The biggest gun of all — the 20-inch monster for which no target would serve
A photograph of the only 20-inch gun made during the war. It weighed 117,000 pounds. On March 30, 1861, a 15-inch Columbiad was heralded in Harper's Weekly as the biggest gun in the world, but three years later this was exceeded.
In 1844 Lieutenant (later Brigadier-General) Thomas Jefferson Rodman of the Ordnance Department commenced a series of tests to find a way to obviate the injurious strains set up in the metal, by cooling a large casting from the exterior.
He finally developed his theory of casting a gun with the core hollow and then cooling it by a stream of water or cold air through it. So successful was this method that the War Department, in 1860, authorized a 15-inch smoothbore gun. It proved a great success.
General Rodman then projected his 20-inch smooth-bore gun, which was made in 1864 under his direction at Fort Pitt, Pittsburg, Pennsylvania.
It was mounted at Fort Hamilton, New York Harbor, very soon afterwards, but on account of the tremendous size and destructive effect of its projectiles it was fired only four times during the war. It was almost impossible to get a target that would withstand the shots and leave anything to show what had happened.
These four shots were fired with 50, 75, 100 and 125 pounds of powder.
The projectile weighed 1,080 pounds, and the maximum pressure on the bore was 25,000 pounds. In March, 1867, it was again fired four times with 125, 150, 175 and 200 pounds of powder, each time with an elevation of twenty-five degrees, the projectile attaining a maximum range of 8,001 yards. This is no mean record even compared with twentieth century pieces.
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