Earlier I mentioned some connections between the biggest of the Dahlgren guns and the Army’s Rodman guns. These weapons were contemporaries, as of course were the inventors – John A.B. Dahlgren and Thomas J. Rodman. But while the Army’s Rodman guns were designed almost exclusively for seacoast defense, Dahlgren’s designs covered practically all the Navy’s requirements. Given the varied nature of such requirements, the term “Dahlgren” might refer to several different types.
We can generally group the Dahlgrens within three “families” – the boat howitzers, the heavy smoothbores, and the heavy rifled guns. I’ve discussed the boat howitzers in detail (but should return to complete the discussion of the various subtypes at some point). The rifled Dahlgrens, I must likewise table for the moment as they don’t factor yet sesquicentennial-wise. I’ve already discussed the IX-inch and XV-inch Dahlgren guns. So it is time I introduce the family of heavy smoothbores:
I’ve organized this diagram to show the three generations of Dahlgren’s heavy smoothbore guns: pre-war, wartime, and post-war. The vertical columns show the various calibers of these heavy smoothbores. Again, notice the use of roman numerals with the weapon designations, which was the Navy’s practice at the time.
Within those generations are four sub-types: the original shellguns (blue-gray), wartime solid-shot guns (tan), the turret guns for the ironclads (gray), and the postwar derivatives (gold).
First, the original shell guns. When discussing the IX-inch shell guns used by Confederates at Charleston in 1861 (and which were still there in 1863), I offered this table comparing the particulars of the Dahlgren Shellguns:
These were the four main calibers of shellguns entering service in the years just before the Civil War. As the family diagram shows, there was a 32-pdr shellgun. But this was apparently just a developmental weapon, with few produced. The VIII-inch guns went through a design change during the war, resulting in a heavier version. Production run of that heavier VIII-inch shellgun was 351, from 1864 to 1867.
As their name implies, the shellguns featured a design optimized for firing shells. There’s a long story behind the employment of shells for naval ordnance. The short version – by the first half of the 19th century fuse, projectile, and cannon design reached a point that the shell was a viable option for naval use. While traditional solid shot, depending on raw kinetic energy, could damage wooden ships, the shell’s explosive power offered certain advantages. Dahlgren designed these shellguns to fire primarily shells, with the option to use solid shot when needed.
The shellguns served the Navy well, particularly the IX- and XI-inch guns. These included perhaps the most historic of all the guns used in the Civil War, the XI-inch guns in the turret of the USS Monitor.
And of course there were a few other famous Dahlgren shellguns, also of XI-inch caliber.
But we’ll get to the guns of the USS Keokuk in due time.
By mid-war, the Navy realized a requirement for guns which could fire solid-shot, along with the occasional shell (in other words, the opposite of the original shellguns). Consequently, the Navy’s Bureau of Ordnance designed a set of guns based on Dahlgren’s original design. The requirement for these guns was to fire solid shot against armored warships, with high durability in mind. Such accounts for the heavier weight.
At any rate, the solid-shot guns came in four calibers:
- 32-pdr of 4,500 pounds. 379 produced between 1864-67.
- VIII-inch of 10,000 pounds. Only one produced in 1864.
- IX-inch of 12,280 pounds. Only one produced in 1865.
- X-inch of 16,500 pounds. 29 produced in 1862-65.
The production figures offer an indication these guns were not entirely successful. The aberration being the large number of 32-pdrs produced. The need for weapons on smaller craft (river and inshore patrol) might account for a healthy production run. But what has been lost to time is why such production continued well after the war.
While the solid-shot guns were not deemed successful enough as anti-ironclad weapons, the big turret guns were. As mentioned in the post about the XV-inch guns, Dahlgren had some reservations about casting guns larger than XI-inch. So many of the XIII-, XV-, and XX-inch used the Rodman casting technique as a “hedge.” These joined the XI-inch shellguns in the early monitors. By war’s end, the preference was for uniform caliber armament in the turrets. The Navy received only eleven of the XIII-inch guns. The lone XX-inch gun produced during the war was not delivered to the Navy, but later sold to Peru. But as mentioned earlier, the XV-inch guns became the Navy’s standard turret guns (going through a few design revisions along the way).
And to close out the “family tree” of the heavy Dahlgren smoothbores, these weapons saw long post-war service. With the heaviest of the family holding an important position as the primary armament of the Navy’s vaunted ironclads, some XV- and XX-inch guns appeared with slight improvements. The last twenty XV-inch guns featured Army-style elongated hemisphere bore bottoms. Three additional XX-inch guns conformed to a revised, slightly smaller, design in 1866-7. But none of those saw active service.
The long line of Dahlgren smoothbores ended, much as with the Army’s Rodmans, with a conversion.
Just over fifty XI-inch shellguns underwent an involved process with the aim to extend their usefulness a few more years. The modifications were done between 1876 and 1880. In addition to a rifled sleeve inserted into the bore, the guns also had their trunnions modified to retain the preponderance.
These heavy Dahlgrens served the Navy from the mid-1850s up to the eve of the 20th century. Although woefully inadequate at the time, a few of these old Dahlgrens were on the equally inadequate old monitors pressed into brief service during the Spanish-American War. After that time, just like the Army’s old Rodman guns, the Dahlgrens mostly went to scrap. But in a few cases, guns were salved for use as gate guards, bollards, or memorials. A fitting end for such long-serving guns.