Beds for mortars… for a not so quiet sleep

In discussing the seacoast and now the siege mortars, I’ve mentioned the beds on which the mortars were mounted for firing. The high angle of fire for mortars presented problems which necessitated the use of beds instead of carriages. Since the mortar had to elevate at 45° or sometimes higher, the mounting required a range of movement free of any restrictions to elevation. And once the mortar fired, those high angles transferred the force of recoil directly down onto the carriage and against the ground (unlike guns or howitzers with acute angles of recoil). With that recoil angle, the mortar tended to rebound off the ground. To avoid destroying the mounting after a few firings, the beds had to be of solid construction.

In earlier times, mortars used beds build of, in the words of John Muller, “folid timber” (oh, that is “solid timber”… darn 18th century texts and their ‘f’s and ‘s’s). But by the early stages of the 19th century, armies turned to cast iron construction. Recall the bed used on the British mortar now at Fort Monroe.

9 July 2011 275
8-inch British Mortar and Bed

American siege mortars used a similar bed. One of those is on display at Fort Pickens, Florida today, supporting a 10-inch Siege Mortar Model 1840. Let me borrow this photo from Flickr to illustrate:

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10-inch Siege Mortar Model 1840

Alfred Mordecai described the mortar beds in his 1849 Artillery for the United States Land Service:

The beds for 8-inch and 10-inch siege mortars are similar to each other, differing only in their dimensions.

They consist of two cheeks, a middle transom and a front transom, of cast iron, all made in one piece.

Four maneuvering bolts, of wrought iron, are set in the mould, when the bed is cast.

The trunnion bed is accurately reamed, in the cheeks and transom.

Two cap squares, of wrought iron, are fastened to the cheeks, each by two straps held by two bolts passing through holds in the cheeks, and keyed on the outside.

A bolster (oak) is fastened on the front transom by two bolts and two nuts. The bolster has a groove fore the elevating quoin, which is placed in a direction perpendicular to the axis of the mortar.

For firing, the mortar bed sat on top of a wooden platform made of hard wood. By regulation the platform consisted of six sleepers and eighteen deck planks.

The bed for the 8-inch mortar weighed 920 pounds and measured 42 inches by 34 inches. The 10-inch variety weighed 1830 pounds, measuring 51.8 inches by 40 inches. So in terms of weight, the mortar bed weighed about the same as the mortar. Add in the weight of the mortar wagon to transport the setup, and you have a hefty eight-horse load.

Civil War photos show a slightly different bed design with more structure for the cheek plates. One of those appears in the artillery park at Broadway Landing, Virginia at the end of the war. The mortar may be a weapon captured from Confederates, accounting for the differences in the bed.

That crop is from a larger image, one of several showing this rather interesting scene with dozens of cannons. It’s one place I’d like to visit, given a time machine.

At some point, I need to walk through those photos… cannon by cannon… but first the mortars.

Published by Craig Swain

"Historical marker hunter" and Civil War enthusiast.

4 thoughts on “Beds for mortars… for a not so quiet sleep

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