Fortification Friday: Gabionades? Let’s get between the guns!

We’ve spent several installments discussing the evolution of shelters through, and after, the Civil War.  Before the war, Mahan gave the subject just under two pages in the manual.  By the 1880s, Wheeler would allocate a dozen pages to the topic.  And this did not reflect the introduction of any great technical advance in the art of fort-building.  Rather it reflected, in my opinion, specifically changes in the manner artillery was employed… but generally towards changes at the operational level.  But keep in mind, this “change” was more so a heavier allocation of ink in the manuals, which translated to different practices being taught to cadets… in turn translating, when that cadet pinned on lieutenant or captain bars, to the soldiers’ work priorities.

A similar evolution, reflected in the ink of the manuals, occurred with respect to the protection used within the batteries, between the guns. These were technically traverses. The intent was to provide safety to the gunners from enfilading fires. Before the war, Mahan offered:

Traverses. Those which are constructed to cover the flanks of the guns from an enfilade fire, are usually what are termed gabionades. To form a gabionade, gabions are placed in a row, side by side, enclosing a rectangular space of about twelve feet in width from out to out, and about twenty-four feet in length, perpendicularly to the epaulment.  A second row is placed within this and touching it.  The area thus enclosed is filled in with earth, to a level with the top of the gabions.  Four rows of large fascines are next laid on the gabions, to support a second tier consisting of one row. The second tier is filled in like the first, and the earth is heaped on top, making the gabionade nearly eight feet high. The work will be expedited by throwing up the greater part of the earth before placing the second tier.  Splinter proof traverses may be made by placing three thicknesses of gabions side by side filled with earth, with a second tier of two thicknesses on top.

Note here that Mahan described two classes of gabionades in this paragraph.  One was a shot proof and the other splinter proof.  The latter using about a third of the materials of the former.

Mahan offered this figure to illustrate a shot proof gabionade, as a type of traverse, in profile:

PlateVIFig38

As described, we see two sets of gabions on each side (four rows total on each side) on the lower tier.  Atop that fascines provide a platform for the second tier, which was two more sets of gabions (two rows on each side).  Those walls defined, the gabionade contained earth providing the mass protecting the gunners.  The result was a twelve foot wide structure (which would run twenty-four feet from the epaulment (or parapet, if you prefer) across the gun platform, which was atop the tread of the banquette. The traverse stood eight feet high, perhaps a little more.  These dimensions were governed by the height of the gun and required dimensions of the platform.  Recall platforms were supposed to run between fifteen and seventeen feet back of the parapet.

However, at the time Mahan was considering pre-war field and siege carriages.  During the war, large Parrotts and Columbiads required adjustments to the formula.  And we see that in the photos taken on Morris Island during the war:

03109a_Alt

No doubt here, this is Fort Putnam, built atop what was Battery Gregg on Cummings Point. We see a 10-inch Columbiad on the left and a Parrott (8-inch or 6.4-inch) on the right.  Based on the height of the ammunition crates and grape shot, this traverse appears to be twelve to fifteen feet tall.  The traverse is also much longer than specified by Mahan.  However, other photos in the same area demonstrate these traverses were also being used as magazines and shelters.  Thus the larger footprint was partly due to that functional arrangement.  We also see the surface is sod.  Based on engineers’ reports, these were built with gabions but surfaced with earth and sod to prevent the beach sand from blowing away.

An interior view of the works on Morris Island better illustrates the gabionades, or traverses, where not used in conjunction with shelters:

03113a

Here we see the breech end of a Parrott (looks to be a 6.4-inch) and the transom of its carriage standing out from behind the traverses.  Note the wood beams sticking out from the traverse on our left.  Such implies a stacking of tiers within, hidden behind that sodded surface.  A presumption here, but I’m pretty sure there were tiers of gabions within.  The Ordnance Manual gives the height of the trunnions on a 10-inch Columbiad wrought iron barbette carriage as 79 inches, or roughly 6.5 feet.  Add to that the height of the gun’s breech over the bore’s center line, and we’d have about 7.5 to 8 feet.  The top of the traverse is just above that breech band, so let’s call it eight to ten feet?  In the background a fellow is posing nicely on the side of anther traverse.  Looks to me he’s about four feet above the platform.  Add his height, and we have a second data point to consider. No rush, just go out and find out who the soldier is, consult his service records to obtain the height, and get back with me…. or let’s just call it as six feet more or less.  So a ten foot tall traverse?

I should also mention here the tactical setting for these traverses.  Readers know well those batteries were subject to counter-battery fire from Confederate guns on Sullivan’s Island and James Island.  And that fire was not some paltry 12-pdr or 3-inch projectiles, rather the largest and heaviest stuff available at the time.  We are talking about 7-inch Brookes, 10-inch Columbiads, and 10-inch mortars.  So stout traverses were certainly needed.

These photos provide a nice redirect to Wheeler’s description of such traverses in his 1882 instruction.  Expanding Mahan’s one paragraph, Wheeler offered over four and a half pages!  So we’ll look at that next week.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, pages 59-60.)

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