Fortification Friday: More magazines… coffer-work, gabions, and splinter proofs

Last week, we took a look at the form and function of powder magazines in field fortifications.  Magazines protected ammunition – both from enemy action and natural agents (moisture being the most dangerous in that regard).  We also saw that, in field fortifications, would be constructed of fascines, coffer-work, or gabions.  Having looked at the first of those construction types, let us turn to the coffer-work.  Briefly, the coffer-work was a magazine lined with boards, planks, or what have you, instead of facines.  But the details of construction differed, of course:

A coffer-work is formed by making frames of six-inch scantling; each frame is composed of two uprights, termed stanchions, and a cap and ground-sill, will nailed together; it is six feet wide, and six feet high in the clear.  These frames are placed upright, and parallel to each other, about two-and-a-half feet apart; they are covered on the top and sides by one-and-a-half-inch plank, which is termed a sheeting. The magazine otherwise is constructed as in the last case.

We have two elevations illustrating the coffer-work.  First a longitudinal view:


And a cross-section:


As with the fascine magazine, we see the basic dimensions set with a six foot wide floor and a six foot height.  We might relate the coffer-work to the internal finishing of a room. We see a framing (stanchions) with studs 2 ½ feet apart.  A floor and walls made of planking laid over that. Note the planking… I mean sheeting… also nailed in place for the ceiling.  A roof consists of two layers of fascines along with the appropriate amount of earth atop that.

Two fine points on the layout.  First is the sill.  This was dug out prior to laying the stanchions.  The longitudinal view bisects the magazine.  So giving the visual impression the floor floats in thin air… not so, just correlate in your head to the cross-section.  Also note the sill slopes to the entrance, as specified. Also note that instead of slanting outward and upward, the coffer-work’s walls are straight.  6x6s are sufficient to hold back earth against more than the natural slope.

Bottom line, the materials used for the walls and the slope of those walls was the main difference between fascine and coffer-work magazines.  Likewise, when using gabions, the chief difference is again how the walls are built, but the materials demanded a different approach to the construction work:

When gabions are used, a hole is usually dug in the ground to form a part of the magazine; the gabions are placed in two rows, side by side, around the hole, and are filled with earth. The top is formed as in the case of fascines.

Turning to the next figure:


Yes… it is crooked in the original and fixing it detracts from the detail.   And.. we are missing some detail as it is!

Gabions are great if one is reinforcing walls, as we discussed in regard to revetments. But there are limits to gabion load bearing.  Instead of a wall completely constructed with gabions, the trick is to cheat a bit – dig a three foot (or so) trench so the gabions need only be three foot tall.  Double stacking gabions or six foot tall gabions would be a weaker structure.  Missing details in the figure include the floor, any revetment of the lower half of the walls, and the earth laid against the exterior of the gabions.  Based on “in the case of fascines” there should be a sill, a floor of planks, and perhaps fascines over the lower half of the walls.

The gabion magazine looks attractive.  I can easily relate experiences where similar shelters are built using the modern equivalent to gabions.  But Mahan seemed to prefer fascines and coffer-works over gabions for magazine construction.  Clearly the choice between the types would be weighed against resources and practicality.

So three types of magazines to consider.  But we have a natural weak point to address – the mouth, or doorway.  Must have a mouth open to allow passage.  And that passage will let in messy things like enemy shells.  How to fix that?  Splinter-proofs!

The mouth of the magazine is covered by a splinter proof shelter.  This is constructed by taking scantling eight by ten inches, cut into suitable lengths, and placing it in an inclined position, so as to cover the mouth, and leave an easy access to it. The pieces, usually, are inclined 45º, and are placed side by side; they are covered by at least two feet of earth, or sods; and hides or tarpaulins are thrown over the whole.

Splinter proofs looked as such:


As described, 8x10s lain against the magazine’s exterior wall.  Two feet of earth on top of that.  And a tarp anchored at the top and lain over the whole.  Notice also the fascines as a revetment of the exterior wall of the magazine (on the right) and the elevated flooring (bottom).  Keep in mind the amount of foot traffic expected through the splinter proof.  The layout had to protect but allow passage.  Passage, that is, of men carrying heavy artillery projectiles and such.  So select the good timbers for the floor.

But, as the name implied, splinter proofs offered less protection than bomb proofs. Yet, lesser protection was deemed sufficient for some uses within the fort:

 Splinter proof blinds are mainly intended to afford a shelter against the fragments of hollow projectiles that explode in the work.  They may be used as a kind of barrack for the troops; and to store provisions, &c.

For example, splinter proofs appeared all across Morris Island during the summer of 1863. Those were used as staging shelters for infantry, sappers, and engineers working on the siege lines.

So we have the specifications for the magazines to include protection of the entrances.  But not so fast.  Writing post war, Junius Wheeler had some refinements, to include references to wartime practices.  We need to examine those instructions if we wish to understand the practice, as applied to magazines, used during the Civil War.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, page 59.)

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