Mahan on Artillery Tactics, Part 2: The “Place” of Artillery

Let us continue focused on this discussion of Dennis H. Mahan’s thoughts of artillery tactics, in the pre-Civil War context. In the previous post, we noted some of the context to the label of “tactics” in the Civil War-era manuals. But the key point was what Mahan called the duties of artillery – “… to support and cover the other arms; keep the enemy from approaching too near; hold him in check when he advances; and prevent him from debouching at particular points. ”

I offer a 21st Century sound-byte worthy summary of this as – to deny the enemy commander a course of action. And correspondingly, that would grant the friendly commander a different set of options. That’s my interpretation. So feel free to disagree, and drop a comment. To me, Mahan’s duties boil down to the use of artillery in a way that prevents the enemy from using particular pieces of terrain (in defense), opting to attack by way of a particular approach (in offense), or at least keeping the enemy at greater than musket range. Perhaps another way of putting it – forcing the enemy commander to adopt something other than the simple, apparent plan of action. (And with a complex plan adopted… the enemy commander leaves himself open to all sorts of criticism from later day historians who shall question his ability!)

Mahan continues on, later in his opening chapter, to describe the place of artillery on the battlefield, in his estimation. Initially he described the metaphorical place on the battlefield:

The artillery, which had for a long period, and even still, preserves the character of eminent respectability, has of late years begun to infuse a dash of the dare-devil spirit of the cavalier into its ranks. If it has not yet taken to charging literally, it has, on some recent occasions in our service, shown a well-considered recklessness of obstacles and dangers, fully borne out by justly deserved success.

Some will read this passage and begin shouting about the artillery charge and such. Not even close! Rather what Mahan is suggesting is that artillerymen of his time (the 1840s) were inclined to more aggressive placement on the battlefield, not simply running up within musket range to trade blows with the infantry. So what was that aggressive placement?

Well to start with, Mahan points out that artillery conformed to classifications – heavy and light (with divisions for foot and horse artillery) – each of which had places tailored to their strengths and weaknesses. Heavy artillery, which he categorized as 12-pdr caliber and above, was reserved for batteries of position and “is seldom shifted during the action” Light artillery, being 6-pdr gun and 24-pdr howitzers (!), included foot artillery and horse artillery. Foot artillery being those batteries with the standard allocation of horses, and which the crews marched alongside (usually). Horse artillery, of course, received sufficient animals to allow the crews to ride, and were thus more quickly moved on the field. Both were to “follow the movements of the other arms.”

However, as we well know, those classifications were soon blurred by technological advances – notably “light” 12-pdr guns and rifled artillery. And such brings to mind the “chicken or the egg” debate as to the technological advances driving tactical innovations, or vice-versa. I think Mahan argued “both”:

Improvements both in the materiel and the tactics of artillery have been very marked within late years. Formerly, considered only in the light of an auxiliary on the battle-field, artillery now aspires, and with indisputable claims, to the rank of a principal arm. Its decisive effects, at the late battles on the Rio-Grande, are supported by testimony too emphatic to be overlooked.

Worth noting, in this passage, Mahan left a footnote, not to Captain Samuel Ringgold as one might guess, but rather to Joel R. Poinsett. He gave the former, and late, Secretary of War credit for reforming the US Army and ensuring the the force was ready for the test of combat… and we have discussed his artillery reforms on occasion.

Mahan continued on, lauding the artillerists of his day:

From the studies required of him, the artillerist is well trained to maintained the characteristics of his arm; courage of the highest order, in which the physical is always under the control of the moral element, producing, as necessary result, unbounded devotion to the task assigned; a presence of mind that nothing can disturb; and that coolness which no danger, however appalling, can impair.

Ladies and gentlemen! I give you Marvel’s new super hero! Artilleryman! If nothing else, a description that we should all aspire to.

Turning back to serious matters, we have that question about “place” … not in the metaphorical sense… but as in WHERE to put the cannons. And Mahan got around to that:

The tactical applications of artillery on the field depend on the caliber. To the heavy are assigned the duties of occupying positions for strengthening the weak points of the field of battle; for securing the retreat of the army; for defending all objects whose possession might be of importance to the enemy, as villages, defiles, &c.; and for overturning all passive obstacles that cover the enemy, or arrest the progress of the other arms.

Although the distinction of “heavy” artillery would drop just over a decade after Mahan wrote this passage, the guidance remained valid. More to the point, we see examples of how the artillery might be placed to, as I put it, take away options from the enemy. In particular turning weak points into strong ones, retaining possession of key terrain, and countering passive obstacles.

As for the light artillery:

The light pieces, served by foot-artillery, follow the movements of the infantry; covering the flanks of its position, preparing the way for its onset, and arresting that of the enemy. It is of this that the principal part of the artillery in reserve is composed.

Employed directly to support the infantry, artillery prevented the enemy from arresting (not stopping… words have meaning) the friendly advance. Likewise on defense, the artillery arrested the enemy advance. In both cases, that translates to taking away options open to the enemy commander. Perhaps others will expand that role to MAKING options for the friendly commander… which would also be a good way to put it.

The horse-artillery is held in hand for decisive moments. When launched forth, its arrival and execution should be unexpected and instantaneous. Ready to repair all disasters and partial reverses, it, at one moment, temporarily replaces a battery of foot, and at the next is on another point of the field, to force back an enemy’s column. In preparing the attacks of cavalry, this arm is often indispensable and always invaluable; brought with rapidity in front of a line, or opposite to squares of infantry, within the range of canister, its well-directed fire, in a few discharges, opens a gap, or so shakes the entire mass, that the cavalier finds but a feeble obstacle, where, without this aid, he would in vain have exhausted all his powers.

Three “places” for horse artillery offered as examples: rushed to replace a pressed battery of foot; dispatched to break an enemy assault; or used to prepare the situation for a cavalry charge. In that latter role, the artillery moved forward within canister range… that’s C-A-N-I-S-T-E-R… not grape-shot. And that is considered between 200 and 400 yards. Musket range, before the wide adoption of rifles and mine-balls, was still considered at 100 yards. Arguably, even after technology allowed for more range, the infantry tactics still governed engagements with the musket at 100 yards.

Note that not once does Mahan suggest the artillery should, themselves, charge forward. None of these alleged artillery charges. It simply was not part of the doctrine which he described here. Artillery was not supposed to BE the attacker. Artillery was supposed to make the way easier for the attacker.

Another take-away from this passage is the alignment of the horse artillery. As Henry Hunt would argue during the war, the horse artillery was not simply assigned to support the cavalry. Rather the horse artillery should be a general reserve, used where the situation warrants. If that be supporting the cavalry in its mission, then so be it. But the horse artillery also had a role outside of that. And often that was far more important than simply aiding the defense of distant picket posts.

If nothing else, these passages, across but three pages in the manual, refute many preconceptions about how artillery was to be employed. The guns were not to be wasted simply standing in an augmentation of the infantry line, belching canister. Such would simply be employing the guns with their casualty-creation ability in mind. Instead the artillery was there to influence the battlefield situation, with focus on the cannon’s ability to exert control over a greater distance than capable with the other arms. In such way, we see the value of the artillery – its value as a combat force multiplier – in exponential terms.


(Citations from Dennis Hart Mahan, An Elementary Treatise on Advanced-guard, Out-post, and Detachment Service of Troops, and the Manner of Posting and Handling Them in Presence of an Enemy, New York: John Wiley, 1861, pages 45-7.)

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Artillery on the Battlefield: Tactics according to Mahan

Looking back at last year, one highlight of, as the disciples of social media say, the “content offering” from this blog was the Artillery tour of First Manassas, held jointly with Harry Smeltzer of Bull Runnings fame. The objective was to analyze the artillery employment at First Manassas with an eye to what we call, in the modern terminology, the tactical doctrine. Not to say things like “I could have done it better” or even “this is where he/they screwed up.” But rather specifically to ask if the employment was “by doctrine” – as in what a commander was expected to do – or was there some innovation going on, either intentional or unintentional. The preface to that “on the field” discussion was a series of quotes from pre-war writings, mostly in manuals that the officers of the time would be exposed, about the use of artillery on the battlefield.

First off, when discussing Civil War tactics, we have to pause and recognize things called “tactics” then were not necessarily what we call tactics today. As such our discussion has to incorporate some translation. For instance, a book titled “Field Artillery Tactics” from 1861 tends to be more so a manual detailing drill of artillery (from the artilleryman up to the battery level). That sort of thing is important, as the complex choreography involved with moving and servicing a gun must be part of the context. But when addressing the question posed above, in relation to the placement and employment of the artillery, we are left wanting descriptions about how a commander should use the artillerymen and their wonderful cannon.

For modern times… pretty much anything since the dawn of the 20th century, I could point you to a series of Army manuals that take us through the entire spectrum – technical manuals, drill manuals, and tactics manuals, all labeled as such. More to the point, I could reference manuals for tactics at the squad, platoon, company, battalion, regiment/brigade, and division level… or for artillery, by gun, section, battery, and battalion. But for the Civil War, we lack such granular detail. I don’t take that so much as a knock on the discipline of military science as practiced at that time, but more so a shortcoming due to a lot of presumptions. The foremost of those presumptions was that a young officer would receive all the tactical training needed at his first duty station. More so, an officer would be “indoctrinated” to the nuances of handling a cannon, a section, or a battery under fire; and further along become aware of the manner in which those guns should be employed. That’s a peacetime luxury, of course. Rapidly expanding armies and the pace of the war outstripped such an indoctrination system.

Still, there should be, and was, a starting point for those discussions. And I submit if we are going to point to one manual that was the American starting point, that was Dennis Hart Mahan’s An Elementary Treatise on Advanced-Guard, Out-Post and Detached Service of Troops, and the Manner of Posting and Handling Them in Presence of an Enemy, with a Historical Sketch of the Rise and Progress of Tactics, &c., &c., Intended as a supplement to the System of Tactics Adopted for the Military Service of the United States, and Especially for the Use of the Officers of Militia and Volunteers. (Yes, I like to introduce that title when playing charades.) Or as many simply refer to – Mahan’s Outpost.

Right off the bat, we see from the full title that Mahan intended his manual to further the discussion based on the established system of drill, called tactics. And considering the original publication date, in 1847, this “system” was that defined by General Winfield Scott. Those were, arguably, tested by fire and deemed sound. But those focused, as alluded to above, on how to move infantry, cavalry, and artillery. Not much in that system as to the “why” one would want to select a particular movement over another… in other words, what we today perceive as tactics. The problem was that officers in the lower echelons were often never exposed to the theories and practices beyond drill. And in the American experience, where grand armies had rarely taken to the field, it was those same junior officers often entrusted with vital operations.

Mahan hit upon that gap in the preface to his treatise:

The suggestion of this little compilation originated in a professional intercourse, some months back, with a few intelligent officers of the Volunteer Corps of the city of New York.

The want of a work of this kind has long been felt among our officers of Militia generally, as the English military literature is quite barren in systematic works on most branches of the military art, especially so on the one known among the military writers of the Continent as La Petite Guerre, or the manner of conducting the operations of small independent bodies of troops….

Wouldn’t you have wanted to be a fly on the wall during that discussion in New York?

Mahan opened his manual with a chapter covering the historical evolution of military science. Then started chapter two with the definition of “tactics”:

Tactics may be defined to be the art of drawing up, and moving troops systematically. It admits of a classification into two divisions. 1. Minor or elementary tactics; under which head may be placed all that refers to the drill, and other preparatory instruction of troops, to give them expertness in the use of their weapons, and facility of movement. 2. Grand tactics; or the art of combining, disposing, and handling troops on the field of battle.

This explains, somewhat, that translation I mentioned above. What we’d call “drill” today, Mahan considered minor or elementary tactics. And it is those “grand tactics” which we want to consider here. Most specifically, how did the artillery factor into those grand tactics. What, according to Mahan, was the artillery supposed to do on the battlefield? Well we turn to page 39:

The artillery is placed third in rank among the arms. Its duties are to support and cover the other arms; keep the enemy from approaching too near; hold him in check when he advances; and prevent him from debouching at particular points.

There, in one lengthy sentence, is the role of artillery on the Mahanian battlefield. Mahan’s vision of this is not just some passage in a book. This was part of the curriculum taught to his students, and his student’s students. Indeed, the majority of Civil War generals had benefit of Mahan’s teaching, either directly or indirectly. So this is an important passage when considering how artillery was used or mis-used on a Civil War battlefield.

Looking at this deeper, consider the nuances here. In the Mahanian context, the infantry and cavalry have the first and second rank, respectively. Their roles are tied to objectives, be that a piece of territory or imposition of a situation. But we mostly think of them as seizing and holding terrain. We might add to that the cavalry’s capacity for gathering information (actively or passively, as in scouting or picketing, respectively). But in the grand sense, the infantry could do the same, but as in all things just slower than the cavalry.

But artillery’s role was not tied to those higher order objectives. Rather to support the infantry and cavalry in attaining those objectives. But how is that done? By effecting enemy actions and activities – keep that enemy at a distance; stop or at least weaken an enemy attack; and deny the enemy use of good terrain. I like to put it this way – and this is my translation of Mahan for our modern ears: The role of artillery is to deny the enemy commander a course of action.

Deny a course of action? Yes. Roll that around for a bit. Try this exercise for any artillery position you’ve considered on a Civil War battlefield – From that point, what influence did they have on the battle? In every case, that will devolve down to the artillery either preventing or not preventing an enemy from executing a course of action. Maybe that course of action was to move up a particular route to attack. Maybe that course of action was to form a defensive line. Or maybe the artillery simply prevented, just by being there, the enemy from selecting a road other path for use in battlefield movement. But either way, the success of the artillery at that position was measured in the impact it had on the enemy commanders’ actions, specifically the courses of action available. Or if you prefer, the enemy commander’s options.

I would submit that if that be a positive influence (for the “home” side of that artillery) then the guns were well placed, and Mahan would have been happy. Were that be a negative influence on the battle, particularly where the guns became the “objective” instead of being the support for the other arms, then Mahan would have contended his lessons went unheeded.

Fortification Friday: Mahan’s American Blockhouse

One of the themes I’ve worked in this series of posts is a comparison between pre-war and post-war manuals. In small ways, the comparison points to the influence of wartime experience in the practice of military science… at least in the American army.  Another such example is the use of blockhouses.  Pre-war, Mahan discussed blockhouses in relation to field fortifications as a safety redoubt or keep.  That was not, of course, to say such was the exclusive use of blockhouses.  But Mahan simply offered less thought about the use of stand-alone blockhouses. Rather the emphasis was upon structures which would be used in conjunction with standard, conventional field fortifications to meet the traditional needs of an army on campaign. Again, this is not to say Mahan didn’t agree with stand alone blockhouses, but rather that in instructions to his students he put all the emphasis on blockhouses used as keeps within field fortifications.  So this is a “how they were taught” consideration instead of a “this is the only way they would use it” declaration. Keep that fine point in mind.

On the other hand, the American military experience, drawn out even more so by the Civil War, included the need for fortifications guarding rear areas.  In particular, protection of railroad lines, bridges, and other such infrastructure was rather important. And, as we know from ample examples from official records, photographs, and other sources, the blockhouse became the preferred fortification for that need.  And Mahan identified that in his post-war writings, declaring an American-ism in such employment:

American Block-House. In the more recent block-houses erected in our service for the protection of bridges, railroad stations, etc, the sides and roof … are constructed with a double thickness of logs eighteen inches in diameter, hewn to a face of eight inches where they are in contact.  The inner logs are placed upright, the outward horizontal. A space is left in the outward casing sufficient for the fire from the loop-holes made through the inner. The horizontal logs above the loop-holes are held up by short uprights, mortised into them and into those just below. The ceiling is covered with earth, as shown in the section, three feet thick at the ridge and sloping towards the eaves to about six or nine inches, where it is confined by a pole plate. The earth is protected from the weather by a board roofing.  Tin or sheet iron ventilators are made through the roofing and ceiling, and a brick flue to receive the pipe of the stove used in cold weather.

The loop-holes are nearly of the same form and dimensions of those already given.

Mahan gave us two sets of illustrations supporting this passage.  The first demonstrated the blockhouse particulars mentioned above:

MahanFig48_49_50

We see a double layer of timbers – the inner most placed vertical and the outer laid horizontally. In both cases, the logs are flattened on the sides in contact to close up any gaps.

Also notice the provisions for loopholes.  The dimensions remained the same, generally. But instead of simply carving out loopholes, Mahan suggested a more elaborate arrangement.  I’d describe this as a set of small columns between a gap in the outer, horizontal timbers.  Traditional loophole cuts are made in the vertical timbers of the interior. So there is still the double row of protection and the minimum opening required for the musket barrel.

I say a picture is worth a thousand words:

02147r

This is a blockhouse protecting the railroad between Nashville and Chattanooga in Tennessee.

Continuing, Mahan offered more elaborate plans for these blockhouses:

Some of these structures are built in the form of a cross, consisting of a square central chamber, twenty-four feet on a side, and of four wings of the same form and dimensions when the block-house is for cannon. An embrasure is pierced in each of the three sides of each wing to serve a single gun.  The cheeks of the embrasures are faced with logs, and the mouth is secured by a musket-proof shutter with a loop-hole in it.  The embrasures are below the level of the loop-hole, allowing these to be used whenever necessary.

Though not exclusively for the employment of artillery, the implication is that guns required more space within the fort and thus more elaborate arrangements were needed.  The addition of shutters is noteworthy and speaks to the need for crew protection in the era of muzzle-loading artillery.

But where you have artillery, you must also have a magazine:

Arrangements for magazines and store-rooms are made under the floor of the block-house in the most secure parts.

Ah… OK… answers that question.

And what about the entrance:

The entrance to the block-house may be either through a postern, the bottom of which is on the level of that of the ditch, a ramp leading from this level outwards, a door properly secured, and steps, forming the inner communications; or it may be arranged as shown in Fig. 51, 52, with a plank thrown across the ditch on the same level as the natural ground, the entrance to the door being masked by a double stoccade, leaving the same passage-way as that of the doorway.  Loop-holes in the door and sides of the building sweep this passage.

And here’s the referenced figures:

MahanFig51_52

Also note in this set of figures, and that above, the berm built up against the blockhouse.  As discussed earlier, this improved the defensive quality of the work, particularly against artillery.  Furthermore it prevented the enemy from hiding under the loopholes.  We don’t see that in the wartime photo above.  I’m of a mind we are seeing a blockhouse in the final stages of construction, rather than some flaw in the engineer’s design.  Other wartime photos show earth banked up against the blockhouse:

02151r

This is another Tennessee blockhouse.  Wonderful details to consider – the loopholes and the entrance stand out nicely.  And consider the figure offered by Mahan (post-war) to illustrate the two story blockhouse:

MahanPage65Fig1_2

Can you find a better match? That’s great stuff!

Another illustration Mahan provided in the post-war manual detailed arrangements for the loopholes.  So while he “said” such was “already given,” teaching after the war he saw need to elaborate.  We’ll look at that next.

(Citation from Mahan, An Elementary Course of Military Engineering: Part 1: Field Fortifications, Military Mining, and Siege Operations, New York: John Wiley & Son, 1870, page 62-3.)

Fortification Friday: Loopholes and Vents for the blockhouse

Last week, we discussed the layout and arrangements for the blockhouse, when used as part of a keep in the interior of a fortification.  An important requirement, if the keep was to function as intended, was the ability of the defenders to fire out of the blockhouse.  Just as with building the banquette, embrasures, and other arrangements on the parapet, such arrangements within the blockhouse necessitated attention to details. And those details come in the form of loopholes and vents, as Mahan would write:

The loop-holes are three feet apart; their interior dimensions are twelve inches in height; and eight inches in width for sides twelve inches thick; and twelve inches square for sides two feet thick. The width on the exterior, for the same thicknesses, will be two-and-a-half and four inches.  The height of the loop-hole on the exterior will depend on the points being defended; it should admit of the musket being fired under an elevation and depression. The height of the loop-hole above the exterior ground is six feet.

The visual you should have in mind is that of an aperture which is small on the exterior but larger for the interior.  This would allow the defender to train the musket across a wide arc, as well as providing for elevation and declination.  I don’t like mixing field fortifications with permanent fortifications, but in this case the application is along the same lines.  So consider the loop-holes here at Fort Pulaski, to the right of an embrasure:

Ft Pulaski 3 Aug 11 1346

In this case, there was need for the muskets to cover two zones.  So we see two loopholes incorporated as a pair.  Note the placement of stone slab above and below to strengthen the loophole structurally. Something not needed within the wooden blockhouse – simple cut outs within the timbers usually sufficed.

But the major difference between the blockhouse and brick fortification’s loopholes is the height.  Mahan specified only twelve inches for the blockhouse in a field fortification.  Those at Fort Pulaski are two feet or so.

Another aspect to keep in mind is the depth of the wall.  As the wall became thicker, the loophole’s lateral dimensions, particularly interior, increased.  Geometry at play here, as the musket would need more clearance on the interior as depth increased.

Mahan did not directly discuss interior arrangements for the artillery’s embrasures.  Partly, I think, as such an allocation would have pulled valuable cannons off the fort’s primary defensive line to that of the secondary or even tertiary defenses. But, we can deduce such arrangements would match those described for embrasures through the parapet.  In short, a larger loophole… which is what we see to the left of the photo above.

All this is good thinking.  But we also have to keep in mind the by-product of firing any weapon.  In order to push the projectile out of the barrel, firing of the powder creates gasses. That foul air is not an issue out in the open or on the parapet.  But in the enclosed space of the blockhouse, there is need to expel the gasses:

Vents for the escape of the smoke are made over each loop-hole, between the cap-sill and the top pieces.

Moving to another location in Fort Pulaski, we see a vent above one of the other embrasures:

Ft Pulaski 3 Aug 11 1388

See the weathering on the paint?

Mahan does not provide much information on constructing vents for the blockhouse. These could be vents between the ceiling and wall. Or vents incorporated in the wall itself.  To maintain integrity of the structure, in terms of defense, those vents were best created using an interior angle.  That would allow gasses to vent.  But water… or things the enemy might want to push inside… would be restricted.

From there, Mahan gave brief descriptions of the camp bed (which we noted served as the banquette inside the blockhouse), racks, and other storage arrangements.  But with that he left the interior arrangements.  Instead he turned to an external details.  We’ll look at those next week.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, page 64.)

Fortification Friday: “a redan or a lunette, is thrown up on the exterior to cover the outlet”

Before we close the discussion of openings for forts (see what I did there?), let me circle back to compare Mahan and Wheeler in regard to one of the fine points considered.  That being the use of a detached redan or lunette in advance of the outlet.  Recall that in pre-war writing, Mahan suggested:

In very frequented passages, a redan or a lunette, is thrown up on the exterior to cover the outlet, and thus ensure its safety in case of surprise.

And Wheeler, in the post-war, mentioned a similar arrangement, but perhaps narrowed the application to those larger outlets, for sorties, where simple interior traverses would not be practical.

Mahan offered two figures that illustrated the redan to the front of an outlet:

PlateVIIFig48_49

Figure 48 offers a wide redan in front of an outlet, which is further covered and flanked by by the “horns” of the larger work.  A very well protected outlet, we might say.  Mahan considered this a Redan Line.

On Figure 49, we see much more complexity.  Particularly with the defensive lines of fire.  The outlet is nested within a redan of a larger line.  On both sides are faces within redans of differing angles. This is considered a Tenaille Line – a proper definition we will discuss later.  But the point being the covering redan, to the front of the outlet, was absolutely necessary here in order to protect that weak spot.  The covering redan is somewhat off center of the outlet, perhaps to limit exposure at the expense of accessibility.

Wheeler, as you may recall, gave us only a simple rendition of the covering redan:

WheelerFig51

The question I have in regard to these advanced, detached “parts” covering openings is… just how often were these employed during the Civil War?

When examining surviving earthworks, we often find the area around the outlets obliterated.  Sometimes, due to necessity, that is done to facilitate visitor access.  But more often, just a case where the structures around the outlets were the most susceptible to erosion.

And when examining wartime plans, we see some use of these redans… but more often not.  Consider Fortress Rosecrans outside Murfreesboro:

FortressRosecrans

This was, some have said, the largest fort built during the war.  And in this plan we see examples of many features suggested by Mahan.  Specific to the outlets, we see up near the top that Battery Cruft was a detached lunette (maybe a “half lunette”) covering an outlet.  Elsewhere, such as next to Lunette McCook at the bottom right, we see an outlet (an existing road) without a covering redan or traverse.  Though we do see obstacles erected to the right of Lunette McCook.  And certainly that named work was positioned to dominate the approaches to the outlet.  Furthermore, what you don’t see in my “snip” are works in advance of the fortress that covered the railroad and road.  Though those were oriented south and not regarded as covering the outlet in question.

Another plan to consider is from Virginia, at Deep Bottom:

DeepBottomSnip

Here we see five road crossings at the main line of the works.  One of those is blocked entirely by a redan.  The other four (including one that appears to be a path cut just to clear a redan) have no traverses or covering works.  Just obstacles placed in front.

If we are assessing the protection of outlets, with Mahan’s suggestions in mind, we find a mixed application of those covering redans.  Seems to me the use of that sort of feature was based on the engineering assessment of need.

Now considering such use under Wheeler’s suggested implementation, let’s look to the location of a few large scale sorties.  First, how about the works were the Crater assault was mounted:

CraterSector

And further around the lines, and further forward in the historical timeline, to the sector around Fort Mahone:

FortMahoneSector

And to the left of that sector near where the Federal Sixth Corps mounted their sortie:

FortWelchSector

Now the scale of these maps mean these are not so much “plans” as operational maps.  So we know there are structures that escaped the pen here.  But what stands out, with double underlines, is the use of something far more elaborate than Mahan and Wheeler discussed.  We see entire sections of works advanced in a manner to provide staging grounds for those formations preparing for the assaults. Major assaults, mind you, involving whole divisions.  These were, you see, works built for the offensive.  Grand offensives!  In that light, might we say the entire Federal line was one large “covering work” in front of an array of staging areas and supply depots?

Fortification Friday: Outlets evolved in the post-war instructions

Earlier we considered the pre-war instructions offered by Mahan in regard to outlets, particularly how those would be constructed.  Training cadets before the war, Mahan covered the topic with a few paragraphs.  Later, after the war, he added a section about bridges associated with the outlets.  However, by the 1880s, Junius Wheeler’s instructions to cadets would sprawl over the better part of seven pages.  Maybe this is simply a case where pre-war there was a premium on copy space for printed manuals.  On the other hand, maybe Wheeler felt “his” cadets needed “special help” getting this particular aspect of fort-building in order.  Or perhaps, which I tend to think, wartime experiences prompted the extended emphasis.

The first thing we see with Wheeler’s treatment of the subject is a focus shift.  Before discussing the construction of these outlets, he steps back to discuss what these are used for.  Notably, the section is titled “Communications, barriers, etc.”:

Communications. – The defenders of a closed work must have arrangements made by means of which they can enter or go out of the work when necessary. In the case of continued lines, arrangements should be provided by means of which the defenders can make sorties.

Word choice here.  Mahan’s writing pressed that outlets were important for servicing the works.  Left unstated, implied at best, were other uses for the outlets – communications, logistics, reconnaissance, or simply just getting out to stretch the garrison’s legs. On the other hand, by selecting this sub-heading, Wheeler set different functional requirements… although, much vaguer than Mahan’s.

Wheeler’s second paragraph discussed the basics.  The outlets had to be made through the parapet, and that created a weak point in the work.  To minimize the risk, he insisted the number of outlets be kept to a minimum and built where least exposed.  Specifically, he gave these suggested placements:

In redoubts, the outlets are on the sides least exposed to attack; in half-enclosed works, they are placed near the middle of the gorge; in forts, they are usually placed near the re-entrants.

And that matches well to Mahan’s suggestions from decades before.  But where we see variations is with the size of these outlets, which Wheeler relates based on functional requirements:

A passage for the use of infantry only should not, as a general thing, be less than six feet wide; for artillery, not less than ten feet wide; for sorties, the outlets in continued lines should be at least fifty yards wide.

See what happened here?  Wheeler took Mahan’s two size categories and then added a third, based on an additional use-case.  I think at this passage Wheeler is thinking back to works at Vicksburg or Petersburg or around Atlanta.  And in those campaigns, field works had become part of an offensive operation – be that a very deliberate siege at some levels, but more dynamic than an “According to Vauban” siege.  Again, not to say wide passages for sorties did not exist prior to 1861, but rather to say those took on different emphasis around about 1863-4… at least in the American context.

Demonstrating that the more things change, the more they tend to stay the same, Wheeler offered this diagram for an idea outlet through the parapet with masking traverse:

WheelerFig50

Yes, he ripped off Mahan.  But give him a little credit for adding more notations and giving us that nice profile on the right.  And he offered the lines (c and g, the “crossing” arrows through the middle) which were the enemy’s “extreme lines of fire”.  Those lines, Wheeler instructed, governed the length of the traverse (T).  Note how those lines are drawn off the corner of the superior slope of the parapet.

Toward that, Wheeler did add a lot more to the notion of masking the outlet:

The length of the traverse may be shortened by turning back the interior crest at right angles to its general direction, and extending it as far as the crest of the Banquette.

This “turn back” is indicated by “B” on the figure.  One on each side of the outlet.  Notice how that would send the lines of fire (again, lines c and g) into a tighter intersection, further back in the outlet, and thus reducing the area the enemy might fire upon. Such angles reduced, the traverse need not be so long.  All in all a nice functional flourish to the outlet design.

Beyond that, Wheeler offered other options that would reduce the vulnerability:

Instead of having a road along its entire front, the traverse is sometimes joined to the parapet on one side of the opening, as shown by the dotted lines b d and e f, in Fig. 50.

And such would mean only one “extreme line of fire” need be considered in regard to traverse length.  But that did mean traffic had a nasty chicane to deal with.

This is all good, but how about that fifty-yard wide outlet for sorties?

The method adopted to mask the interior of the work in this latter case, is to place the traverse opposite the outlet on the outside, and beyond the ditch….

The traverse in this case is usually broken, generally a redan in trace, with the profile of a parapet, but commanded by the parapet in rear.

Figure 51 illustrated this manner of masking:

WheelerFig51

Basically, if you have to provide a wide gap in the works, the only viable solution is to build a miniature work in front to cover it.  Keep in mind, such sortie outlets would be placed on less exposed sections of the line.  And of course, these would be covered by strong faces on either side.  Such would reduce the chance the enemy might target the outlet for their own “sortie”.  And the redan covering the front would further reduce the danger of direct artillery fire.  Note, however, you don’t see a traverse in the interior of the works to cover the sortie outlet.  The purpose of this outlet is to allow infantry in wide columns to emerge in quick order. Bad enough, though necessary, to have that redan in the way.  Putting a traverse on the inside would impose yet another choke point for maneuver… and yet another delay in an operation where time was critical.

Before leaving Wheeler’s discussion of outlets, we’ll also examine the evolution of barriers and bridges.  Furthermore, Wheeler introduced the notion of ramps within these outlets.  All interesting facets to consider with respect to the art of military fortifications.

(Citations from Junius B. Wheeler, The Elements of Field Fortifications, New York: D. Van Nostrand, 1882, pages 148-51.)

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.)