Last week, we saw that prior to the Civil War, Mahan felt one paragraph of instruction was sufficient for cadets to understand how traverses might be used between gun platforms of the batteries. However, in 1882, Junius Wheeler, writing a textbook for cadets nearly two decades distant from the Civil War, felt the subject required much lengthier treatment. Mahan used the “fancy” word Gabionade and mentioned two types – shot proof and splinter proof. Wheeler dispensed with the label, simply calling these traverses, while holding there were still two basic forms:
Traverses. – The traverses constructed along a parapet are of two kinds, viz., the traverses built to afford shelter against slant and enfilading fires, and those built as a protection against fragments of bursting shells.
Wheeler’s definition discarded (as it was somewhat outdated by 1880) the notion of shot proofing. The main nemesis was the shell. Note also that Wheeler adds that traverses should protect against slat fires. So imagine an arc of about 30° off perpendicular that must be addressed.
Wheeler provided considerably more information for the cadets in regard to construction of these traverses:
Traverses may be built at the same time that the work is constructed, or they may not be built until there is an immediate necessity for them.
In the former case, their construction is in all things similar to that of the parapet, viz., tracing profiling and execution…
Thus the cadets were referred back to all that applied geometry involved with building the parapet and planning relief. Such is fine for those who plan for every eventuality. But who does that? Procrastination is always an option!
In the latter case, they are generally built in great haste, and profiles are not used. The construction is of the simplest kind, having for its object to interpose a mass of earth upon a line of fire, in the shortest time possible. This is done by piling sand-bags, filled with earth upon the spot to be occupied by the traverse, and then raising there a mass thick enough and high enough to server the end required. Gabions filled with earth are frequently used for the same purpose.
Swell! If you didn’t have the presence of mind to sort this all out before hand, and waited for the enemy to point out the flaws of your fortification, you should start by filling some sandbags. Lots of sandbags would be nice.
Wheeler continued on to relate the desired form of the traverse:
The top of the traverse is usually made ridge-shaped, so as to carry away the rain water which falls upon it. The sides of the traverse are sloped, the inclination of the slopes being the same, or different, according to the degree of exposure of the traverse to the enemy’s fire.
The traverse shown in Fig. 40 is an example of a traverse built to shelter the men on the banquette from a slant or enfilading fire, coming in the direction shown by the arrow. Its top is made ridge-shaped. The side toward the enemy has the natural slope of the earth; the opposite side is made steeper, and should be revetted.
Note also the traverse can be higher than the interior crest. Wheeler gave the engineer latitude to adjust according to the need – both for height and width.
The thickness of the traverse depends upon its exposure to the enemy’s fire. If a fire can be brought directly upon it, it should have the same thickness as that given to the parapet.
Its height and length depend upon the amount of banquette and terreplein which are to be defiladed by it.
The next structural question is how the traverse should link into the parapet, so as to avoid a mess or flaws. And Wheeler had an answer:
The manner in which this traverse is joined to the parapet is shown in Fig. 41, which presents its plan.
The slope on the side toward the enemy is shown, in both these figures, to be uniform. It is not always the case. The portion exposed to the enemy’s fire is given the natural slope of the earth; but below this plane of fire, the slope may be revetted, and made steeper.
Wheeler’s last remark about the form of these traverses allows for a modified profile:
Instead of being ridge-shaped, the traverses are, in many cases, made with a cross section similar to that of the parapet.
While an illustration would be nice here, I think we can imagine the suggested layout. Instead of a central crest on the traverse, the highest point would be on the side furthest from the enfilading fires. The top of the traverse would then slope down to the other top crest. Such would serve to both drain the top and deflect enemy fires.
So.. Wheeler spent the better part of three pages just describing the layout and construction of one type of traverse – something evolved from Mahan’s shot-proof traverse. Wheeler granted more latitude for the dimensions and put more emphasis on integrating the traverse into the overall fortification plan. Most important, Wheeler’s traverse were not just something to protect the guns in battery, but also to protect the soldiers manning the works.
Beyond this, Wheeler also gave splinter-proof traverses expanded coverage. We’ll look at that next week.
(Citations from Junius B. Wheeler, The Elements of Field Fortifications, New York: D. Van Nostrand, 1882, pages 128-30.)