Writing the instructions for cadets, almost two decades after the Civil War, Junius B. Wheeler focused more on the functional requirements of outlets in the fortifications, as opposed to the important details of construction. The nuances here are, I think, important. Mahan presented the outlet had important operational uses within fortifications, but proceeded to discuss the particulars assuming the student would understand what those uses were. Wheeler focused on the uses up front, citing communications as the need and outlets as the remedy. And we must broaden “communications” a bit, perhaps our 21st century writers might say “traffic” and refer to movement of personnel, supplies, as well as messengers carrying communication.
Wheeler added to Mahan’s instructions with mention of “turn back” traverses at the mouth of outlets (to reduce the area under enemy lines of fire) and wider outlets for sorties. But for the most part, the construction techniques remained the same. Likewise, Wheeler identified the same supplemental structures as Mahan – barriers and bridges – while adding a few embellishments.
First off, we have the barriers. Which were… well… gates:
Barriers. – The outlets are usually arranged so that they can be quickly closed, to guard against surprise. The means used is a gate, technically termed a barrier.
The gate is made with two leaves, hanging on posts by hinges, and made to open inward.
The frame of each leaf is composed of two uprights, called stiles; two cross pieces, one at the other at the bottom, called rails; and a diagonal brace, called a swinging bar.
The leaf of the barrier may be open, by spiking stout upright pieces, with intervals between them, to the pieces of the frame; or it may be made solid, forming what is known as a bullet-proof gate.
Yes, something you might purchase, pre-fabricated, at the home improvement store. But note that Wheeler offered two versions – a light “open” leaf version with spaces between the uprights AND a heavy “bullet-proof” version with no spaces. The latter was illustrated in Figure 52 of Wheeler’s book:
Wheeler added some practical observations about the construction of these heavy gates:
Since the gate must be strong, the leaves of it are necessarily very heavy. The leaves must be hung upon stout posts, firmly braced into the ground, to sustain the great weight of the gate.
The top rails of all barriers should not be less than six feet above the ground.
In the barriers with open leaves, the vertical pieces are usually extended from eighteen inches to two feet above the top rails, and their upper ends sharpened.
In those which are solid, it is usual to arrange some obstruction upon the top rail, such as sharp pointed spikes, broken glass, etc., to interfere with persons climbing over the top. It is usual to provide apertures in the leaves, through which the men can fire upon the ground outside.
Gotta love those details. From having a “peephole” to shoot out from to having broken glass atop the gate.
Bridges were another supplement to the outlet’s composition:
Bridges. – When the ditch has been completed along that part of the work in front of the outlet, it is usual to carry the roadway across the ditch by means of a bridge.
The ditches of field works are, as a rule, quite narrow, and the bridges used to span them are very simple constructions.
A common method of building the bridge is to lay three or more sleepers across the ditch, and cover them with planks laid transversely. If the span is sufficient to require intermediate supports, these are obtained by using trestles placed in the ditch.
A bridge built in this way can be quickly removed and speedily re-built, if there be any necessity for it.
We might consider this a temporary bridge without any means for retracting or removing, save dismantling. Thus it was kept to the bare minimum arrangements.
Wheeler mentioned that other “hand-books on military engineering” described the use of draw bridges or rolling bridges in fortifications. He only briefly discussed the former, being basically as that detailed by Mahan in earlier texts. The latter were designed to be “… pushed out from the work, and drawn back into it.” Both sort of bridges were,
… known as movable bridges, are useful to guard against surprise, to prevent stragglers from entering, and to keep the garrison in the work. As a defense against an assault of a field work, they are of but little value.
To belabor that point:
The best method, is to have no ditch in front of an outlet, but let the roadway be on the natural surface of the ground.
Of course, operational needs might vary. But you get the point.
Wheeler offered one more supplemental structure under his heading of communications, but not one that was directly associated with outlets. This was the ramp. While all writers on fortifications discussed ramps in some regard, Wheeler saw fit to highlight the structure and its role for interior communications (and again, broaden that definition as mentioned above):
Ramps. – The short roads used in fortifications to ascend from one level to another, are termed ramps.
The width of a ramp depends upon its use, following the rule laid down for the width of passages. A width of six feet for infantry, and of ten feet for artillery, are the widths generally used.
The inclination of the ramp may be as great as one on six, and as little as one on fifteen, depending upon the difference of level between the top and bottom. The side slopes of earth with its natural slope.
The ramps in a work should be placed in positions where they will not be in the way, nor occupy room which may be required for other purposes.
Steps or stairways are sometimes used instead of ramps. The rule for them is that the breadth of each step, called the tread, shall be at least twelve inches, and the height of the step, known as the rise, shall be about eight inches.
They are substituted for ramps in those places where there is not sufficient room for the ramp.
Nothing new or advanced here. Ramps and stairs were part of fortifications dating back to the earliest times. What is noteworthy here is that Wheeler considered them part of the fort’s communication infrastructure… again communication in the sense of how one moves into, out of, and inside of the fort.
(Citations from Junius B. Wheeler, The Elements of Field Fortifications, New York: D. Van Nostrand, 1882, pages 151-5.)