Rodman Heavy Artillery

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Here at Firearms Talk, we usually talk about portable hand cannons and shoulder fired weapons only. However from time to time we do cover what can be referred to as heavy artillery. There is one piece of remarkable US military hardware that fits the bill of 'heavy artillery' like none other-- the Rodman.

What is a Rodman?

Ever seen that comical 'cannon' that the circus performers shoot acrobats out of? Well, if you were to make a real one out of cast iron, you would have a Rodman. Thomas Jackson Rodman was a Union artillery officer and engineer who came up with a radically different way of making large guns. Until 1861, most large cannon were cast in one huge block of iron and then drilled out. This made the gun prone to developing cracks that could (and did) break apart the entire gun over time. Rodman invented a method of hollow casting the gun in layers using water constantly pumped over the metal to cool it. This made large and strong cannon that dwarfed the older cast guns. They are identified by thier characteristic coke-bottle shape and flat cascabels (rear).

Rodman Heavy Artillery - christophereger - rodman-gun-va-867.jpg

15-inch varieties

These beasts are the most common of all of the heavy Civil War era artillery. These giant coastal guns could be added to a simple wood and earth battery to give it the strength to sink even the most modern ironclad warship of the day. In terms of hardware, 40-pounds of cannon-grade black powder was exploded inside the breech to 25,000psi in the chamber and could send a 400-pound piece of steel shot some 20,000-feet (3.5-miles) with reasonable accuracy. The shells could penetrate up to 10-inches of iron railway type armor. These guns were the reason for the "3-mile limit" in claiming US coastal waters of the time. These amazing iron cannon weighed more than 25-tons or about the weight of 14 Jeep Wranglers and took a 12-man crew to operate. Some 323 15-inch Rodman's were built between 1861-1871. They were installed at masonry coastal defense forts all along the entire 12,600-miles of US coastline during the last half of the 19th century.

Rodman Heavy Artillery - christophereger - cannon-remains-1908-868.jpg

The advent of modern rifled naval cannon of steel construction doomed these giant beasts to the scrap heap by the 1900s. They were broken up with explosives, cut apart, melted down, and done away with. By twist of fate, only 25 remain today, mainly at offshore forts like Fort Taylor in the Florida Keys and Fort Massachusetts on Ship Island. These in most cases were too expensive for scrappers to move. The National Park Service however is trying to save some of these heavy bruisers and is even trying to remount some of these in any way they can.

Although born in the middle of the greatest war on the continent, these gentle giants were never fired in anger.

Besides the 323 15-inch Rodmans made, some 213 smaller 8-inch and 1301 10-inch versions were produced during the Civil War of which over 150 remain on display around the country. There were also a couple Rodmans that were larger than the 15s.


Rodman Heavy Artillery - christophereger - building-a-20-inch-rodman-870.jpg

In 1864 Rodman moved on from his puny 15-inch design to something slightly bigger-- a cannon with a bore of 20-inches wide. For those of you that talk in millimeters, that's 506mm. This beast weighed 58-tons and was over 20-feet long. The 20-inch Rodman's were the largest bore cannon ever used by a military in the Western Hemisphere, the largest bore cannon ever used by the US military of any era, and the largest muzzleloading cannon ever forged on US soil.

Four were made, one of which for sale to Peru (which disappeared in 1881). One was mounted at Fort Hamilton, New York, another at Fort Hancock, NJ and are still there on display today. The fourth, a shortened piece, was to be mounted on the never commissioned "super monitor" USS Puritan. Packed with 200-pounds of black powder, they could fire a 1080-pound piece of steel shot over 8000-yards. These huge cannon were only fired 8 times in peacetime practice and never in war.

Now that's heavy artillery

Rodman Heavy Artillery - christophereger - 15-rodman-869.jpg
Surviving 15 Inch Rodman at Fort Massachusetts -- note the circular iron tracks allowed the cannon to be turned to fire in any direction. (photo by TradigiAnne via Flickr)

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November 4, 2012  •  02:45 PM
Very interesting.
November 22, 2012  •  09:42 PM
Great article! Thanks for the articles that you keep pouring out.
March 1, 2013  •  01:40 PM
I'll take 2
March 5, 2013  •  04:48 PM
I tried inserting a recent pic of the 20" Rodman outside Fort Hamilton, Brooklyn, NY, with a Navy Corpse-Man (as Commander-in-Chief Obama renamed them) buddy of mine next to the huge thing (w/cannon-balls to its left). The other 20" gun made was, and is, on the other side of the entrance to NY Harbor, waiting for British warships as well. Well, not as much today... But during the US Civil War the UK was threatening to intervene which meant invading the North!
August 18, 2013  •  05:01 PM
makes me wonder if Senator Fienstein (sp) would want to allow a magazine or "clip" for this one.
May 1, 2017  •  10:15 AM
What was revolutionary, at the time, about Rodman's casting process was not only using water to cool the cast iron after pouring into the casting mold, but a cooling core that was placed inside the bore itself during the casting process. This unique method allowed for a more rapid and even cooling of the cast iron and reduced or prevented the formation on gaps and pockets in the cast iron that occurred routinely with the earlier outside-only cooling of cast iron cannon castings. Those voids quite often resulted in reduced lifespan of the guns, and occasionally caused a catastrophic failure of the gun while the gun crew was firing them.