Submarine Appliances And Their Uses
Deep Sea Diving, &c., &c.

In Fig. 3 is shown a cylindrical case for a ground mine. There are two sizes of this mine in general use, i.e., 500 lbs. and 250 lbs. The inside of each case is provided with a lining of cement, which forms a charge chamber for the guncotton, and gives additional weight, tend- ing to prevent the mine from rolling about after having been placed in position. Cylindrical mines are also used as buoyant mines, chiefly for offensive purposes, and contain charges of cither 76 lbs. or 500 lbs. The 76 lbs. mine may be used either as an clcctro-contact mine to fire from shore, or as an elcctro-mechanical mine to be fired from a battery contained in the mine itself. This latter system is, however, objectionable, inasmuch that the mines are dangerous to prepare and lay out, and when laid are dangerous alike to friend and foe ; they should never be used except, perhaps, as offensive mines for such purposes as blockading an enemy’s port. The 500 lbs. mine is intended for use in offensive operations as a countermine, but may also be used as an observation mine to fire from the shore. The following is a brief description of the method of mooring the foregoing mines under the various conditions in which they are likely to be employed. Method of F ig- 4 shows a 500 lbs. buoyant mine moored under a circuit closer case. This Mine'”* method of mooring is resorted to when it is required to place large charges in deep water. The mine is moored to a cast-iron sinker, or anchor, by means of a steel wire mooring rope, and the circuit closer case is secured to the upper attachment chain of the mine sufficiently near the surface to be struck by a passing vessel. In moderate depths a smaller case, with a cement lining, would be used instead of the buoyant case; the mine would be at the bottom, as seen in Fig. 5, which shows a ground mine moored under a circuit closer case. If it be desired to defend a fairway through a defence with buoyant contact mines, these should be moored “Dormant,” i.e., kept moored close to their sinkers at the bottom in order to avoid injury by friendly traffic in time of peace, and arranged to rise to within striking distance of the surface when an attack is expected. Such a mine is shown in Fig. 6. The device for holding the mine down consists of a gripping box and exploding link con- taining a small explosive charge. The circuit is so arranged that this charge can be fired at will from the shore, thus breaking the link and allowing the mine to rise to the full extent of its mooring rope, (he length of which has been previously adjusted to ensure the mine floating at the required depth. Fig. 7 shows a cylindrical mine moored as a buoyant mine, and arranged to fire on contact with a hostile ship. This class of mine is usually arranged in groups, and may re- ceive the firing current either from the shore or from a submarine battery moored in the mine field in the centre of a group; or, to further economise cable, the battery can be contained in the mine itself, but, as before stated, this latter method is objectionable, and attended with danger to those employed in preparing and laying. Fig. 8 shows a line of countermines in the position they occupy when laid. Counter- Countermining is an operation carried out usually for the purpose of clearing a channel mining. through an enemy’s submarine defence for the passage of attacking vessels. It consists of dropping a number of mines, usually twelve, automatically from a specially prepared counter- mining launch. The 500 lbs. cylindrical buoyant mine is usually employed in this operation. 116