Statistics for occurrence #1 of “Fort Pitt” in chapter 8 of The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 5: Forts and Artillery.:

...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 f...
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