Artillery Through the Ages | Page 7

revolutionary development in mid-century. They were low-hulled, armored, steam vessels, with one or two revolving turrets. Although most cannonballs bounced from the armor, lack of speed made the "cheese box on a raft" vulnerable, and poor visibility through the turret slots was a serious handicap in battle.
[Illustration: Figure 11--U. S. NAVY 9-INCH SHELL-GUN ON MARSILLY CARRIAGE (1866).]
While 20-, 30-, and 60-pounder Parrott rifles soon made an appearance in the Federal Navy, along with Dahlgren's 12- and 20-pounder rifled howitzers, the Navy relied mainly upon its "shell-guns": the 9-, 10-, 11-, and 15-inch iron smoothbores. There were also 8-inch guns of 55 and 63 "hundredweight" (the contemporary naval nomenclature), and four sizes of 32-pounders ranging from 27 to 57 hundredweight. The heavier guns took more powder and got slightly longer ranges. Many naval guns of the period are characterized by a hole in the cascabel, through which the breeching tackle was run to check recoil. The Navy also had a 13-inch mortar, mounted aboard ship on a revolving circular platform. Landing parties were equipped with 12- or 24-pounder howitzers either on boat carriages (a flat bed something like a mortar bed) or on three-wheeled "field" carriages.
RIFLING
Rifling, by imparting a spin to the projectile as it travels along the spiral grooves in the bore, permits the use of a long projectile and ensures its flight point first, with great increase in accuracy. The longer projectile, being both heavier and more streamlined than round shot of the same caliber, also has a greater striking energy.
Though Benjamin Robins was probably the first to give sound reasons, the fact that rifling was helpful had been known a long time. A 1542 barrel at Woolwich has six fine spiral grooves in the bore. Straight grooving had been applied to small arms as early as 1480, and during the 1500's straight grooving of musket bores was extensively practiced. Probably, rifling evolved from the early observation of the feathers on an arrow--and from the practical results of cutting channels in a musket, originally to reduce fouling, then because it was found to improve accuracy of the shot. Rifled small-arm efficiency was clearly shown at Kings Mountain during the American Revolution.
In spite of earlier experiments, however, it was not until the 1840's that attempts to rifle cannon could be called successful. In 1846, Major Cavelli in Italy and Baron Wahrendorff in Germany independently produced rifled iron breech-loading cannon. The Cavelli gun had two spiral grooves into which fitted the 1/4-inch projecting lugs of a long projectile (fig. 12a). Other attempts at what might be called rifling were Lancaster's elliptical-bore gun and the later development of a spiraling hexagonal-bore by Joseph Whitworth (fig. 12b). The English Whitworth was used by Confederate artillery. It was an efficient piece, though subject to easy fouling that made it dangerous.
Then, in 1855, England's Lord Armstrong designed a rifled breechloader that included so many improvements as to be revolutionary. This gun was rifled with a large number of grooves and fired lead-coated projectiles. Much of its success, however, was due to the built-up construction: hoops were shrunk on over the tube, with the fibers of the metal running in the directions most suitable for strength. Several United States muzzle-loading rifles of built-up construction were produced about the same time as the Armstrong and included the Chambers (1849), the Treadwell (1855), and the well-known Parrott of 1861 (figs. 12e and 13).
The German Krupp rifle had an especially successful breech mechanism. It was not a built-up gun, but depended on superior crucible steel for its strength. Cast steel had been tried as a gunmetal during the sixteenth and seventeenth centuries, but metallurgical knowledge of the early days could not produce sound castings. Steel was also used in other mid-nineteenth century rifles, such as the United States Wiard gun and the British Blakely, with its swollen, cast-iron breech hoop. Fort Pulaski National Monument, near Savannah, Ga., has a fine example of a 24-pounder Blakely used by the Confederates in the 1862 defense of the fort.
[Illustration: Figure 12--DEVELOPMENT OF RIFLE PROJECTILES (1840-1900). a--Cavelli type, b--Whitworth, c--James, d--Hotchkiss, e--Parrott, f--Copper rotating band type. (Not to scale.)]
The United States began intensive experimentation with rifled cannon late in the 1850's, and a few rifled pieces were made by the South Boston Iron Foundry and also by the West Point Foundry at Cold Spring, N. Y. The first appearance of rifles in any quantity, however, was near the outset of the 1861 hostilities, when the Federal artillery was equipped with 300 wrought-iron 3-inch guns (fig. 14e). This "12-pounder," which fired a 10-pound projectile, was made by wrapping sheets of boiler iron around a mandrel. The cylinder thus formed was heated and passed through the rolls for welding, then cooled, bored, turned, and rifled. It remained in service until about 1900. Another rifle giving