Hauling the Siege Mortar: the Mortar Wagon

In the previous mortar post, I mentioned the mortar wagon used for siege mortars. At first glance, this piece of equipment makes perfect sense. But allow me to elaborate on what is common sense, just in case something is a little unclear.

Mortars, because of their high angle fire, did not work well with wheeled carriages (and only in modern times with steel components and pneumatic recoil systems have mortars taken to wheeled carriages). The angle of the recoil force could strain axles. Further the “rebound” off the ground further strained the entire carriage. So mortars used beds instead of carriages. I’ll examine the beds in more detail later, but for now let’s just consider them ground mountings for the mortar.

Without wheels, mortars on beds presented a mobility problem. To allow them to follow the field army, the mortars rode on wagons. And not just any wagon… but a mortar wagon!

This diagram, from the 1851 edition of Instructions for Heavy Artillery, depicts the wagon, sans mortar, and its limber. The limber was the same used for siege gun and mortar carriages. The mortar rode between the upright stakes on the wagon. Seen from above, the wagon’s planks and side rails provided ample space to carry the mortar. Note the cross piece at the back of the wagon (on the right). That is a roller (or windlass) to aid handling the mortar or other cargo.

John Gibbon provided particulars of a standard mortar wagon in his 1860 Artillerist’s Manual. The wagon was just under 12 feet long. The “floor” of the wagon, on which the mortar rode, was 63.85 inches by 40 inches. With the limber that increased to 24 feet. Complete, the wagon and limber weighed 3185 pounds.

Although the wagons were designed for mortars, they could carry other cannons or cargo when needed. The manuals do not detail the maximum payload for the wagon. However the mortar wagon used an eight horse team, if one wishes to estimate the theoretical weight limit based on motive power.

So how did the crew heave those heavy siege mortars onto the wagon?

The crew started the operation by elevating the rear of the mortar bed, using blocks, baulks, and rollers. The crew then placed stock of the wagon (the middle rails that later would mate with the limber) under the elevated mortar bed. Using ropes attached to the windlass, and anchored to the maneuvering bolts on the bed, the crew pulled the mortar onto the wagon. I’m fond of the description found in the Instructions for Heavy Artillery for this part of the operation:

Nos. 1, 2, 7 and 8 heave upon the windlass, and Nos. 9 and 10 press against the rope with the handspikes of Nos. 1 and 2 to prevent its turns spreading too much upon the roller. Nos. 5 and 6 urge the mortar up until it is ascending the stock; they then place the butt ends of their handspikes upon the stock, and follow up the movement. Nos. 3 and 4, aided by Nos. 5 and 6 with their handspikes, shift the rollers, and chock them whenever necessary.

And after much “urging”… and perhaps much swearing … the crew pulled the mortar and bed up to the back of the wagon. From there they raised the stock and attached the limber. The crew stowed the mortar, ensuring it was fixed with chocks, spikes and ropes. At that point the mortar, bed, and wagon were ready for the horses.

Dismounting from the wagon followed the reverse process, using the windlass to lower the mortar bed down the stock. Of course, with something so heavy, the battery officer was supposed to ensure the mortar got to its firing position without a lot of handling and maneuvering.

Sounds like a lot of work just to heave a shell onto an enemy fortification. But in its time, these were the preferred means to batter down defenses. A field army might not have many of these siege mortars, or even need them on a day to day basis. However when the open maneuver turned to siege, better to have those wagons and cargo than not.

Published by Craig Swain

"Historical marker hunter" and Civil War enthusiast.

3 thoughts on “Hauling the Siege Mortar: the Mortar Wagon

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