I’ve detailed the design and production histories of the 8-inch, 10-inch, 12-inch Rifle, and 15-inch Rodman Guns. Before I turn to the “big brother” of the set, the 20-inch Rodman, for sake of complete coverage I should mention the 13-inch Rodman smoothbore gun.
Thomas J. Rodman’s 1861 patterns included the 13-inch gun with proportions between that of the 10-inch and 15-inch guns:
Fort Pitt Foundry cast one 13-inch Rodman in mid-1863, the only gun of that caliber cast to Rodman’s original pattern. Given the time frame, the gun likely had no preponderance and sockets for the updated elevating system.
Two more 13-inch guns appear in the records, but differ from the original pattern. In 1866, Cyrus Alger delivered a pair of 13-inch Rodmans. The first used the mold of a 15-inch Rodman, but bored to the smaller caliber, weighing over 51,000 pounds. The exact pattern for Alger’s second is unknown, but it weighed 38,500 pounds. The heavier of the pair went to the test range for trials and burst after firing over 700 rounds. Testimony attributed the failure to tests of quick burning powder, which generated many times the pressure of the mammoth powder used in service.
Very likely the third 13-inch Rodman became the subject of a different experiment. An 1878 report to Congress details the conversion of a 13-inch Rodman smoothbore to a 10-inch rifle. Starting with a 13-inch gun cast in 1866, South Boston Foundry, which Alger’s facility became in the 1870s, reamed out the bore to 17 inches. The foundry then installed a wrought iron rifled bore and jacket. The rifling pattern included seventeen grooves each just under one inch.
The product weighed 40,320 pounds. The weight is within the range expected if the second of Alger’s guns was the subject of conversion. But the report does not offer a foundry or registry number for conformation. Regardless the gun went to Sandy Hook, New York for tests. Like many expedients of the late 19th century, the conversion offered little gain for the money expended.
While not produced in numbers, the 13-inch Rodman appeared in post-war plans. In 1867 a board of engineer, artillery, and ordnance officers recommended the 13-, 15-, and 20-inch as the preferred smoothbore calibers. The recommendation apparently carried weight, for as late as 1891 the Manual for Heavy Artillery listed 13-inch smoothbores as “in the system.” Although General John C. Tidball noted it should be considered an “experimental type” as only a few were produced. In some regards this reflected American strategic thought at the time. Should war come again, the Army and Navy would have ample time to re-arm with the preferred weapons.
I would question why the 13-inch gun ever existed to begin with. Certainly the 15-inch gun provided greater firepower. In the context of coast defense, what part entrances could the 13-inch cover that the 10-inch could not? Particularly with the coastal forts of the time positioned with the older seacoast guns in mind. Then again I was not an ordnance officer in the 1860s!
None of the 13-inch guns survive today, leaving us with a few line drawings and congressional testimonies to tell their story. And that story is but a footnote in the larger chapter of the Rodman guns. The 13-inch guns were the unsuccessful sibling of the family.