The tests were continued on October 27th, again with a huge crowd present. Only two shots were fired, both with round shot and the gun at zero elevation. On the first shot, with a 100-pound powder charge, the ball hit and richocheted 8 times on the water. Recoil drove the gun and carriage back 6 feet, 10 inches, on the base. The second shot, with a 125-pound charge, drove the gun back 7 feet, 5 inches, but the ball, hitting rough water, skipped only 5 times.

While the Ordnance Department announced that another test would be held as soon as a hulk or ship could be found for a target, the gun was never fired again during the Civil War. The huge cannon was simply included with a battery of fifteen-inch guns as a part of the permanent defenses of New York. Another test, held in March 1867, included four shots fired with 125-, 150-, 175- and 200-pound charges, all with the gun at an elevation of 25 degrees. The maximum range attained was 8,000 yards, or a little under 5 miles.

A second and slightly lighter 20-inch gun also may have been cast for the Navy in February 1864, and another was later cast in 1866. For obvious reasons, however, the guns were never much more than experimental pieces.

Rodman's heaviest cannons were fantastic weapons for their time, but from a practical point of view their usefulness was extremely limited.

Aiming time depended on the extent of adjustment, but it took an additional 2 minutes and 20 seconds to traverse the gun and barbette carriage 90 degrees. The 20-inch gun certainly would have required twice the loading and aiming time of the 15-incher.

Hitting a fast-moving ship at any reasonable range with the one shot that could be gotten off in time would have depended largely on luck.

Rodman's guns proved his theories, but the 20-inch gun was still too big to be a really effective weapon. These large guns still exist. Old "No. 1" still sits at Fort Hamilton in Brooklyn, New York, now a public park located near the Verranzano Narrows Bridge. The second 20 inch Rodman looks out over New York Harbor from Fort Hancock at Sandy Hook, in New Jersey.