Shells for a 15-in. gun are usually about 10 ft. long over all. the body being about 7 ft. and the rear extension 3 ft. These have a total weight, when filled. of 1,000 lbs., and contain 5-)0 lbs. of explosive. The fuse is placed either in the point or base, according to its design. The sub-caliber projectiles are smaller in diameter than the bore of the gull, and have no rear extension carrying rotating blades. The blades are attached directly to the body, near the rear end. They occupy a portion of the space between the body of the shell and the bore of the gun, at the same time serving to center the rear end of the shell in the bore. The front end is centered by four wooden blocks which drop off as soon as the shell leaves the muzzle. They are held m place by pins entering into the shell. A wooden disk or gas cheek is placed in rear of the projectile, filling the bore completely, and preventing any escape of air.
The body of the projectile is made up similarly to the full-caliber, except that the charge only fills about three-fourths of it, the remaining space at the rear being left empty. This is done to keep the center of gravity forward of the center of figure, and so maintain steadiness of flight. Sub-caliber shells 6 in. in diameter, and about 0 ft. long, weighing, filled. 1501bs., contain a charge of 5;) lbs, ; those 8 in. in diameter, 6 ft. 5 in. long, weighing, tilled, 3110 lbs_ contain a charge of 100 lbs. and those 10 in. in diameter, 7 ft. 8 in. long, weighing, filled, 50d lbs., contain a charge of 200 lbs.
Fuses of various kinds have been used the most noted being Captain Zalinski's electrical fuse. It consists of fuses, one to act instantaneously upon striking a solid target, such as the hull of a ship ; the other to act upon entering the water, either instantly or after some seconds of delay. The first may be called an impact fuse, and the second an immer sion fuse. The former consists of a battery containing liquid, ready for action, connected
through a 'low tension" primer. Upon striking the target, the circuit is elosol and the primer explode.l. This explodes the detonating charge oedry gun-cotton or dynamite, and that in turn explodes the whole charge. in case the shell misses the target and enters the water, the immersion fuse nets. This is similar to time other except that the buttery contains no exciting, liquid—is perfectly dry. As the shell enters the salt water, the battery becomes wet and active. which immediately causes explosion. unless a delay is desired, in which case a powder train is used. Mechanical fuses have been sometimes used. These generally act by impact either against a solid target or the water. An ingenious fuse of this class was designed by Mr. II. P. Merriam. One of its most peculiar features is a small wind-mill at the point of the shell, which unlocks the firing hammer as the shell passes through the air. It has two sets of caps, one intended to net when the shell strikes a solid target, the other when it strikes the water, 'The water enters an opening in the point and presses a plunger backward, driving the caps against the hammer, which in this case is a steel bail, When it solid target is struck, the point of the shell is crushed in, thus firing a set of caps arranged inside. Relay action can be given by a powder train.
The projectiles are not designed for penetration, but at Shoeburyness in England, a 10-in. sub-caliber, weighing 500 lbs., was fired into a butt of sand, situated 000 yds. from the gun, and it penetrated 47 ft. The accuracy of fire is very remarkable, even when compared with modern rifles. The following table is a record of the ranges and deviations obtained at Shoelairy»ess during experiments by the English Government.