vessels were used in an attempt to scizze the moorings of the mines, the latter being then raised and rendered harmless. These methods do not appear to have met with any great measure of success.

In 1863, Ericsson constructed his mine-de stroyer, which consisted mainly of a strong float attached to the forward part of the ship and extending well to the front of the bow. At the extreme front end of the float and sev eral meters under the surface of the water was fixed an explosive charge of 700 pounds of powder. In front of the charge were rigged two timbers which, upon engaging an obstacle, closed upon each other as do the parts of a parallel ruler, thereby igniting the charge. The important feature of the invention was the air chamber placed directly in front of the charge. This gave way at the push of the explosion and allowed the full foce to be sent forward against the obstacle, thereby protecting the float itsself from any damage. A large number of these mine-catchers were produced at that time, but for some reason or other no further use was made of the invention.

Up to quite recent times nothing had been done toward the improvement of methods for the detection of mines. They had been used mostly as a weapon of defense for the protec tion of coastal localities and the blocking of channels, until the outbreak of the Russo-Jap anese War. During this war, however, it be

came the custom to strew broadcast great num bers of unanchored mines, and it became neces sary to find a means of searching out the loca tion of these mines and destroying them.

The oldest method of protecting warships against mines was in the use of less valuable ships as exploders. One or more of these would go ahead of the battleships, in the hope of strik ing and exploding enough mines to make a breach in the minefield. The exploder had to he of draught at least equal to that of the ship to be protected, and also had to be so constructed that after the explosion of the first mine the engines would still drive it ahead to the destruction of others. To meet the latter requirement, the ship had to have its engines located aft, as in the case in tank steamers. Of course, the exploder was inevitably sacri ficed, so that the method was a very expensive one. Other objections were that even a num ber of these ships might go through a field and miss mines that would sink the ships to be pro tected, and that success in the exploder's mis sion meant sure death to her crew, Another contrivance for the discovery of and protection against mines is the mine-catcher. This is a very heavy and clumsy apparatus, consisting of steel frames or wooden balks fixed to the sides of the vessel, supported and stiff ened below by wire hawsers. The mine-catcher is expected to break the moorings, causing the mine to rise to the surface, where it can be rendered harmless, or to overturn the mine, causing the explosive to be displaced. In any case, it is quite likely that the resulting explo sion will damage the catcher, necessitating fre quent repair. In order to be able to break a wire hawser, the mine-catcher has to be very strongly constructed. This results in a bulk and weight which greatly hinder the proper navigation of the ship and hold it down to a very slow pace. Counter-mines are often used although they are in reality not employed to seek out the location of mines, hut rather to destroy a field which has already been located. They are joined up in a series and towed along on a wide front. When it is found that the counter-mines have engaged the enemy mines, the boats sheer off the necessary distance and the charges are exploded by electricity, the nearby enemy mines being thereby destroyed.

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