English: Thomas Jackson Rodman graduated from the military academy in 1841 and was assigned to the Ordnance Department at Allegheny Arsenal in Pittsburgh. He invented a manufacturing method known as the "wet chill process". He arranged for the Fort Pitt foundry to cast and test his cannons. In 1849, it was found that cannons produced by his method were superior to all other guns produced in this country. A prototype 15-inch cannon was cast on December 23, 1859. During the gun trials 509 proofing rounds were fired without mishap. The first government purchase order for these 50,000 pound, 190 inch long weapons was issued in November 1861. During the Civil War the Rodman's guns were the largest in the U.S. arsenal. Two 20-inch guns and the 15-inch gun, along with the 200 pounder (12-inch) muzzle loading Parrott Rifle, became Union's main seacoast armament. A 15-inch Rodman at Fort Monroe kept the C.S.S. Virginia (Merrimac) at bay during her struggle with the Union's U.S.S. ( NPS )