If pressed to name the most important, or most useful, weapon in the Dahlgren family, I’d make the case for the XI-inch Shell Gun. The Navy employed that weapon in every possible guise during the Civil War (and beyond). The weapon served widely across the fleet in some of the most historic engagements. The USS Monitor carried XI-inch guns into action at Hampton Roads on March 9, 1862. Other ironclads employed XI-inch guns in the attack on Fort Sumter on April 7, 1863. XI-inch Dahlgrens of the USS Kearsarge smashed the CSS Alabama in the Battle of Cherbourg on June 19, 1864. I’d make the case the XI-inch Dahlgrens were the most “storied” of the family.
The XI-inch gun requirement rose from practical considerations of the advances in ship propulsion technology in the 1850s. In his book, Shells and Shell-guns, published in 1856, John A. Dahlgren wrote:
The earliest steamers were driven by the sidewheel, and so continued for man years later. This arrangement conflicted directly with the system of broadside armament, both as regarded the number of guns and their position.
In the first place, it was impossible to carry the customary proportion of pieces in a vessel of this description, because the steam power occupied so much of the space commonly allotted to stowing provisions and water, that the crew required for a full broadside, could not be provided for. Therefore, it was necessary to reduce the number of men, and as a consequence, the number of cannon; independently of which, the latter could not be accommodated in the broadside, because the huge wheels and their fixtures not only covered much of its extent, but they interfered with the training of those guns for which there was room.
Thus Dahlgren suggested the largest possible caliber shell guns be mounted on pivots at either end of the ship. Such worked around the issues mentioned and at the same time met the long standing American preference to carry the heaviest possible weapons into the fight. So Dahlgren added the 11-inch caliber to the shell guns of his design. He considered that caliber the heaviest which could be worked at sea.
The first production batch came from West Point Foundry in 1856. Of these early guns, at least one was expended in extreme proofing.
However, the XI-inch shell gun met with some skepticism among the Navy’s ship captains. After all, a XI-inch shell weighed some 136 pounds! To settle this, Dahlgren went to sea with one of the XI-inch guns on the training ship USS Plymouth in 1857. Successful trials convinced the Navy’s senior officers that crews could work the XI-inch guns. Mounted in pivot, the gun required a crew of 25.
The XI-inch guns also served as broadside guns, most notably on the USS New Ironsides, where the screw propulsion system removed the limitations Dahlgren noted in the pre-war discussions.
At the start of the Civil War, the Navy was just beginning to equip ships with the heavy shell gun. West Point Foundry delivered 50 by the end of 1862. Included in that lot were numbers 27 and 28 which served on the Monitor. Number 40 went to sea on the Kearsarge.
In 1862, other vendors received contracts for XI-inch shell guns. During the war, Fort Pitt Foundry cast 70; Cyrus Alger provided 89; Builder’s Foundry of Providence, Rhode Island delivered 100; the firm of Hinkley, Williams and Company of Boston, Massachusetts added 100; Seyfert, McManus and Company’s Scott Foundry produced 49; the Portland Locomotive Works in Maine cast four before shifting back to engine production; and likewise the Trenton Locomotive Company in New Jersey dabbled with naval ordnance, but only delivered three guns. Overall the Navy received 465 of the XI-inch Dahlgrens.
The XI-inch gun design conformed to Dahlgren’s “soda bottle” exterior shape. The guns were cast solid with excess metal around the chase, then bored out. As the table above indicates, the bore ran 131 inches including an 11 inch chamber. The chamber used a modified Gomer profile, being rounded at the bottom instead of flat. The only major variation among the castings was with the muzzle. Contemporary records indicate the first deliveries had a “bulb muzzle,” describing the shape of the muzzle swell. Later deliveries used a “tulip muzzle.” Yet many survivors have no muzzle swell at all or at least part of the swell shaved to clear the firing ports.
The muzzle alterations continued postwar when the Navy ordered some guns converted to rifles.
The XI-inch guns served as pivot guns, broadside guns, turret guns, and even seacoast defense guns during the Civil War. In short, every conceivable position one might use a 16,000 pound gun!