Such guns are built up of a tube or “core” of steel of the required size, upon which is shrunk a jacket, covering the rear, or breech half of the core, outside of which are shrunk on several broad hoops. The cutting out of the bore to exactly the proper caliber and the plowing of the spiral riflings put the gun in readiness for its breech-closing and other attachments. This process requires several months, involves large capital and powerful machinery, and good results imply the very highest workmanship. [Illustration: THE UNITED STATES CRUISER “BROOKLYN” (STERN VIEW).] Such are the guns of modern men-of-war; and a first-class battle-ship carries four twelve- or thirteen-inch rifles (that is, having a bore twelve or thirteen inches in diameter), several eight- or ten-inch rifles, and many smaller guns arranged to be fired with extraordinary speed, and hence called “rapid-fire” guns; while her upper works and “military tops” fairly bristle with fierce little six-, four-, and one-pounders,—revolving magazine rifles, capable of discharging rifle-balls as fast as a man can turn the crank. [Illustration: ON BOARD A BATTLE-SHIP GOING INTO ACTION. WORKING THE RAPID-FIRE GUNS.] To give some idea of the size and power of one of the 13-inch guns, whose long muzzles, in pairs, project so far out of the turrets that hide their mountings and firing-crew, let me tell you that it is 40 feet long, more than 4 feet in diameter, and weighs 60½ tons. “It requires 550 pounds of powder to load it, and the projectile weighs half a ton. The muzzle-velocity of the projectile is 2100 feet per second, with the stated charge, and its energy is sufficient to send it through 26 inches of steel at a distance of 600 yards. At an elevation of 40 degrees the range of the gun will be not far from 15 miles.”