Rodman Cannon
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Fort Schuyler was one of the many forts that were built along the east coast in the aftermath of the War of 1812. The United States government realized that there were little to no land based defenses that would be able to protect the many harbors that dotted the coastline. Fort Schuyler is located on the easternmost point of Throggs Neck, on a narrow spit of land which extends into the Long Island Sound at its junction with the East River. The actual construction of the fort began in 1833, after the land had been sold to the federal government in November of 1826. The mission of the fort was to protect New York City from attack by sea by closing off the western end of Long Island Sound. The fort was built using granite brought from Greenwich, Connecticut. Masons came from all over New England to work on erecting the forts massive walls. A sizable Irish community sprang up in what soon became known as Schuylerville. By the year 1845 the fort was finally ready for armament. 312 seacoast and garrison guns, six, field pieces and 134 heavy guns were mounted in their respected places. In 1856 the installation of the guns was complete. When the fort was completed, it was said to have been the finest example of the French type of fortification for the purpose of both sea and land defense in the United States.
There were three tiers of guns. Two tiers in casemates and one en barbette. This meant that the two lower tiers were located in a vaulted, shellproof chamber inside the fort and were fired through openings in the walls. The uppermost guns were on a platform above and were located high enough to permit firing over the walls. Should an enemy battleship pass a certain point it would be exposed to the fire of at least three heavy guns and a slew of covering fire. Howitzer emplacements were also installed and in a combat situation would be used to fire over the walls upon an approaching enemy. The walls of the fort are protected by three full bastions at the salients on the water side and two smaller bastions on the land side. The purpose of the bastions is both to protect the walls and also to give a wider firing range to the forts guns.
In 1844, a young ordnance officer named Lieutenant Thomas Jefferson Rodman began a long series of experiments that were aimed at overcoming the difficulties of casting large iron cannons. This difficulty set a maximum size limit to cast iron artillery pieces. In this time period, cannons were cast around solid cores, and could only be cooled from the outside. Doing so caused the cooling metal to contract towards the outer surface of the cannon barrel and created internal strains and structural irregularities in the metal. Large guns often had a habit of cracking when they were cooled, breaking in transport, or bursting when they were fired.
Thomas Rodman devised a theory that would account for both the internal strains and imperfections and for variations in the density, hardness, and tensile strength of the metal in cast iron cannons. He came up with a plan to cast cannons around hollow cores, which would then be cooled from the inside, rather than externally, by simply using a stream of running water. Rodman believed this would cause the cooling metal to contract towards the bore and increase the density of the metal where it was most needed. The bore would later be reamed out and polished, eliminating any imperfections on the surface. The rate of cooling could be controlled by regulating the temperature and rate of flow of the water.
Using this method, Rodman claimed he could cast cannons of any size. While working at the Fort Pitt foundry in Pittsburg, Pennsylvania, Rodman began a series of experiments in trails which lasted nearly ten years. His experimental cannons were cast in pairs, one with the old solid core and the other around variations of his own hollow core. Out of one of the pairs, the gun that was cast using Rodmans theory was fired nearly 1500 times. Its twin, cast using the solid core method and cooled externally, burst on the 299th shot. During another test of guns purposely made of the poorer material, Rodmans internally cooled gun fired 250 times and helf together just fine. The other cannon burst firing the 19th round. The War Department was completely satisfied with Rodmans results, and in 1860 authorized the casting of a 15 inch smoothbore columbiad using Rodmans casting method. It was a gun larger than anything the world had seen before. It weighed 49,000 pounds, was just under 16 feet long, and fired a 450 pound solid shot. This cannon was eventually sent to Fort Monroe, Virginia, where it was tested in March of 1861 and became a model for the many Rodman guns that followed.
Rodmans newest monster–one of the largest iron castings to say nothing of the largest gun ever attempted–was three years in the making. Expected to weigh over 100,000 pounds finished, the gun was much heavier than the 40-ton capacity of Knapp, Rudds largest furnace. The foundry, however, had a total pouring capacity of 185 tons, and expected to cast the new gun from six furnaces at once. New plans had to be drawn, molds had to be made, new casting procedures were essential, and new finishing machinery had to be designed and built.
The great day finally came on February 11, 1864. With Major Rodman, then superintendent of Watertown Arsenal, Mass., supervising the operation, the huge gun was poured. Filled in sequence from different furnaces, the 4-piece mold took 160,000 pounds of molten iron. Cooling, by both running water and streams of air, took nearly a week, after which the gun was finished on a specially built lathe. The finished barrel weighed 116,497 pounds, and the muzzle of the gun was inscribed: “20 inch, No. 1, Fort Pitt, 116,497 lbs.”
Destined for Fort Hamilton in New York harbor, the gun was placed on a double railway truck, also specially built, at the foundry to await shipment. As the Pittsburgh Gazettte reported on July 23, 1864, “Juveniles, aged from ten to fifteen years, were amusing themselves today in crawling into the bore on their hands and knees. A good sized family including ma and pa, could find shelter in the gun and it would be a capital place to hide in case of a bombardment.
Rodman supervised the building of a special carriage for the 20-inch gun at Watertown Arsenal, for the cannon was far too big for any standard mount. The finished product, an iron frontpintle barbette carriage weighing 36,000 pounds was shipped off to New York and assembled at Fort Hamilton.
The 20-inch gun was a sizable piece of artillery. Total length was 20 feet, 3 inches, with the bore length 17 feet, 6 inches; thus the bore length-diameter ratio of 10.5 was even lower than that for the 15-inch Rodman gun. Both the shot and the shell for the 20-incher were more than twice