Mortars for the Army and Navy

One-hundred and fifty years ago this month, operations on several fronts in the Civil War featured the use of a new pattern weapon.  Both the Army and Navy brought 13-inch mortars to battlefields such as Island No. 10 and Fort Pulaski.  Later, in April, the heavy mortars appeared on the Virginia Peninsula aimed at the defenses of Yorktown.  From that point on, the 13-inch mortars played a prominent role in the war effort along the coasts and in many siege operations. Their employment at locations from the Mississippi River to Petersburg ensured the 13-inch mortar a place among the most important weapons of the war.

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13-inch Seacoast/Sea Mortar at Fort Moultrie

As I have somewhat neglected this class of weapons, allow me to belatedly introduce the mortar, as it was used in the 19th century, before discussing the 13-inch and smaller brethren in detail.

The mortar concept dates back to ancient times, arguably before black powder cannons.  The idea was to loft a projectile at high angles, over any obstruction, on top of the enemy defenses. Typically mortars fired shells, but solid shot, grape-shot, and incendiary projectiles found their way into the muzzles of these short cannon.  By the time of the American Revolution, the mortar was part of every respectable artillery park.

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Colonial-era Mortar at Yorktown

As with guns and howitzers, different calibers and classifications existed to meet an array of tactical requirements.  For my purposes of cataloging and categorizing, I divide the mortars of the age into the following classifications:

  • Field or “ultra-light” mortars, often called “Coehorns” although the true Coehorn was only 12-pdr caliber.
  • Siege and garrison mortars, considered “light” in the contemporary sources.  And these were “light” in the subjective sense of the word.
  • Seacoast mortars intended to drop high angle fire on enemy ships.  These were considered “heavy” in the ordnance manuals.
  • Naval or sea mortars used afloat for bombarding enemy defenses (in other words countering the seacoast mortars mentioned above).
  • An “other” category for stone mortars, experimental types, and non-weapons like the eprouvette.

Starting with the smallest, Menno van Coehoorn developed a light mortar in the 15th century as a practical answer to well-built fortifications.  Carried by four or five men, Coehorns were small enough to move right up to the forward siege lines or even with a field army. Traditionally Coehorns were 12-pdr caliber.  But the US Army standardized a bronze 24-pdr Coehorn weighing 138 pounds in 1838.  Other weapons used during the Civil War in the “Coehorn” classification include Confederate 12- and 24-pdr cast iron models.

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24-pdr Coehorn... at my feet!

Siege and garrison mortars, much like guns of the same classification, were larger weapons almost exclusively made of iron.  The siege mortars reduced enemy fortifications in conjunction with guns and howitzers.  Or conversely provided counter battery fire for those defending forts.  These were typically 8- and 10-inch calibers.  A handful of survivors and a limited paper trail indicate the Army, state, and militia organizations purchased several 10-inch weapons between 1812 and 1839.  Between 1839 and 1840 the Army established production patterns, receiving 41 of the 8-inch and 98 of the 10-inch Models of 1840.  As with all ordnance, the mortars went through a design change for the patterns of 1861 resulting in a cleaner profile.  Filling wartime production contracts 170 8-inch and 150 10-inch Models 1861 came from northern foundries.

Fort Macon, NC - 10 In Siege Mortar Model 1861
10-inch Siege Mortar at Fort Macon, NC

Like the Siege mortars, seacoast mortars were iron weapons.  The seacoast mortars also followed a similar design history as the siege types, starting with early 10-inch models.  In 1840, the Army approved a 10-inch seacoast mortar.  Only ten were accepted prior to 1860, but West Point and Cyrus Alger produced over twenty more in the early ears of the Civil War.  Experimental 12- and 13-inch seacoast mortars produced in 1840 properly fit in the last category mentioned above.  With the establishment of new patterns in 1861, the Army authorized production of 10- and 13-inch seacoast mortars.  Alger produced eight of the former.  However, as noted above, the larger seacoast mortar was produced in quantity and well used.

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10-inch Seacoast Mortar, St. Augustine

Naval use of mortars prior to the Civil War was limited.  While operating against the Barbary pirates the Navy purchased some 13-inch English mortars for use bombarding shore defenses from aptly named “bomb” vessels.  Smaller mortars appeared from time to time on ships, but the 30 second flight time of the projectile limited their use in ship-to-ship combat.  Shore bombardment, either along the coasts or on the rivers, became a major component of the Navy’s operations during the Civil War.  To fill the role, the Navy purchased a large number of the Army’s 13-inch seacoast mortars for use afloat.  There was no significant difference between Army and Navy weapons. Indeed, in many cases Navy weapons were inspected by Army personnel at the foundry.

13-inch "Old Abe" Mortar on the USS C.P. Williams

Stone mortars are an oddity of sorts.  In the colonial era, these functioned as anti-personnel weapons during siege operations.  With oversize bores (between 13 and 20 inches), these mortars fired baskets full of stones, or in some cases shells. While useful for concentrations of infantry – say at the point of a breech – the weapons had little use in the broader spectrum of combat.  Yet several of these remained at forts around the American coast.   The US Army produced two bronze stone mortars before the Civil War.  But all references I’ve seen to those calibers during the war relate to ancient colonial-era artifacts caught up in the war.

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Large mortar at Yorktown - Matches Stone Mortar descriptions

So the mortar formed a small, but important, part in the American artillery inventory before and during the Civil War.  The mortar’s contributions reach back to the siege of Yorktown in 1781… then extend to the siege of Yorktown in 1862:

13-inch Mortars at Yorktown

In past posts, I’ve briefly discussed the early 10-inch mortars and the “wooden” mortars of Vicksburg.  Having mentioned the weapon’s important role in the Spring of 1862, I’ll spend a few posts on the 13-inch mortars.  Then turn to the others as time permits.

The Dictator at Petersburg
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