John Dalhgren’s Heavy Smoothbores for the US Navy
Rear Admiral John A. Dahlgren aboard USS Pawnee pictured with a 50-Pounder Dahlgren Rifle. US Naval History and Heritage Command Photo
After being assigned the the Washington Navy Yard in 1847, Lieutenant John Adolphus Bernard Dahlgren would design a series of heavy smoothbore cannon which would equip the United States Navy during the Civil War era and beyond. Dahlgren was also the inventor of new firing locks for US Navy cannon, light boat howitzers, and a type of rifled cannon. In 1863 he left his work at the US Navy Bureau of Ordnance to take command as a Rear Admiral of the ironclad ships of the US Navy’s South Atlantic Blockading Squadron.
The aim of this essay is provide a general overview of John A. Dahlgren’s heavy smoothbores designed for the US Navy. His other work - especially his designs for boat howitzers and rifled cannon - will be covered in the future.
US Model 1845 32-Pounder of 57 Hundredweight. Cannon is on display on the Hudson Town Common in Hudson, New Hampshire. Photo from Wikimedia by user “Daderot” who dedicated this photo to the Public Domain.
When Lieutenant Dahlgren arrived at the Washington Navy Yard, the US Navy had just adopted a new system of uniform armament. Nearly all cannon aboard US Navy vessels would be 32-pounders. All the guns would fire the same 32-pound round projectiles. What would vary would be the amount of gunpowder used to propel those projectiles. The lower decks of ships of the line and heavy frigates would carry the heaviest 32-pounders like the 57 hundredweight gun above. Upper decks would carry much lighter 32-pounder guns. These lighter guns would fire the same projectiles but with much smaller powder charges.
The system was far from perfect. The heaviest, most powerful guns lacked accuracy. The lighter guns were more accurate but lacked power. An incident on November 13th, 1849 also showed that the guns were not safe. One of the new heavy 32-pounders burst while Dahlgren was test firing it. A warrant officer standing next to Dahlgren was killed and a huge piece of the gun landed a foot from Dahlgren. This event inspired him to design a better system for US Navy ordnance. (Dahlgren, John. Autobiograpy. Chapter 2 “Ordnance Development to the Civil War, 1847-1860).
1864 View of the IX-inch Dahlgren Smoothbores aboard USS Hartford. US Naval History and Heritage Command Photo: https://www.history.navy.mil/content/history/nhhc/our-collections/photography/numerical-list-of-images/nhhc-series/nh-series/NH-53000/NH-53678.html
Dahlgren was very critical of the 1845 system of uniform 32-pounder caliber. In his autobiography he states “The object (of the new system) was to have but one calibre of gun and therefore one size of shot in all the ships, thereby avoiding the mistakes apt to occur in action, where so many pieces were to be supplied and so rapidly. This was a good object but the Board make a mistake in carrying it out - by adapting the 32 pounder as the unit calibre - because we had then the 42-pounder in service which was better because it was more powerful. By taking the 32-pounder as the unit, they sacrificed the best guns in the service. They should have taken the 42-pounder or even higher as the unit calibre. But they unluckily persuaded by the example of the English Navy which had just adopted the 32-pounder unit-calibre - they not only did this but they copied the weights and models of the guns, so that our system became an imitation of the English - so we actually retrograded - It was this system that I finally overthrew after a struggle of seven or eight years, and for the 32-pounder and 8” shell guns gave the Navy my IX-Inch and XI-inch guns - firing shells of 72lbs and 130lbs - and shot of 96lbs and 170lbs - it was the XI-inch guns of the Kearsarge that beat the best English Guns on the Alabama and vindicated my theory.” (Dahlgren, John. Autobiograpy. Chapter 2 “Ordnance Development to the Civil War, 1847-1860).
IX-inch Dahlgren from USS Southfield (and later CSS Peedee) displayed at the Florence Veterans Center, Florence, SC. (Author’s Photo)
Dahlgren believed that the future of naval artillery lay in shell guns - a theory originally developed and promoted by French artillery officer Henri-Joseph Paixhans in the 1820s. By the 1840s, both the US Army and US Navy had adopted 8-inch and even 10-inch shell firing guns. However, these guns were too lightly built to be able to fire solid shot. (An explosive shell, because it has a hollow center for its charge, weighs significantly less than a solid shot of the same caliber.)
Dahlgren designed guns that were strong enough to fire both shot and shell. Dahlgren’s 9-inch gun weighed around 9,000 pounds - nearly half again as much as the heaviest 32-pounders. But they could fire shot weighing nearly three times as much. They could fire an exploding shell even more devastating than the 8-inch shell guns in service. And they were far more reliable and safe for the users than the cannon that preceded them.
Matthew Brady photo of a US Navy 9-inch Dahlgren on a pivot mount with its crew (possibly aboard USS Miami). The “soda bottle” shape of the gun is easily visible in this photograph. US Naval History and Heritage Command Photo: https://www.history.navy.mil/content/history/nhhc/our-collections/photography/numerical-list-of-images/nhhc-series/nh-series/NH-61000/NH-61933.html
This late 18th century 24-pounder cast in Maryland (and displayed in Georgetown, SC) shows features typical of naval guns of an earlier era. Note the very gradual narrowing from the breech to the muzzle. Note the bands called “reinforces” which are part of the cast and which were thought to help strengthen the gun. Note the pronounced muzzle swell thought to strengthen that area of the gun. (Author’s photo)
Unlike traditional naval cannon which were thickest at the breech but thinned only very gradually toward the muzzle, Dahlgren designed cannon that were far thicker at the breech before thinning considerably. Gone were the the “reinforcing” rings cast into the cannon along the way. The shape was derided by some as resembling a “soda bottle”, but Dahlgren had designed the guns in light of research (some of it his) that showed that the pressure of the exploding propellant charge was greatest right at the breech before dropping considerably as the projectile moved towards the muzzle. A thick breech with a relatively thin remainder of the barrel resulted in a gun that was both stronger and lighter than earlier designs for a given caliber.
USS Kearsarge’s after XI-inch pivot gun after that ship sank CSS Alabama. Note that most of Dahlgren’s guns retain a slight muzzle swell - a nod to traditional looks in an otherwise untraditional gun. US Naval History and Heritage Command Photo: https://www.history.navy.mil/content/history/nhhc/our-collections/photography/wars-and-events/the-american-civil-war--1861-1865/the-battle-of-cherbourg/nh-1261.html
Dahlgren intended his 9-inch guns to be broadside weapons mounted on an adapted version of the traditional naval gun carriage. (The Marsilly carriage had two wheels at the front but skids at the back to increase the friction upon the deck as the gun recoiled.) The 9-inch guns would be mounted on gun decks of ships in the traditional style. However, he designed an 11-inch gun as a heavy pivot gun to be mounted in small numbers on the upper decks of ships. Rather than having one gun for each side, a single heavy 11-inch gun would be able to be pivoted to fire from either side of the ship. By the standards of the mid-19th century, the 11-inch gun was huge, weighing nearly 16,000 pounds. There was opposition within the navy to mounting such an enormous gun aboard ship.
11-inch Dahlgren recovered from USS Keokuk on display at White Point Garden in Charleston. (Author’s photo)
Dahlgren’s 9-inch guns were adopted as the main gun-deck armament of the huge Merrimac-class steam frigates of 1854. However, his proposal to mount the 11-inch guns on their upper “spar” decks were rejected. Instead, he was asked to design a 10-inch gun according to his principles - one of which would be mounted at both the bow and the stern on pivot mounts - while the majority of the spar deck would be armed with the older model 8-inch shell guns in broadside carriages. There is no known surviving 10-Inch Dahlgren smoothbore. USS Cumberland’s 10-Inch Dahlgren was recovered after the Civil War. It was displayed in Michigan (photo below), but it seems to have been scrapped during the World Wars.
Photo displayed at the Hampton Roads Naval Museum. Image is believed to be the 10-Inch Dahlgren Smoothbore recovered from the wreck of USS Cumberland. This cannon, like nearly half of Civil War era cannon which had been preserved, was scrapped during the World Wars.
9-inch Dahlgren on the gunboat USS Hunchback (a converted ferry). Note the two-wheel Marsilly carriage and the lock (firing hammer) visible on the breach of the gun. Library of Congress Photo: https://www.loc.gov/pictures/resource/ppmsca.80234/
Dahlgren pressed for a command at sea to be able to prove that his XI-inch guns were manageable and could be effective. Dahlgren wrote, “After much solicitation - by me and by opposition from men who should not have done so, I obtained command of the Plymouth, a fine Sloop of War with full leave to alter and arrange at my pleasure - one of the redoubtable XI-inch guns that a frigate was not supposed to be able to carry was mounted on the Plymouth and I proceeded to sea.” His trials with the 11-inch gun aboard USS Plymouth (a sloop-of-war was smaller than a frigate) demonstrated that the huge gun could be worked.
9-Inch Gun which served on USS Minnesota preserved in New Hope, Pennsylvania. Note the post-war iron two-wheel Marsilly carriage. Photo by Wikimedia user “Pbritti” and declared Public Domain.
Dahlgren took great pride in his IX-inch and XI-inch guns. In his autobiography, he seems to relish reporting every occasion on which his 9 and 11 inch guns gave good service. And he had good reason to be proud. These two designs were very successful, powerful guns which gave good service to the United States Navy during the enormous trial of the Civil War. The US Navy used these guns on nearly all of their purpose built ships and almost all of their acquired ships that were large and strong enough to mount them. While they may not have had the accuracy or range of Parrott’s rifles, they were far more reliable. No 9-inch or 11-inch gun is reported to have burst in service during the war. While rifles may have been more accurate on land, at sea in an era before gyro-stabilization and electromechanical or hydraulic movement, any gun fired over open sites would have only limited accuracy on a rolling ship. Smoothbores also offered the advantage of being able to “skip” their round shot and shell over the water much like a stone can be “skipped” by throwing it over smooth water.
Dahlgren also found (a bit by trial and error) that his guns were strongest when cast of relatively uniform thickness from breech to muzzle. The “soda bottle” shape was then created by turning the cylindrical gun block on a lathe to remove the excess thickness on the muzzle end. (Olmstead et al. provide wonderful drawings of the “cut away” portions of the casting in their book The Big Guns.) Dahlgren’s guns were cast solid in the traditional manner. The barrel was then bored out of the solid gun block.
US Army 8-inch “Rodman” Columbiad preserved in Newton, NC. Rodman’s guns are similar in shape to Dahlgren’s. Rodman’s guns were cast using his “hollow method”. Only 15-inch and late-war 11-inch Dahlgrens were cast using Rodman’s methods. (Author’s Photo)
US Army Captain Thomas Rodman developed in the late 1850s a method of hollow casting heavy guns which ran hot water into what would become the barrel of the still molten gun being cast. This cooled the gun from the inside out, resulting in the cooling metal contracting inward upon itself. Dahlgren did not think this process was needed, and he accused Rodman of basing the shape of his US Army guns upon Dahlgren’s navy guns.
While the 9-inch and 11-inch guns were some of the largest afloat in the years leading up to the Civil War. Two of the three original US Navy Ironclads would carry 11-inch Dahlgrens: USS Monitor carried two and USS New Ironsides, a broadside ironclad, carried fourteen of the 11-inch Guns. As heavy as these guns were, the rapid technological changes driven by the war would see the demand for larger and more powerful naval artillery.
Retouched image of the Ironclad USS New Ironsides. This ship carried a main battery of fourteen 11-inch Dahlgren guns and 2 150-pounder Parrott rifles. US Naval History and Heritage Command Photo: https://www.history.navy.mil/content/history/nhhc/our-collections/photography/numerical-list-of-images/nhhc-series/nh-series/NH-95000/NH-95018.html
USS Monitor in 1862 after the Battle of Hampton Roads. Note the muzzle of one of Monitor’s 11-inch Dahlgrens protruding from the turret. US Naval History and Heritage Command Photo: https://www.history.navy.mil/our-collections/photography/numerical-list-of-images/nhhc-series/nh-series/nh-1---nh-3067/nh-500---nh-599/nh-577-uss-monitor--1862-.html
The Battle of Hampton Roads in March of 1862 concluded with neither USS Monitor with her two 11-inch Dahlgrens nor CSS Virginia with her six 9-inch Dahlgrens and four Brooke rifles able to inflict significant damage upon the other. (The myth that Monitor was firing her guns with “half-charges” is incorrect. Monitor’s guns were fired with what were full charges at the time. In the aftermath of the battle, experiments conducted showed that 11-inch Dahlgrens were able to fire 20-pound, 25-pound, and even 30-pound charges of black powder propellant. Drachinfel has made a video offering a solid explanation of why this is so. Video here: https://www.youtube.com/watch?v=Od5oQjErv7k ).
Turret of USS Catskill. The muzzles of the turret’s two heavy guns are visible. To the left, the 15-inch Dahlgren is fully inside the turret - the muzzle being too large for the gun to be run out of the gunport. The gun to right is the 11-inch Dahlgren. Also on deck are two of Dahlgren’s boat howitzers. US Naval History and Heritage Command Photo: https://www.history.navy.mil/content/history/nhhc/our-collections/photography/numerical-list-of-images/nhhc-series/nh-series/NH-61000/NH-61925.html
The challenge of iron armor demanded greater power from guns. Dahlgren sought to develop a 13-inch gun, scaling up his designs and methods. However, Navy officials were impressed with the US Army’s prototype 15-inch Rodman gun in action at Fort Monroe in Virginia, and Dahlgren was ordered to develop a 15-inch. While Dahlgren had previously rejected Rodman’s hollow-casting technique, he accepted that since the only successful 15-inch gun had been cast by Rodman, the urgency of war required that his naval variant be cast using the same technique.
15-inch Dahlgren Guns - Photo Digitized by the New York Public Library: https://digitalcollections.nypl.org/items/510d47e0-80e9-a3d9-e040-e00a18064a99
Interior of the Passiac-class Monitor Montauk. This shows the arrangement of the two Dahlgren guns in this class. At left is an 11-inch Dahlgren. At right is a 15-inch Dahlgren. The gun ports on the Passiac class had not been designed with the huge 15-inch in mind. The gun was actually fired from completely inside the turret. A “smoke box” was built inside the turret into which the muzzle was run to fire the gun. US Naval History and Heritage Command Photo: https://www.history.navy.mil/content/history/nhhc/our-collections/photography/numerical-list-of-images/nhhc-series/nh-series/NH-58000/NH-58705.html
The 11 and 15-inch Dahlgren-armed monitors USS Weehawken, USS Montauk, and USS Passaic pictured as they engaged the Confederate batteries at Fort Moultrie near Charleston, SC. (Photo taken from Fort Moultrie.) US Naval History and Heritage Command Photo: https://www.history.navy.mil/content/history/nhhc/our-collections/photography/numerical-list-of-images/nhhc-series/nh-series/NH-51000/NH-51964.html
In service, the 15-inch gun proved to have a mixed record. On the one hand the 15-inch, firing a 440 pound shot, was able to break the 4-inch armor of the Confederate ironclads which had been designed and built in 1861-1862. In response, the Confederate Navy ceased using their ironclads of the relatively numerous Richmond-class offensively when 15-inch armed monitors were present, and the Confederates would design their next generation of ships (such as Tennessee, Columbia, and Texas) with 6-inch armor, but this stretched the resources of the already iron-poor Confederacy and meant that these subsequent ironclads casemates had to be more compact relative to the size of the ships.
On the other hand the 15-inch gun in the monitors fired quite slowly. Dahlgren himself was very critical of the gun. He worried about how reliable it would be and whether or not it would hold up to repeated firings. He also had concerns about its performance in action. He was in a position to know, by mid 1863 he had left hte Bureau of Ordnance to take up command of the ironclads of the South Atlantic Blockading Squadron. Whereas Dahlgren heaps praise upon his IX and XI inch guns in his autobiography, his comments about the larger weapon are far less positive. This comment about an attempt by the monitors to bombard Battery Wagner “The work of the day acquainted me with some points of the Monitors, the endurance was capital - my own vessel had been struck 67 times but the ponderous XV-inch was too slow in repeating fire - which was its own fault and not that of the Monitor and a fatal defect in hammering earth works, for which rapid fire is needed.” (Dahlgren, John. Autobiograpy. Chapter 4 “Promotion, Command of the South Atlantic Blockading Squadron, and the Siege of Charleston, 1863).
15-inch Dahlgren on display at the Hong Kong Museum of Coastal Defense. This gun was dredged from the harbor of Hong Kong in the 1980s. It is thought to have been part of the armament of USS Catawba which had been sold to Peru after the US Civil War. This photo is © BrokenSphere / Wikimedia Commons and is used under the terms of the Creative Commons Attribution-Share Alike 3.0 Unported license.
XX-Inch Dahlgren Gun intended for the large monitor USS Puritan. Puritan was never completed to its original design. (The monitor built in the 1880s and 1890s was an entirely different ship.) This photograph appears to show the huge Dahlgren mounted in Peru. Detalle - Fotografía Patrimonial (fotografiapatrimonial.cl)
Four 20-inch Dahlgren guns were produced as well - two of which would have armed the monitor USS Puritan. However, that ship was never completed to its original design. At least one was old to Peru, and a picture which may show that gun is above.
Two Bureau of Ordinance 32-pounders of 4,500 lbs on display in Claremont, New Hampshire. Photograph by Wikimedia user Djmaschek used in accordance with the Creative Commons Attribution-Share Alike 4.0 International license.
Two further guns deserve mention in this overview. In 1864 a new 32-pounder weighing 4,500 pounds and an 8-inch gun weighing about 6,500 pounds were introduced by the Bureau of Ordnance. They are clearly created based on Dahlgren’s principles and design, however there is some debate as to whether he should be credited as the designer.
US Navy Bureau of Ordnance 8-Inch Shell Gun of 6,500 pounds displayed in Battery Park in Burlington, Vermont. Note that the cannon is displayed on an original iron Marsilly carriage.
And finally, even though this overview is about smoothbore Dahlgrens, a few of the 11-inch smoothbores were converted in the 1870s to 8-inch rifles. I’ve written about that conversion in this post: https://www.santee1821.net/preserved-artillery/8inch-dahlgren-rifles-at-patriots-point
8-inch Rifle converted from 11-inch Dahlgren Smoothbore on display near Patriots Point Soccer Stadium in Mount Pleasant, SC.
Sources and Additional Reading:
Olmstead, Edwin, Stark, Wayne E., Tucker, Spencer C. The Big Guns: Civil War Siege, Seacoast, and Naval Cannon. Museum Restoration Service, 1997.
Ripley, Warren, Artillery and Ammunition of the Civil War (4th Edition). The Battery Press, 1984.
Schneller, Jr., Robert J. “The Last Smoothbores: The Development of John A. Dahlgren’s Heavy Cast Iron Ordnance for the United States Navy in an Era of Transition, 1848-1865.” Available at: https://americansocietyofarmscollectors.org/wp-content/uploads/2019/06/1987-B57-The-Last-Smoothbores-The-Development-of-.pdf
