A Dahlgren Gun.
Captain Rodman of the Ordnance Department, put a piston in place of Bomford’s pistol-barrel and let the piston punch into a piece of copper, and then determined the pressure on the piston by forcing the same kind of a piston into the same kind of a piece of copper by a known weight. “Although not an accurate process,” it was good enough, and with the figures obtained by it before him, Lieut. John Dahlgren, of the United States navy, designed the gun of smooth outline that by its splendid success in the hands of both forces, during the Civil War, made him famous. The greatest thickness of metal was placed around the greatest strain, and a proper thickness at every inch of length of the bore.
It was not alone, however, in putting the metal where it would prove most serviceable that Dahlgren made his gun efficient. He was a metallurgist, and was careful to improve the quality of iron used.
Meantime Captain Rodman had proposed to cast cannon hollow and cool them from the interior, instead of casting a solid log of iron and boring it out on the old plan. Although the first experiments did not show any especial improvement in the strength of a gun so cast, the method was eventually found to be the best.
With Dahlgren’s model a gun of eleven inches of diameter of bore was cast in 1852. It was fired 500 times with shells and 655 times with solid shot that weighed 170 pounds, the service charge of powder being fifteen pounds. The gun was not seriously injured or worn even by the work. That settled the status of the Dahlgren guns, and from that time on they were furnished with reasonable rapidity to the new steam warships of the navy.
Meantime rifled cannon made of cast iron reinforced over the breech by a wrought-iron jacket that was shrunk on had been introduced into the American navy. They varied from thirty-pounders up to 100-pounders, and, except for the smaller calibres, were in many cases more dangerous for their crews than for the enemy. It must be told also that a cast-iron rifle known as the Brooke, because designed by Commander John M. Brooke, of the Confederate navy, was produced in Richmond that was better than the Parrott. It was strengthened in its early service days by a series of wrought-iron bands two inches thick and six wide, that were shrunk on over the breech. Later a second series of bands was shrunk on over the first, breaking joints with them, of course, and so a very good 150-pounder was produced.
Meantime one Dahlgren smooth-bore, with a bore fifteen inches in diameter, had been successfully made, and the shells for all the Dahlgren guns were provided with fuzes that could be set to explode just about where and when the gunner wished to have them do so. But whether the damage to be done by a fifteen-inch round shot smashing its way through a ship’s side would be greater or less than that of a rifle projectile boring its way through was a question that had not been decided. It was granted that the rifle had the longer range—with a reasonable elevation a rifle would carry three miles, maybe four, and do some damage when the projectile arrived, while the effective range of the smooth-bore was, say, 1,500 or 1,600 yards, though gunners made efforts, when the time came, to run in to a range of 600 yards or less instead. But, on the whole, it was the belief among American naval officers before the Civil War that the big Dahlgren smooth-bore was the best gun afloat.
Two Blakely Guns at the Brooklyn Navy Yard.