A built-up gun is made of several layers of forged steel. The parts of such a gun are known as the liner, the tube, the jacket and the hoops. The liner is a single piece which extends the length of the bore and is intended to contain the rifling and the powder chamber. This is inclosed by the tube, which is also in one piece, surrounding the liner throughout its length. Outside this is the jacket, made in two pieces and shrunk on the tube. Over the jacket lie the hoops, six or seven of these being used in a big gun. Like the jacket, these also are shrunk on. All these parts are made of the finest quality of open-hearth steel.

These pieces are prepared with the utmost care to prevent any defective material entering into the make-up of the gun. After the parts are put together a thorough

Five-Inch Naval Gun and Mount The latest type of gun used in the U. S. Naval Service in the secondary batteries on a battleship..

Coast Defense Gun.

A modern 14-inch coast defense gun at Sandy Hook. The gun is mounted on a disappearing carriage, which lowers it out of sight behind the breastworks after firing. This is one of the most powerful guns in the world, firing a projectile which would pierce the armor of a battleship more than five miles away.

Copyright by Underwood & Underwood, N. Y. A BATTERY OP 12-INCH COAST DEFENSE MORTARS.

These powerful weapons fire a projectile which weighs from 700 to 1,046 pounds, depending on the range desired, and which is capable of piercing the deck armor of any battleship. They have a range of 20,000 yards with the 700-pound projectile. The gun is 16 2/3 feet long and is fired only at elevations between 45° and 65°.

Giant Guns - Their Muzzle-Energy, Projectiles, and Penetrating Powers.

The British 13.5, which was known as the 12-inch-A until the "Lion" was launched, has a length of 45 calibers, and a muzzle-energy ten per cent greater than that of the 50-caliber 12-inch of 1909 and 1910. It may be noted that the caliber is the diameter of the bore of a gun. The statement that a gun has a length of 45 calibers, for example, implies that the gun is forty-five times the bore's diameter. Thus a 12-inch gun of 45 calibers is 45 feet long.

forging follows, either by use of hammer or press, the latter being now used in preference. The usual practice in forging is to continue it until the ingot is decreased to one-half its original thickness and is within two inches of the desired diameter of the finished work. It is then annealed with great care to relieve the strains set up in the metal by the forging and next goes to the machine shop to be rough bored and turned. The final boring takes place after a second annealing. The above is only a rapid sketch of the total process, in which elaborate care is taken to prevent imperfection of any kind.

Ordnance Proving Ground.

View showing smoke cone occurring during the proof firing of a twelve-inch gun with brown powder.

Courtesy of the Bethlehem Steel Co.

In a wire-wound gun an inner tube of steel is thoroughly wrapped by successive layers of ribbon wire, each layer being wound with wire at a different tension. This type of gun is preferred by foreign manufacturers, but within the United States the built-up system is in higher favor and is almost exclusively employed. The makers of the wire-wound cannon claim for it a positive soundness of material impossible to secure in a built-up gun, and that it has greater firmness of material and superior tangential strength. But with this come certain disadvantages, a notable one being a lack of rigidity in the longitudinal direction, this tending to increase the "droop"of the muzzle and give a certain "whip" to the piece when fired that reduces accuracy. This and other disadvantages have given the built-up guns general preference in this country, they being found strong enough to bear any pressure desirable in service. In addition they are much cheaper to build then the wire-wound guns.

Modern heavy guns are made of medium open-hearth carbon steel, forged as stated. The liner and tube are then placed upright in an assembling pit, the jacket and hoops shrunk on, and the finishing work done, as above said, the breech mechanism being finally fitted. Within recent years there has been a steady increase in the size and range of cannon, until an immense size and weight have been attained. For naval purposes the 14-inch gun is the largest now used in American battleships, but in the United States coast defense forts, 16-inch guns are installed. England lias equipped several of her latest battleships with 15-inch guns and other nations are following in the same direction. In recent great battleships four turrets are used, each carrying three of these great guns, giving a broadside of twelve of these monster weapons of war. Of the three guns, the middle one is raised above the line of the others. A battleship thus armed is able to fire six guns ahead and six astern by raising the second and third turrets so as to fire over the others.

Four-inch Fifty Caliber Rapid-Fire Gun on Pedestal Mount.

Extraction of cartridge case by opening of breech mechanism. Weight of gun, 6,170 pounds. Length of gun, 205 inches (51.2 calibers). Weight of projectile, 33 pounds. Travel of projectile in bore, 165.6 inches (41.4 calibers). Weight of charge, 15 pounds of smokeless powder. Muzzle velocity, 2,900-foot seconds. Muzzle energy, 1,928-foot tons. Weight of mount with shield, 9,470 pounds. Thickness of shield, 2 inches of nickel steel. Gun equipped with telescopic and night sights and with electric and percussion pull-off firing gear.