Mortars to knock down walls: Siege Mortars in Pattern of 1840

In last week’s “cannon” post, I drew attention to a British mortar captured during the War of 1812. During the early years of the United States, mortars were not high on the list of ordnance procurements. In the past, I’ve mentioned the rather large number of colonial era weapons surviving today. That alludes to even larger quantities of mortars inherited during the Revolution and subsequent national expansions. Although a few American-made survivors prove there were at least some mortars manufactured between 1818 and 1849, the total must have been small.

In 1839, in conjunction with reforms to the artillery system (which I discussed in more detail in reference to the 6-pdr guns), the Ordnance Board called for a formal pattern of 8- and 10-inch siege mortars. Such weapons, just as that British mortar, were designed to follow behind the field armies in the siege train. When needed, those heavy mortars would form the battering power to reduce an enemy’s fortifications. Sort of a limited role, to be sure, but at the time a necessary component for any army.

As with other weapons under development (or shall we say “refinement”) the Army ordered samples from the gunmakers of choice. Columbia Foundry, in Washington, D.C., and West Point Foundry, in New York, each delivered a pair of mortars in 1839. Both foundries produced one 8-inch and one 10-inch mortar. Records show the Columbia 8-inch mortar weighed 920 pounds, compared to 907 for its West Point rival. The Columbia 10-inch mortar also outweighed the West Point weapon of the pair – 1560 pounds to 1526 pounds. Although the Columbia mortars broke during the tests, apparently the results were sufficient to establish production patterns.

So in 1841, the Army issued contracts for both 8-inch and 10-inch siege mortars with the pattern of 1840. For simplicity, I’ll just refer to those as “Siege Mortars, Model 1840.” The new pattern mortars weighed more than the test weapons of 1839. The table below compares those siege mortars with larger seacoast mortar patterns established around the same time (see note below about sources for this data).

Notice the significant size difference between the two classes, particularly between the 10-inch models. Since seacoast mortars were designed for fixed defenses, not intended to move anywhere fast, these weighed significantly more and could handle larger powder charges. With of course an increase in range.

Unfortunately, I don’t have ample photographs of surviving siege mortars. So the line drawings will have to suffice for now.

Model 1840 Siege Mortar Diagram

Cyrus Alger of Boston produced most of the siege mortars. The firm delivered twenty of the 8-inch mortars in 1842. Alger delivered ten 10-inch mortars at the same time. West Point produced one 8-inch and five 10-inch siege mortars at about the same time. Such numbers were sufficient for the Army’s “siege train” at that time. Ordnance reports indicate at least a dozen of the 10-inch mortars saw active service in the Mexican War. Perhaps as part of the war-time procurement, the Army ordered fifteen more 10-inch mortars in 1846-7 from Alger along with ten more from West Point.

In the late 1850s, the Army placed orders for more siege mortars. Before the two sides exchanged shots at Fort Sumter, West Point delivered five more 8-inch and five 10-inch mortars – all inspected by future Confederate General Benjamin Huger. After the start of the war, deliveries continued with West Point adding four more of each caliber. Fort Pitt Foundry commenced production at the same time, adding eleven 8-inch and forty-nine 10-inch mortars.

Detail of photograph of Broadway Landing, Rich...
8-inch Siege Mortar at Broadway Landing in 1865

But production of the Model 1840 types ceased in April 1862 and shifted to the updated patterns established for 1861. The table below compares the siege mortars of the two different established production patterns.

Notice the weight increase with the 1861 patterns.

And speaking of those “pounds”, consider that weight in comparison to the field artillery of the time. A 6-pdr gun with carriage weighed around 1800 pounds; a 12-pdr “heavy” field gun 3000 pounds; a 12-pdr “Napoleon” roughly 2350 pounds; and a 24-pdr field howitzer at 2450 pounds. A 12-pdr siege gun, also found in the siege trains, on its carriage weighed 5750 pounds.

An 8-inch Siege Mortar, Model 1840 with bed weighed 1850 pounds. The 10-inch Siege Mortar, Model 1840 on its bed weighed 3630 pounds. The beds had no wheels. The weapon, mortar and bed, rode on a mortar wagon to the designated location of employment, which added an additional 3000 pounds. In the next post on these mortars, I’ll examine the beds and mortar wagon in a bit more detail. And as time permits discuss how the crews handled these heavy weapons.

Today five of the 8-inch and sixteen of the 10-inch Siege Mortars, Model 1840 survive.


Aside from on site notes and links provided above, sources consulted for this post were:

Birkhimer, William, Historical Sketch of the Organization, Administration, Material and Tactics of the Artillery, United States Army. Washington: James J. Chapman, 1884. Particularly pages 275-9 discussing the evolution of the American systems of artillery.

Olmstead, Edwin, Wayne E. Stark, and Spencer C. Tucker. The Big Guns: Civil War Siege, Seacoast and Naval Cannon. Alexandria Bay, NY: Museum Restoration Service, 1997.

Ripley, Warren. Artillery and Ammunition of the Civil War, 4th Edition. Charleston, S.C.: The Battery Press, 1984.

Data for the tables assembled from:

  1. U.S. War Department, The ordnance manual for the use of officers of the United States Army (Philadelphia: J.B. Lippincott & Company, 1862), page 18.
  2. U.S. War Department, Instruction for heavy artillery (Presses of Evens & Cogswell, 1861).
  3. Tidball, John C., Manual of Heavy Artillery Service (Washington: J.J. Chapman, 1884), pages 145-166.
  4. Olmstead, et. al., Appendices C117, C118, C145, C146, C163 and C164; Pages 238-9, 254-5, and 260-1.

Published by Craig Swain

"Historical marker hunter" and Civil War enthusiast.

10 thoughts on “Mortars to knock down walls: Siege Mortars in Pattern of 1840

  1. I have a photo probably from the 1850s of a woman beside what appears to be a siege mortar in the pattern of 1840, likely a 13 inch Seacoast. I would like to send a jpeg to you to see if you could identify the mortar and/or the fort. It might be English rather than American. Just email me and I will send the image. Thanks so much for your help.

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