Mounting and moving the little Coehorn Mortar

Earlier I wrote about the origin and design of the Coehorn mortar in American use and promised to look at how the weapons were mounted and transported. Because the Coehorn’s small size it’s a popular subject for those who want to own their own artillery. For a few thousand bucks, you can field your own siege train. And if I may be allowed an event plug, you can watch some of those little mortars fire at the N-SSA National Skirmish starting today through October 7 at Fort Shenandoah.

Suffice to say there are plenty of patterns and blueprints for the Coehorn beds out there for those interested. I’m more interested in the variations in the patterns. By regulation, the Coehorn bed was 31 inches long and 15 inches wide. It weighed around 132 pounds (adding to the 160 pounds of the mortar itself). In his Artillerist Manual, John Gibbon described the bed as:

… made of a block of oak wood, in one piece, or two pieces joined together with bolts. A recess, for the trunnions and part of the breech, is made in the top of the bed; and the trunnions are kept in their places by plates of iron bolted down over them. Two iron handles are bolted to the bed on each side, by which four men can carry the bed with the mortar in its place.

Not very complicated. Again, turning to one of several on display at Peterburg National Battlefield, here’s an overhead view:

Petersburg 4 Mar 12 185
24-pdr Coehorn, Alger #33

Clearly not much to it. The use of wood as the major component is also a variation from the practice with larger mortars. With the low powder charges – ounces of powder – the Coehorns did not exhibit the severe recoil of the larger mortars. Notice there is no elevation mechanism. Not even a wedge or quoin. The Coehorn mounting fixed elevation at a 45° angle. More on that when I discuss the operational use of the mortar.

The reproduction bed at Petersburg, like that at Cold Harbor, has a curved – perhaps “fitted” is the word – front and rear face.

Seven Days 26 May 12 170
24-pdr Coehorn, Ames #154 at Cold Harbor

That seems to be the basic profile used by the U.S. Army. Sort of makes sense, as it eliminates boxy edges in the areas where the crews are most likely to be working. But wartime photos indicate there were some variations in the profile. Let me turn back to those wonderful photos taken at Broadway Landing at the end of the war. Looking at the row of Coehorns seen in the back of the photos, there’s at least three distinct bed patterns visible:

Yes, three different variations in a nice row, almost as if posed for the photographer. You can even make out the split of the two halves of the beds. But there is also a fourth bed variation in the same photo:

That’s an iron Confederate Coehorn… and a segue into another post. As you can see the Confederates didn’t shave off the ends of their beds. And they didn’t waste any paint on the bed either. The iron handles and straps are there just as on the regulation beds.

As Gibbon mentioned, four men could carry the 300 pounds of mortar and bed around the battlefield and into the siege trenches. Figure on a 75 pound work load on each crew-member. Some sources say two men could move the mortar in a pinch. (150 pounds? I’d have petitioned for more pay if it were me.)

Clearly for longer moves, the crew wouldn’t carry the mortar by hand. John Tidball’s Manual of Heavy Artillery Service (1884 edition) indicated the crew placed the Coehorn on a wagon – or better still an ordinary field caisson along with two ammunition chests:

The mortar is carried on the caisson body, the front chest being removed for this purpose. The piece is securely lashed with ropes through the handles. The remaining ammunition chests are arranged to carry thirty shells each. The powder is in cans, and a set of measures (from one to six ounces) should be provided. The shells should be charged and fuse-plugs driven, ready for the insertion of the fuses.

Additional caissons carried more ammunition chests as needed.

Charged shells with fuse plugs driven? Yep, that’s loaded and ready for serious work. Such alludes to the Coehorn’s 20th century equivalent – the infantry mortar … and that weapon’s employment on self-propelled platforms.

US Mortar team

Now that I have XBrad’s attention…. maybe in concept, but the Coehorns could not be fired while on the caissons, as I don’t think the horses would be too happy. But the 81mm mortar seen on this World War II half-track was working the same basic function – high angle fire support – and could fire from its transporter. And as you can tell from the “stuff” tied off all about, the crew didn’t have to dismount either. I wonder what Gibbon and Tidball would say about that!

Let me turn next to how the crews used those little Coehorns (and then talk about the Confederate versions).

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