Fortification Friday: Wheeler’s expanded instructions for traverses

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Wheeler’s definition discarded (as it was somewhat outdated by 1880) the notion of shot proofing.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.

WheelerFig40

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.

WheelerFig41

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.)

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.)

Fortification Friday: Interior Arrangements, starting with armaments

The next aspect of field fortifications to consider are the interior arrangements.  Thus far most of our focus has been towards the exterior, with the exception of the traverses, and what could be done to block or stop the attacker.  With the interior arrangements, the engineer would consider what could make the defenders’ job easier and, shall we say, more comfortable.  Mahan prefaced his lesson on interior arrangements by calling attention to such factors:

Under the [heading] of interior arrangements is comprised all the means resorted to within the work to procure an efficient defense; to preserve the troops and the material from the destructive effects of the enemy’s fire; and to prevent a surprise.

You are probably thinking, “protect the troops?  Isn’t that what the parapet does?  Doesn’t the ditch prevent surprise?”  Well… yes… you might look at it from that standpoint.  But what Mahan was calling attention to here were the structures and features which were internal to the works and designed to improve the nature of the defense.  As such “within the work” is the important phrase to consider.  But, keep your questions in mind as we work through this topic, as we will revisit shortly.

Mahan continued to offer a list of classes of these interior arrangements:

The class of constructions required for the above purposes, are batteries; powder magazines; traverses; shelters; enclosures for gorges and outlets; interior safety-redoubt, or keep; and bridges of communication.

From that we have a subdivision:

All arrangements made for the defense, with musketry and artillery, belong to what is termed the armament.

So we have a name for structures to support things that shoot.  Armaments.  Just for the context of these field fortification discussions, OK?

The armament with musketry is complete when the banquette and the interior and superior slopes are properly arranged, to enable the soldier to deliver his fire with effect; and to mount on the parapet to meet the enemy with the bayonet.  For this last purpose stout pickets may be driven into the interior slope, about midway from the bottom and three feet apart. The armament with artillery is, in a like manner, complete, when suitable means are taken to allow the guns to fire over the parapet, or through openings made in it; and when all the required accessories are provided for the service of the guns.

So… yes the parapet’s design can be considered part of the interior arrangements.

Mahan continues with this profound statement:

The armament with artillery is a subject of great importance….

You got me at “great importance.”

Oh, wait, I cut the professor off.  He has more on this ….

The armament with artillery is a subject of great importance, because it is not equally adapted to all classes of works.  Experience has demonstrated that the most efficient way of employing artillery, is in protecting the collateral salients by a well directed flank and cross fire, which shall not leave untouched a single foot of ground within its range, over which the enemy must approach.  It has moreover shown, that a work with a weak profile affords but little security to artillery within it; for artillery cannot defend itself, and such a work can be too easily carried by assault to offer any hope of keeping the enemy at a distance long enough to allow the artillery to produce its full effect.

The logic here is “form should follow function.”  If the intent is to have artillery fire on the enemy in order to break up the attack, then a flank fire is recommended.  And that artillery should blanket the approaches with fire… “shall not leave untouched a single foot….”  Artillery sits at the top of the list when making decisions about weapon placement.  It is the most effective, man per man, weapon for influencing the battlefield Not necessarily saying “killing” or producing causalities, but influencing the other side’s actions.  Yet, artillery’s influence is best gained over longer ranges.  Thus the need to form works that not only provide the artillery a measure of protection but also keep the enemy at greater than small arms length (range).

The best position for artillery is on the flanks and salients of a work; because from these points the salients are best protected, and the approaches best swept; and the guns should be collected at these points in batteries of several pieces; for experience has likewise shown, that it is only by opening a heavy, well-sustained fire on the enemy’s columns, that an efficient check can be [given] to them.  If only a few files are taken off, or the shot passes over the men, it rather inspires the enemy with confidence in his safety, and with contempt for the defenses.

Sun Tzu should have said it!  Don’t let the enemy become contemptuous of your defenses!

Consider the “best practice” offered by Mahan.  By placing artillery on the salients, the guns were out of the direct line of the attacker’s fires while being placed behind the various, and likely complex, defensive works on the “horns” of the bastion.  And artillery shouldn’t be parceled out as singles, but rather massed and inter-operated to multiply the effect.

All this is great theoretical talk.  Everyone would agree massing artillery is best.  But now we have a practical problem on the parapet.  With infantry, the parapet works fine to protect most of the body, provide cover to crouch behind when reloading, and, if the fight is close, an orientation for the bayonets.  But artillerymen cannot “crouch” an artillery piece.  And when servicing the weapon, they are exposed. Furthermore, there are all sorts of problems bringing 12 pound or 24 pound or larger projectiles up to the gun.  So to make the big guns work best, one must make arrangements.. in the interior…. And those arrangements Mahan identified under the classification of “batteries.” We’ll look at those next.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, pages 51-2.)

Fortification Friday: Attention to the all important traverse!

Thus far as we’ve examined, in meticulous detail, how to address relief in the planning of a field fortification, we’ve focused on the parapets.  Getting those tailored would protect against direct fire against the defenders of a particular face – direct defilement as we call it.  Mentioned earlier, the works also needed reverse defilement to protect the backs of those defenders.  That was the job of the traverse.

Let us pause for the moment to explain the traverse. The traverse was an internal structure within a work which was designed to intercept enemy fires or reduce the impact of an explosion.  Traverses filled a number of vital functions within the works and there were a number of variations, based on those functions.  We see traverses along a line, designed to intercept flanking fire.  Traverses might form a secondary facing along a line.  We also see traverses as sort of a “backstop” behind a sallyport.  And also traverses situated around magazines could prevent a disaster caused by a lucky shot (or stray ember).  But here we are looking at traverses built within a salient and intended to block enemy fire from the rear of the face. Such are defilade traverses (though I would point out defilade traverses apply here to both reverse and enfilade defense).

Going back to our notional figures, thus far Mahan had instructed how to determine the height of the parapet.

PlateIIFig16C

That accomplished….

To determine the height of the traverse is the next step.  To do this, the height of the tread of the banquette is ascertained on the three poles, B,C,D, and a distance of nine inches is set off on each pole above the tread.  Between the points thus determined a cord is stretched, or if the distance be too great for this, two pickets may be placed between B and C, and a cord, or straight edge, be fastened to them in the required direction.

Please note the mark set off on these well used poles.  This mark is but nine inches above the banquette – that being the location where the defender stands to shoot over the parapet.  The intent is to build a defense which will prevent the enemy from firing on that piece of ground from the rear.

An observer is then placed at the pole F, and another places himself behind the line B C, so as to bring the cord, and the points O’ and F, in the field of vision; he then shifts the position of the eye until the cord is brought to touch the point O’; he then directs the observer at F to mark the point on the pole where it is intersected by the plane of vision.

This is somewhat confusing at first read, but remember that at this time in the construction of the works, the parapets and other structures were not yet built. So the observers are walking over what is relatively level space. Still, this is difficult to depict on the diagram without the risk of confusion to the reader…

PlateIIFig16D

Work with me here – we have the line marked off between A-B-C.  The second observer is somewhere there behind that line (and outside what would be come the works later on).  Then the second observer directs the positioning of our original line of F-C until that cord, along with cord A-B-C and the line to O’ all sit in the same plane.  That would determine the “mark” used as the baseline for the traverse. (I know what you are thinking… nine inches?  Hold on to that for a second.)

Mahan continued:

A similar operation is performed with the point O, and the face C D, and above the highest point thus determined on F, a distance of five feet is set off for the top of the traverse at F; and five feet nine inches is set off above the tread of the banquette at C for the top of the traverse at that point.

So, pick the highest of the two baseline marks, add five feet to cover the backs of the standing musket-firing infantryman, and you have the desired height the traverse. Oh, and with that we have a new term to use:

The planes which determine the top of the traverse, are termed planes of reverse defilement.

That’s good because, as you probably have figured out, fortifications are built upon a firm foundations of technical terminology.  The more buzzwords the engineer offered, the better the fort.

The height established, there were other details needed to finalize the traverse:

The traverse is finished on top like the roof of a house, with a slight pitch; its thickness at top should seldom exceed ten feet, and will be regulated by the means the enemy can bring to the attack; its sides are made with the natural slope of the earth; but, when the height of the traverse is considerable, the base of the side slopes would occupy a large portion of the interior space; to remedy this, in some measure, the portion of the sides which are below the planes of direct defilement, may be made steeper than the natural slope; the earth being retained by a facing of sods, &c.

I would offer that the “etc.” mentioned here included gabions.

OK, that’s the height of the traverse… what about the length needed?

When the salient of the work is arranged for defense, the traverse cannot be extended to the salient angle; it is usual to change its direction within some yards of the salient, and unite it with the face most exposed.

Keep in mind the traverse outlined above was designed to counter reverse fire on a face.  We mentioned traverses also worked to stop enfilading fire.  So more traverses were needed in the works:

Traverses are also used to cover the faces exposed to an enfilade fire; for this purpose they are placed perpendicular to the face to be covered. If several are required, they may be placed twenty or thirty yards apart; each traverse should be about twenty-four feet long, and thick enough to be cannon proof.

With all that figuring in place, the engineer could start pointing out were the shovels should go to work.

Keep in mind this process applied to the open works (with the open gorge).  The same could be used for enclosed works, with a few other considerations.  Next week, we’ll look at those along with some other “tips” offered by Mahan.

(Citation from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, page 28-30.)