12 pdr Coehorn Mortars

[Western Reserve Volunteer]

No, that's not a misspelling: I recall that the Confederates made some 12 pdr Coehorn mortars during the war, and I attach a picture of a mortar so described elsewhere. It might actually be a later 24 pdr mortar, however. It is from a large trophy cash of weapons at the end of the war.

Presumably the idea here was firstly to utilize existing and common 12 pdr shells, and secondly because the 24 per Coehorn is, as I can personally attest, a pain to try and move around. Movement by four men... yeah right! I seem to remember it took more like eight people to move in actual fact.

Capt / Col. Henry Abbot, 1st Conn Heavy Artillery also stated: "I also think that, like the confederates, we should introduce a 12-pounder Coehorn mortar into our service, which, .... For practice against troops, the 12-pounder Coehorn is decidedly more deadly than the 24-pounder; as its shell, when the fuze burns too slowly, does not bury itself on striking, and the fragments thus scatter widely" in his book on the siege of Richmond. So they seem to have been successful enough to get mentioned as a possible addition or replacement for the existing US Army mortars too!

Interestingly, Abbot also says that he tested using spherical case ammunition, making it experimentally in 1863 in 10" caliber using 12 pdr case shot and a standard 10" shell. The idea was to eliminate the "stone mortar", a specialized mortar which doesn't ever seem to have actually been produced, with most of the Army's examples being captured in the Colonial days, which was designed to fire lots of small projectiles vertically vs horizontally, usually against the attackers of a fort who had managed to make a breech in it's walls, or vice versa. Evidently Abbot was please with the result and put them into use during the siege of Richmond, although he did note that the expedient had problems with premature detonation, he believed because of issues with the wooden fuse and the balls within. He felt that a more regular type of case with the balls suspended in sulfur (!) would have been better.

The question I have is: first of all does anyone have any more information on these mortars? Someone has reproduced one with a "ladder bed" which looks very different to the one shown above, allegedly based upon an original in a private collection.

Also, it is my understanding that prior to the US Army's creation of the M1841 Coehorn Mortar in the 24 pdr caliber, the smaller 12 pdr caliber had actually been the more common size of mortars, especially those originally in service to the British, is this correct? Given the sort of specialized use of mortars as strictly support weapons for assaults in sieges, I imagine the original colonial Coehorns stuck around for a long time: if so, why did the Army then decided to settle on a caliber double the size of the proceeding mortars when designing their replacements? Did they feel the old caliber was too weak for 19th century sieges?

 

[Story]

Why do I seem to remember seeing a line entry for these in the later Bannerman catalog(s)?

 

[Rhea Cole]

Note: indeed, sulphur does, on the face of it, seem like an odd form of packing material.

Spherical case / shrapnel shot consisted of a hollow sphere filled with balls & detonated by a timed bursting charge.

As you can see in this photo, the balls needed some sort of packing to keep them from rattling around & leave the proper space for the fuse / charge.

Sulphur was a Goldie Locks solution. It could be poured in as a molten liquid; when cooled it was hard enough for stability; yet broke apart easily when the case shot detonated allowing the balls & shell fragments to scatter.

 

[Western Reserve Volunteer]

This cutaway also does a great job of explaining what the issue with the fuses was: apparently the mortars were still using the old wooden plug fuses, and trying to cram a fuse into a the extemporized shells with balls in them was what was causing the issues, that and that apparently the only packing material was the powder in that case. I think on reflection the men were probably more right than he was in saying it was actually the balls rattling around and setting off the bursting charge prematurely that was the issue.

I imagine that the commonality with the 12 pdr caliber would have also been a boon because it allows for the use of the more sophisticated Boreman and other fuses. It's kind of weird that the larger mortars were apparently so behind the curve on this.

On the subject of shells: apparently the Confederates also worked out that if you cast the interior of a shell as a polyhedron then when it bursts the fragments are evenly sized.

 

[Western Reserve Volunteer]

I have determined that the picture in the first post is in fact of a Confederate 24 pdr Coehorn. I believe the "ladder" carriage type I previously mentioned is the original form of the Confederate 12 pdr Coehorns which makes a great deal of sense as they must have been calculated for being lighter to carry.

 

[Story]

Sulphur burns around 450°F with a bright blue flame and since gunpowder burns hotter than that, the resulting shell explosions must have been remarkable.

 

[Story]

The idea was to eliminate the "stone mortar", a specialized mortar which doesn't ever seem to have actually been produced, with most of the Army's examples being captured in the Colonial days, which was designed to fire lots of small projectiles vertically vs horizontally, usually against the attackers of a fort who had managed to make a breech in it's walls, or vice versa.

aka https://en.wikipedia.org/wiki/Fougasse_(weapon)

A fougasse was successfully used on October 22, 1777 by the defenders at Fort Mercer (NJ) to blunt a Hessian assault, specifically at the fort's front gate. This one was dug into the ground, much like those found at Malta.

 

[Story]

This thread made me curious enough to wander off at lunch and see what answers might be out there.

MHG1012 COEHORN 12 POUND MORTAR [A] - Merz Antique Firearms

Very similar to US 1841 style mortar. This is unmarked and made by Dutch military engineer Menno Van Coehorn early in the 18th century. A very interesting item. Designed with iron handle bars so that two men could move it along in the trenches. Made of 3 inch heavy thick planks 24 Inches by 13...

www.merzantiques.com

Interesting about the tong holes

12-pounder CS Coehorn Mortar

Civil War Artillery Projectile Site. Photographs and descriptions of over 170 Civil War Artillery Projectiles.

www.civilwarartillery.com

I'm surprised @Dan Kohli hasn't referenced his own observations in this thread.

The Coehorn Mortar; were they effective weapons? | Cannons / Artillery & Crew Served Weapons

When compared to cannons, mortars are cannon's short fat brothers. Mortars were not modern concept and had been around since the 1600s. Still mortars saw plenty of use during the Civil War. They are simple and rugged and fill a necessary need. Mortar's plunging shells are useful for...

civilwartalk.com

 

[Rhea Cole]

Since a 12 pound Coehorn mortar is the subject of this thread , I am posting 3 links. Two of them are… eccentric.

Let me preface this with the fact that feral cats are a serious threat to wildlife, especially birds. It is legal, encouraged even, to hunt them. That being said, there hunting & then there is hunting..,

"How to hunt Wisconsin feral cats with a 12 pound Coehorn mortar cannon."

Link:

COEHORN MORTAR

Coehorn Mortar Hunt for Wisconsin Feral Cats. How to Hunt with a Coehorn Mortar. Build a Civil War Mortar.

www.buckstix.com

While I am (chose one) amusing, disgusting, astounding you, might as well go alll the way.

"Hunting Wisconsin White Tail Deer With a 12 pound Mountain Howitzer."

To those who chose amused above: Fair warning, this written in a droll manner… a friend spit milk & sugar coffee onto his keyboard with unfortunate effect.

Link:

MT. HOWITZER

HOWITZER HUNT - Mountain Howitzer Cannon Whitetail Deer Hunt and build your own 12 pound Mountain Howitzer Cannon.

www.buckstix.com

Considerably less gruesome, the NPS Coehorn mortar drill manual is based on actual practice. Nobody wants to be in close proximity forward of the muzzle of a black powder weapon. 60% of the volume of the charge is expelled as particulate. That is why it here is so much white powder smoke.

After a CWT member questioned the NPS drill I post on a thread, I asked the editor of the NPS Historic Weapons Manuel about it. With a few minor tweaks to enhance safety, the NPS drill is historically accurate. Safety first is our mantra.

Link:

https://npshistory.com/publications/battlefield/hwp/coehorn-mortar-demos.pdf

 

[James Brenner]

Ladder bed?

 

[7thWisconsin]

Because the barrel is sooooooooo short, the blast from a coehorn is truly fiercesome. It´s like having someone physlcally push you backwards.

 

[Western Reserve Volunteer]

aka https://en.wikipedia.org/wiki/Fougasse_(weapon)

A fougasse was successfully used on October 22, 1777 by the defenders at Fort Mercer (NJ) to blunt a Hessian assault, specifically at the fort's front gate. This one was dug into the ground, much like those found at Malta.

Yes something similar in concept to a fougasse, but instead of extemporized in the form of a proper mortar, with a small powder chamber and a exaggerated mouth.

 

[Rhea Cole]

Because the barrel is sooooooooo short, the blast from a coehorn is truly fiercesome. It´s like having someone physlcally push you backwards.

I agree, the drill has a run for your life air about it.

 

[Western Reserve Volunteer]

This shows the form of the never produced M1841 stone mortar. Earlier models were actually used, mostly of originally European designs. They were quite specialized and rare!

 

[Rhea Cole]

Not mentioned in these amateur standings..,

This a a breechloader…

The lowest man on the totem pole must have touched this monster off. Notice the mortises surrounding the muzzle & breech. They are for locking on & twisting the breech on & off. You have to wonder what the rate of fire was.

Hôtel des Invalides, Paris, France

 

[Western Reserve Volunteer]

This is the replica of the 12 pdr CS Coehorn I was mentioning earlier.

You can see what is meant by "ladder bed" here. The original it is based on is apparently in a private collection, so it's hard to vouch for the accuracy of the reconstruction. But it seems plausible enough, and would presumably be lighter than an equivalent solid wood bed.

 

[Western Reserve Volunteer]

Not mentioned in these amateur standings..,
View attachment 527707

This a a breechloader…

View attachment 527708
The lowest man on the totem pole must have touched this monster off. Notice the mortises surrounding the muzzle & breech. They are for locking on & twisting the breech on & off. You have to wonder what the rate of fire was.

Hôtel des Invalides, Paris, France

With a bombard like that, I imagine the screw-together construction is more of an adaptation for easier transport to a siege. Probably it was still a muzzle loader. Those things were huge!

 

[Rhea Cole]

With a bombard like that, I imagine the screw-together construction is more of an adaptation for easier transport to a siege. Probably it was still a muzzle loader. Those things were huge!

According to what I read (albeit in French) the powder was loaded into the breech & screwed on.

This example not only shows the threaded breech, you can clearly see the banded construction. That was when blacksmiths were mighty men! No trunnions… how did that work?

All this is a few hundred years outside my expertise. I speak fluent Spanish & can read military & art history French pretty well.

 

[Western Reserve Volunteer]

If the French say it is then it must be so! I wish I were better at languages… I have only a smattering of rudimentary Japanese, on a good day with a following wind!

Bombards are also a little outside my expertise as well…

 

[1st Section]

Considerably less gruesome, the NPS Coehorn mortar drill manual is based on actual practice. Nobody wants to be in close proximity forward of the muzzle of a black powder weapon. 60% of the volume of the charge is expelled as particulate. That is why it here is so much white powder smoke.

After a CWT member questioned the NPS drill I post on a thread, I asked the editor of the NPS Historic Weapons Manuel about it. With a few minor tweaks to enhance safety, the NPS drill is historically accurate. Safety first is our mantra.

Link:

https://npshistory.com/publications/battlefield/hwp/coehorn-mortar-demos.pdf

"Historically accurate" for the 18th century perhaps, but not particularly relevant to the study of mid-19th century usage. For anyone interested in loading and firing Civil War mortars please refer to "Instruction for Heavy Artillery" as adopted by the War Department in 1851, revised in 1862, and reprinted in both the north and south. Even a cursory glance between the original text and the NPS document will show they have few similarities.