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 smooth-bore 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.