Fortification Friday: Let’s put some platforms beneath the cannons!

In the most recent installments of Fortification Friday, we’ve looked at the ways to mount artillery in the fortification, according to Mahan’s instructions.  These methods involved barbette batteries, firing over the parapet, and embrasures, allowing the guns to fire through the parapet.  One more detail need be discussed in regard to placement of the guns – the actual surface on to which the guns sat.  We’ve touched upon this to an extent by identifying the mound used for barbettes (and sometimes for embrasures where the parapet is tall).  And we’ve defined the area required to allow for recoil of the gun.  But we have not taken into account the effects of that recoil on the mound or earth where the gun is placed.  In order to prevent damage to the fortification, the area detailed for the gun needed strengthening.

And that strengthening was called a platform.  So let us pick up with Mahan:

Platforms.  When a gun is fired often in the same direction, the ground under the wheels is soon warn into ruts; it is to prevent this, that platforms of timber are used in such cases.

Sometimes I will slip-up and refer to the mound of the barbette as the platform, as it does somewhat function as a platform under Webster’s definition.  But strictly speaking, if we are talking forts, then we work with Mahan’s definition. And Mahan said specifically that platforms are the timber support placed under the gun’s firing position.

From that, Mahan explained the preferred arrangement of the platform:

The shape of the platform is usually a rectangle; in some cases, where a wide field of fire is to be obtained, the form is a trapezoid. The rectangular platform is ten feet wide, and seventeen feet long, for siege pieces; and nine feet wide and fifteen feet long, for field guns.  It consists of three sleepers of six inch scantling, either fiften or seventeen feet long, which are laid perpendicular to the direction of the epaulment, and are covered with two-inch plank, twelve inches wide, and cut into lengths of nine or ten feet.  Between the ends of the sleepers, and the foot of the genouillére, a piece of eight-inch scantling, nine feet long, termed a heurter, is laid; it should project about six inches above the platform, and be bisected by the directrix.  The object of the heurter is to prevent the wheels from being run against the revetment, and also to give the gun its proper direction, particularly in night firing.

So let’s turn to the figures to illustrate how this looked:

PlateIVFig33bisPlatformA

This is a sub-section of Figure 33 bis, which we used when discussing the construction of embrasures.    We are provided a view from above (on the right) and another from the side (to the left).  This platform is for an oblique embrasure, and thus oriented based on a directrix angled to the right-front of the parapet.  Breaking this down by parts:

PlateIVFig33bisPlatformB

I’ve outlined the three sleepers in red – six inch square timbers, fifteen to seventeen feet long.  Just one of the planks is outlined (in gold color), for simplicity.  Those were two inch thick, twelve inch wide, and nine to ten feet long.  Lastly there is the heurter in green – eight inch square and nine feet long.  Note how the heurter is not as wide as the planks.

The dimensions of the platform were larger than the actual footprint of the gun itself so as to allow the crew better footing, and to be at the same level as the gun they were servicing.

Notice the position of the heurter in the diagram.  As Mahan stated, this position prevented the gun from rolling forward into the works.  And it also gave the crew a fixture to “square” the gun when placed into battery for firing.  Off that, the gun might be oriented off the directrix to suit the necessary traverse, and elevation, as needed.  I’ve seen mention of stakes or other marks used by the crews to facilitate rapid orientation of the gun on certain targets. Say like having a mark on the platform indicating the orientation (and perhaps even the elevation) to aim at a ditch just off the directrix.  Old school “registration” of fires, if you wish.

Mahan continued with instructions for building the platform:

To lay a platform, the earth on which it is to rest should be well rammed and leveled; three trenches are then made for the sleepers, two of which should be placed under the wheels, and the middle one under the trail.  The sleepers are laid flush with the ground, and firmly secured by pickets driven at their sides and ends, and the earth is solidly packed in the trench around them; the plank is then laid and secured by nails, or some other fastenings.

Notice the sleepers are placed in trenches and actually lay close to, if not at, ground level.  This ensured the planks were not raised significantly above ground, and thus would not become a hazard during action.  Nothing more embarrassing than having the powder monkey trip over an exposed plank or sleeper!

And should the platform be level all around?

If the platform is for direct firing, with full charges, the tail may be six inches higher than the front to break the recoil; in all other chases it should be horizontal.

So for certain arrangements, a nice slope to arrest the recoil of the gun was specified.

Mahan also offered a plan for simplifying the platform if necessary:

A platform may be constructed simply of three pieces of timber, one under each wheel, and one under the trail, firmly secured by pickets, and connected by cross pieces, into which they are halved.

Illustrated as such:

PlateIVFig32E

Such was probably best used for embrasures with very limited range of traverse.  With a wide traverse, more surface area would be needed.

Of course, that brings up question about arranging for barbettes where a wide traverse was desired:

For barbettes, the platform may be dispensed with; or, if used, the whole surface nearly of the barbette should be covered.

So if you didn’t want to waste the timber, the barbettes wouldn’t need one.  From wartime photos, we see barbettes with and without platforms.  And where used with a barbette, a trapezoidal, verses the square, platoform was more likely:

If the platform is made of a trapezoidal form, it will require five sleepers.

No illustration of this was offered.  But likely these sleepers were angled off the outside pair, to provide support for planks running further out at the rear of the platform.  And there was no set layout for placing planks across those sleepers.  Thus we are left to assume some common sense and practical experience dictated the arrangement from there.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, pages 56-8.)

 

 

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