Fortification Friday: Wheeler and the evolution of interior arrangements during and post-war

I’ve mentioned on several occasions how the lessons on fortifications, used to teach cadets, demonstrate the evolution of doctrine from pre-war thinking into the post-war era.  We see some of this evolution when comparing pre-war and post-war versions of Mahan’s treatise.  But where the changes really come into play is when comparing Wheeler’s  1880 textbook.

An example of these changes is how Wheeler chose to relate details of interior arrangements.  Even when classifying these arrangements, Wheeler offered a shift, sometimes subtle, change of focus.  Recall Mahan’s pre-war text described the classes of interior arrangements as such:

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.

Somewhat brief, and from there Mahan proceeded to detail how batteries were placed on the parapet… with emphasis on the employment of artillery.

Wheeler offered a similar set of classifications, but abstracted those a bit with a mind to functional requirements:

Classes. – The earth work for the parapet being completed, and the revetments of the interior slope constructed, attention is then paid to the interior of the work.  Certain arrangements have to be made in the interior, to add to the efficiency of the defense, and to provide for the comfort of the troops who have to occupy the work.  These interior arrangements are divided into classes, according to the object to be attained by them.

The divisions may be classified as follows:

  1. The arrangements of, and along a parapet, intended to add to the efficiency of the defense;

  2. The arrangements within the area enclosed by the parapet, to shelter the men and matèriel from the fire of the enemy;

  3. The arrangements made to allow egress and ingress of the troops; including those made to guard the outlets against surprise; and

  4. The arrangements which may be made to provide for the comfort and welfare of the garrison when occupying the interior of the work for some time.

While Mahan named specific structures that would be constructed within the interior, Wheeler’s classifications come across is more so proper doctrine.  In other words, Wheeler put the reason before the task.  Such is a more formal approach to doctrine, as opposed to simply providing a list of structures, and  their specifications, to be used.

And with that approach, abstracted from naming particular types of structures, Wheeler was able to identify some of the needs, beyond the basics, of a garrison occupying a fortification.  You know… like those “comfort and welfare” things he mentions.  But not to be overlooked, shelter from enemy fire and ease of entry or exit.  These were all things Mahan addressed, but gave limited treatment. Did Mahan simply not care about the troops?  No.  But Mahan’s text was rooted in some pre-war concepts which, though we have discussed before, should be repeated for clarity.

Mahan’s instruction about fortification borrowed heavily from the European experience.  It was a textbook on field fortifications which would complement other instruction relying heavily, as is often the case with military science, on the “last war.”  Many scholars have debated the influence of Antoine-Henri Jomini on Civil War generalship.  But I don’t think we can dispute a “what would Napoleon do?” approach prevailed.

That in mind, the military minds came to make several operational assumptions.  With respect to fortifications, the assumption was two types would be employed.  Fixed, permanent fortifications were constructed to defend vital areas.  For the Americans, these were most often seacoast fortifications, as most potential adversaries would need to gain lodgement at some port (the exception, prior to the 1840s, being the northern border, but even there the great lakes presented a seacoast-like need).

The other form of defense assumed was temporary or field fortifications for use by an army on campaign.  And those were intended to work within the tactical framework handed down by the European experience on the Napoleonic battlefield.  These fortifications were employed to protect important areas related to the army’s campaign objectives.  And those objectives were subject to change.  The design of the works was more so to deter direct attack.  In that way the temporary works would deter direct attack, requiring a deliberate effort (i.e. a siege or other significant commitment of resources).  The temporary fortification was not designed for prolonged occupation or lengthy defense.  Above all, the temporary fortification was always a function of the campaign being undertaken at that moment in time.

The American experience, even before the war, offered a slight twist to the paradigm.  With a significant commitment to the frontier, structures such as blockhouses became important.  Yet the US Army did not give much instruction to that part.  In my opinion there were two significant reasons for this.  First, perhaps foremost, the methods for establishing frontier garrisons were judged as intuitive.  Mahan’s “Outpost” manual covered some of this.  Secondly, much of the responsibility for these frontier garrisons was given to territorial, state, or local authorities.  In short, it was not a major mission in the broader sense.  Rather, the US Army was supposed to give Congress detailed plans for defending the coast.  Those commitments out west were not the “big show”.

Civil War experience demonstrated the “two types of forts” assumption to be incorrect, to say the least.  Operational requirements demonstrated there was a third type which fell directly between the chairs.  That being a semi-permanent fortifications which were not directly tied to ongoing campaigns.  The best example of that would be the Washington defenses.  Lesser so the Richmond defenses, but of course those became the focus of a campaign later in the war.  Other examples, which we’ve mentioned in relation to blockhouses, were those works constructed to protect communications and supply lines. All of which supported the army in the field, but were not a direct function of that army’s operation… i.e. the campaign.   And as a function of those requirements, the engineers had to address other needs within the fortifications, to include “comfort and welfare.”

What I like about the passage from Wheeler enumerating the classes of interior arrangements is that he removed a lot of the Napoleonic baggage from the discussion.  Sure, forts were still built in the manner employed in the first quarter of the 19th century.  Men used shovels to dig, then pile the earth.  Fortifications still required parapets and ditches to be effective means of resistance.  The “physics” of the matter did not change, other perhaps than the need for additional thickness to resist rifled projectiles.  But it was the requirement those fortifications were filling that shifted over time.   That’s what I see reflected in the approach Wheeler gave to these particulars.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, pages 51-2; Junius B. Wheeler, The Elements of Field Fortifications, New York: D. Van Nostrand, 1882, page 114. )

Fortification Friday: Wheeler’s take on blockhouses

As we have often seen, when writing instructions for cadets in the 1880s, Civil War veteran Junius B. Wheeler put a twist or two on Mahan’s pre-war, and post-war, teaching about fortifications.  The blockhouse is yet another example of this.  For starters, Wheeler introduced the notions about using blockhouses with a different set of terms and classifications.  Instead of “safety redoubts”, Wheeler stated with…

Secondary interior arrangements. – Besides the interior arrangements which have been described, or mentioned, there are others which are secondary in their nature.  These are the arrangements which are to be used under certain contingencies, or in cases of emergency.  An example, would be  defense placed within a field work, which defense can be used only when the main work is no longer defensible, etc.

This is certainly keeping in line with the concepts we saw Mahan teaching, but is giving a broader sweep to things.  In the next paragraph, Wheeler jumped right to the blockhouse… but with some fresh considerations:

Block-houses. – It is frequently the case that a separate fortification is constructed, laying entirely within a work exterior to it, into which a garrison can retire and protract their resistance, even after the outer fortification has been taken, or has been made unfit for further defense.

If this interior work is a line of earthen parapet, it is called a retrenchment; if it is a defensible building, it is termed a keep.

The term, keep, is also applied to a work which is entirely separate and distinct from the work exterior to it, whatever may be the material used in its construction. In a field work, the keep is built of timber, and is called a block-house.

There you have it – in fortifications the engineer will consider “secondary interior arrangements” to include retrenchments and keeps.  And if the latter of which is made of timber, it is called a blockhouse.  It’s the same basic thing Mahan wrote, just using different terms.  But, as we all know, terms have meaning and are selected for reasons. In this case, I think Wheeler was simply saying there were many different options for these interior works, and the blockhouse was favored.

Regardless of the emphasis, Wheeler’s blockhouse keep differed little from Mahan’s in form and function.  Wheeler directed the blockhouse have “good command over all of the interior space” and “that all parts of the exterior work can be seen from it.” Wheeler’s blockhouse could be square, rectangular, and “even cruciform” in plan, just like Mahan’s.

However, there was some difference in the internal dimensions.  Rooms inside the blockhouse were to provide six feet of height, though eight or nine were suggested for ventilation.  And Wheeler suggested an interior width of nine feet, “as this is the least distance which can be used and give room for a passageway and a row of bunks.”  Recall, Mahan specified at minimum a nine foot height and a width of up to twenty feet.  But keep in mind Mahan’s dimensions were governed by the need for handling muskets within the blockhouse.  By the time Wheeler was writing, those Springfields had been converted to trap-door models.  Wheeler indicated the overall length of the blockhouse, including all rooms and spaces, would “depend upon the number of men it has to accommodate, after the width has been assumed.”

As to the thickness of walls, Wheeler gave no specification for single or double thickness of timbers.  Rather, he simply indicated, “Block-houses must be made strong enough to resist the projectiles which may strike them and should be proof against fire and splinters.”  Elaborating further, Wheeler said, “The conditions given for a bomb-proof are applicable to the block-house, with the additional one of arranging its walls for defense.”  And by defense, he meant loopholes.   To illustrate this, Wheeler recycled one of Mahan’s drawings:

WheelerFig53_54_55

So in form and function, Mahan’s post-war blockhouse remained the standard.

But what of Mahan’s “American blockhouse” for use as a stand-along fortification?  Well, Wheeler had a different label:

Isolated block-houses. – Timber blockhouses were used frequently in the war of 1861-5 in isolated spots, as independent works.

In these places, they were, as a rule, exposed to attack only from infantry or cavalry, or a few pieces of field artillery.

The construction shown in Figures 53, 54, and 55 is a type of these isolated block-houses.

It was found from experience that it required a thickness of forty inches of solid timber to resist the projectiles of field-guns.

These isolated block-houses were frequently built two stories high.  The upper story was usually placed so as to have its sides make an angle with the sides of the lower story. By this arrangement, the corners of the upper story projected over the sides of the lower.  This arrangement of the upper story removed the dead space near the sides of the lower story, and the sector without fire in front of the angles.  Block-houses exposed to artillery should not have a second story.

Again, very close to the words Mahan wrote, but mixing the pre-war with a bit of wartime experience.  There are a few points which followed in Wheeler’s text that we shall return to in time.  But for the most part, we see the “American blockhouse”, with a few new terms to describe its classification within the fortification form.

Wheeler’s manual was aimed at a generation of cadets some twenty years removed from the Civil War.  That generation would include men like John J. Pershing.  While some, as was the case with Pershing, would serve on the frontier where there was use for the old blockhouses.  And around that time, our romantic notions of the frontier posts took root.  So I close this discussion of blockhouses coming full circle to those movie props and toys which come to mind when that sort of fortification is mentioned.

(Citations from Junius B. Wheeler, The Elements of Field Fortifications, New York: D. Van Nostrand, 1882, pages 156-60.)

Fortification Friday: “Sufficient strength to resist” artillery taken on cavalry raids

Last week, we discussed Mahan’s American blockhouse and how that form of fortification became important during the Civil War.  During the war, the blockhouse became a common feature along railroads, roads, rivers, and other key points in the rear areas.  I don’t think this reflected a “brand new” use of the blockhouse fortifications, but rather one of greater significance as result of the needs of the war.

Pre-war thinking on such matters focused on a conflict against European powers, in a “War of 1812” scenario.  As such, the rear areas would be somewhat secure behind the Atlantic Ocean (with Mexico and the British in Canada assessed as more defensively oriented).  Only on the frontier would there be great need for blockhouses to secure supply and communication lines.  But the American Civil War upset that line of thinking.  With extended lines across half the continent, the armies could not expect to guard every quarter. This gave an opening for leaders with names like Stuart, Forrest, Wheeler, Mosby, and Morgan.  Yes, those glorious raiders riding about disrupting Yankee operations…

I would offer the Confederate raider threat reached its peak during the Atlanta Campaign.  Not to downplay other sectors, but the spring-summer of 1864 was somewhat a “point of no return” in many regards.  As a counter to the raiders, Major-General William T. Sherman directed the fortification of numerous posts along his supply and communication lines.  One of those we saw last week:

02151r

And as I pointed out last week, the blockhouse in the photo compares well to the figures offered by Mahan in his post-war manual:

MahanPage65Fig1_2

Assuming Mahan’s figures are indeed close matches, we can project all sorts of details not visible in the photo – such as internal arrangements.  And thinking of those, we have the other half of Mahan’s illustrations to consider:

MahanPage65Fig4_5_6_7_8

Now we might say a picture is worth a thousand words.  If so, I’d offer these detailed figures are worth a couple thousand more. Figures 4, 5, and 6 give us a measure of the loop-holes on the lower story.  Figures 7 and 8 provide the same for the upper story.  One might dismiss the details as simply “common sense.”  But my counter would be that “common sense” is usually derived from experience.  And in this case, the manual attempts to impart some experience onto inexperienced cadets… who definitely needed sage advice based on wartime experience.  Besides, as I like to say on such matters, “it goes to show us how THEY did it.”

The caption provided for this page of figures further solidifies the linkage to wartime experiences:

Figs 1, 2, 3, etc., represent the chief details of the two-story block-houses that have been adopted for the defense of railroad stations, bridges, etc., along the line of communications of General Sherman’s Army.  From experiments made upon them, the lower story, with its double row of heavy logs from three and a half to four feet in thickness, is regarded of sufficient strength to resist the field artillery usually taken with cavalry on their raids.

And that was the goal – a “keep” for an outpost garrison that would afford protection against the raider’s weapons.

Now some will point out that Forrest and Wheeler captured their fair share of blockhouses while out raiding.  I would offer that in most cases those captures involved a pause of action under a flag of truce.  Words like “… to prevent further effusion of blood” were mentioned.  So we might contend the blockhouse did indeed serve the “keep” function even if the garrison were captured.

(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 65.)

Fortification Friday: Mahan’s suggestions to improve blockhouses

When it came to fortifications, Professor Mahan held to the “you can never do enough” principle. As we’ve discussed in preceding posts, in a field fortification the blockhouse was the keep, or last point of defense for the garrison.  It was to be outfitted in such a way that the garrison could cover the parapet with fires.  And interior arrangements would grant ample space for handling weapons.  But more could be done to improve the blockhouse.  First and foremost, one should surround the structure with a ditch:

The block-house is surrounded by a ditch, similar to one used for a defensive stoccade. A strong door is made in one of the re-entering angles, and a slight bridge leads from it across the ditch.

We saw this arrangement along a profile line in the illustrations:

PlateVIFig43

Somewhat analogous to the ditch-parapet in profile, with the blockhouse structure itself being the parapet.  Notice the glacis in front of the ditch.  And also the palisade in the ditch to the left. And we have those heavy doorways, conforming to the structure prescribed for outlets.  It’s all coming together here for the keep.

But we were still not finished making the blockhouse unassailable. There was more that could be done.  Perhaps a structure on top from which the garrison could fire down onto the attackers?

It has been proposed to place a slight parapet of earth on top of the block-house.  It is thought that this accumulation of earth would be too heavy for the timbers, independently of leaving but little space for the defense.  Perhaps a better arrangement might be made on top, similar to a defensive stoccade, the uprights being secured at bottom, between two pieces resting on the top pieces, and held firmly by an arrangement of riband pieces and braces.

Mahan’s method would provide a lightweight structure, sufficient to stop musketry.  Artillery, though, might turn that blockhouse parapet to splinters. So, any suggestions to counter that?

It has also been proposed to place the the interior and exterior rows of uprights three feet apart, and fill in between them with closely packed earth, for a defense against artillery.  This method has been tried, and was found to be less solid than the one here laid down, independently of being more difficult to construct.

Recall, the guidance stated earlier was to use two thicknesses of twelve inch timbers for defense against field artillery. This was seen as more sustainable, with less physical footprint, as what would amount to packed earth at steeper than a natural slope.

Other techniques to improve the blockhouse included methods to make the enemy’s closure even more difficult.  “The top pieces should in no case project more than twelve inches beyond the sides, to admit of logs, &c., being rolled over on the enemy.”

And if that was not enough, one could stack up a second floor (somewhat as we saw from the colonial era Fort King George):

The block-house is sometimes arranged with two stories, the corners or the sides of the upper story projecting over the sides of the lower. Either of these methods is sufficient for the defense of the lower story; but the first is the best to procure a fire in the direction of the angles.  It can only be used, however, as a defense against infantry.

When artillery cannot be brought to bear against the top of the block-house, it may be constructed like an ordinary floor, and be covered with nine or twelve inches of earth to guard against fire.

Of course, where artillery might be brought to bear against the blockhouse… well let us just say a lower profile was preferred.

But, Mahan was tapping on this point about “places where artillery will not be” for a purpose.  He was looking toward the “west” of that era:

The application of wood to the purposes of defense is one of paramount importance in our country.  A block-house, surrounded by a defensive stoccade, is impregnable to the attack of infantry if properly defended, and is therefore peculiarly suitable to either wooded or mountainous positions, where a train of artillery cannot be taken without great labor, owing to the impediments that may be thrown in its way, by rendering the roads impassible from obstructions easily obtained.

Of course, just couple of decades after Mahan’s writing armies backed with steam power (rail and river) were able to overcome many of the natural impediments of the Western Theater.  Still, the suggestion held some merit further to the west, where most potential adversary possessed only light artillery. Oh, and the mountains were much higher.

And Mahan also saw an application for the blockhouse in the east, where pre-war thinking was focused on attackers that arrived by ship:

In positions covered by extensive earthen works, such as those that would be required for the defence of the towns on our sea-board, and which would be occupied during a war, a defensive arrangement of the barracks for the troops, so that they might serve, in case of the main works being force, as rallying points, under cover of which the main body of troops may retreat with safety, is a subject that commends itself to serious attention of the engineer.  From the details already entered into, an efficient combination for this purpose will suggest itself to the reader, without entering farther into particulars.

Such arrangements might have been of use for Confederates defending the Carolinas, Georgia, Florida, and the Gulf Coast.  We might contend the inner defensive lines at Charleston served the purposes of a keep in this regard.  But here again technology had rendered the blockhouse less useful.  By 1863, Federals could bring to bear rifled artillery of the largest caliber wherever they might encounter a blockhouse.

Yet, while we can say rifled artillery and means to transport such weapons rendered the blockhouse less desirable, we still can point to widespread use of such structures throughout the Civil War.  In particular along lines of communication.  In those rear areas, raiders were not likely to bring more than a handful of artillery pieces.  And that experience lead to some shifts in the instruction about blockhouses as field fortifications… which we shall discuss next.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, pages 64-6.)

 

Fortification Friday: Square, rectangle, or even a cross – blockhouse forms

Last week, we introduced the blockhouse as an interior structure, perhaps better classified as a facility, within a field fortification.  Allow me to stress again, the context of Mahan’s writings in “Field Fortifications” about blockhouses was scoped to discuss the use of those sort of structures in conjunction with larger works.  It was not to say blockhouses would always be used as such, nor to dismiss other sorts of employment of that fortification type. This particular Mahan lesson (of which there were many, across several manuals, as we must recall) was focused on building a “keep” so the defenders might “keep” something valuable… their lives in the event all was lost.

Having discussed the concept and general layout of the blockhouse, Mahan turned to particulars:

With regard to the details of the construction, the timber for the sides should be twelve inches thick, to resist an attack of musketry, and to resist field-pieces, two feet, in which case the sides are formed of two thicknesses of twelve-inch timber. If the timber is placed upright, each piece should be let into a mortise in the cap-sill; and every fourth piece of the top, at least, should be notched on the cap-sill, to prevent the sides from spreading out.

This would form, in essence, the walls of the blockhouse.  Notice the prescribed thickness, in regard to the expected threat – be that musketry or artillery.  I would add that with the introduction of rifled artillery, the two foot thickness was insufficient.  But there begins a point of diminishing return. How much more timber should one add to the blockhouse, thus subtracting usable interior space, in order to defend against an Ordnance or Parrott rifle?  Ah… a question best addressed when we consider the post-war manuals!  So let’s hold that thought.

I do wish Mahan had included a good illustration of the proposed arrangement of timbers. And I’ve not located any other contemporary illustration to serve.  But the general idea is apparent… perhaps for generations who suffered the splinters from Lincoln Logs, if not so much for those of more recent times and their Lego bricks.  We will revisit the arrangement of timbers in the walls for the post-war manuals.

Moving forward, we need to consider the layout of those walls and how best to arrange the blockhouse in order to meet requirements:

The plan of the block-house must conform to its object generally; it may be square or rectangular.  If flank defenses are required, its play may be that of a cross. The interior height should not be less than nine feet, to allow ample room for loading the musket; this height will require that the timber of the sides shall be twelve feet long, in order to firmly set in the earth.  Sometimes a ground sill is placed under the uprights, but this is seldom necessary.  The width may be only twelve feet in some cases, but it is better to allow twenty feet; this will admit of a camp bed of boards on each side, six-and-a-half feet wide, and free space of seven feet….

So the layout, as seen from above, could be the square form familiar to us from the playsets of yore.  Or could be extended or expanded to use other layouts as tactical needs demanded.  The layout tended to employ right angles, however.  We look back at Figure 44, which is somewhat a cross, in plan:

PlateVIFig44

Notice how the dimensions are governed somewhat by the need to provide space for handling muskets.  Form will follow function.  The most important quality of the blockhouse, as a keep, is to allow the garrison to create a pause in the action, should the parapet be lost.

But “camp bed”?  Yes, that implies a place to sleep. But it was also a defensive arrangement.  “The camp bed serves also as a banquette; it is placed four feet three inches below the loop-hole, and has a slight slope of about eight inches inwards.”  Notice how the interior arrangement is to provide, in terms of wall to wall floor space, for a 6 ½ foot wide camp bed on each side with open space for seven feet between.

Now everything thus far has implied the garrison would only have muskets in the blockhouse.  Let us make arrangements, then, for artillery:

If cannon is to be used for the defense, the width must be at least twenty-four feet; this will allow eighteen feet for the service of the gun, which is generally ample, and six feet for a defense of musketry on the opposite side.  A greater width than twenty-four feet cannot well be allowed, because the bearing would be too great between the sides for twelve inch timber; and even for a width of sixteen feet it would be well to support the top pieces, by placing a girder under them on the shores.

Basically, bigger guns require more space.  So we adjust the arrangements.  But there is a physical limit as to how much more space is allocated.  If a really large blockhouse were built, it would require substantial structural reinforcement.  Better to stick with a single cannon per side, if used at all.

Since these arrangements place emphasis on affording space to handle weapons, be that musket or cannon, we need to discuss the loopholes in detail.  We’ll turn to that in the next installment.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, pages 63-4.)

Fortification Friday: Blockhouses as Safety Redoubts in the Fort

When I say “blockhouse” many of you might be thinking about favorite childhood playsets:

OLYMPUS DIGITAL CAMERA

Certainly suitable for the defense of the bedroom in the face of the elite Confederate Plastic Brigade, or perhaps the indigenous Plastikawi tribe.  But… something that could not hold against the Green Army Men armed with bazookas and flamethrowers.

Kidding aside, the playset fort is pattered after real structures from American history.  The blockhouse was not unique to America, as it was a form brought over by Europeans.  However, the blockhouse became the preferred fortification on the North American continent from colonial times right up to the 20th century.  Blockhouses work well in situations where the enemy is unlikely to possess anything larger than light artillery.  The interior of the blockhouse was easily adapted into living quarters.  Conversely, living quarters (houses) might be easily adapted into a blockhouse.  Those, and other qualities, made that form of fortification popular on the frontier.

The popular image of a blockhouse is something made of wood.  But stone, or even adobe, might be used instead.  Since wood was in abundance on the early American frontier, we tend to see a lot of structures like this one:

Ft King George 3 Aug 11 1273

This is recreation of Fort King George, Darien, Georgia (a place with many, many layers of history).  In this particular case, the blockhouse served several roles – a high observation platform over the marsh, a platform for covering fire to protect approaches to the fort, and, in the event the works were overwhelmed, a final defense for the fort’s garrison.

It is that last function that Mahan had in mind when considering interior arrangements for field fortifications.  Blockhouses were a structure that could be used for what he called “safety redoubts”:

Safety Redoubt.  In enclosed works a place of retreat, into which the troops may retire in safety after a vigorous defense of the main work, will remove the fears of the garrison for the consequences of a successful attack of the enemy, and will inspire them with confidence to hold out to the last moment.

This interior work, which may be very properly be termed the keep, can only be applied to works of large interior capacity.  It may be formed of earth, or consist simply of a space enclosed by a defensive stoccade, or palisading.  In either case it should be about four feet higher than the main work, to prevent the enemy from obtaining a plunging fire in it from the parapet of the main work.

Let us pause here before going to Mahan’s formal introduction of the blockhouse.  This “hold out to the last” is a notion steeped in 19th century presumptions about how a siege would play out.  A garrison “holding out” would force the enemy to make a direct attack on the parapet… in other words, to get up close, personal, and… well… very violent with the defender.  And in that violent melee, the defender was not exactly in a position to call a “time out”.

The safety redoubt, or keep, was a place to retreat and, more importantly, force a pause in the action.  And from the keep, within that pause, the defender might negotiate a cessation of the fight, with honor.  Thus we see how that might allay fears of “consequences” for the garrison.

That in mind, Mahan offered his preference for the keep:

The best arrangement for the keep is the construction termed the block-house. This work is made of heavy timber, either squared on two sides or four; the pieces which form the sides of the block-house are either laid horizontally, and halved together at the ends, like an ordinary log-house, or else they are placed vertically, side by side, and connected at the top by a cap-sill. The sides are arranged with loop-hole defenses; and the top is formed by laying heavy logs, side by side, of the same thickness as those used for the sides, and covering them with earth to the depth of three feet.

Mahan offered this figure as an example of a blockhouse:

PlateVIFig43

This perspective is looking at the blockhouse along with a cross section of adjacent works and structures.  Rather busy.  This section is along the line a-b from Figure 44:

PlateVIFig44

The combined caption reads:

Figs. 43,44. Shows the plan and section of a block-house of upright timber.  The plan is made to exhibit a portion of the top complete; the timber covering the top; the arrangement of the cap pieces; a plan of the loop-holes; and a plan of the camp-bed. Fig. 43 exhibits, in a like manner, a cross section of the block-house and ditch; with interior and exterior elevation.

We will go into the particulars for construction in later posts.  What is important to identify here is the functional nature of this blockhouse.  Just as with the colonial-era Fort King George, we see a blockhouse adjacent to a ditch and other defensive structures.  One might say the blockhouse filled up the fort’s interior.

For an attacker, this presents a serious tactical problem.  One might defeat the defender on the parapet.  But the parapet would be a dangerous place to make a living with the blockhouse overlooking all. So you see where a “pause” would be in order.

Keep in mind, within this discussion of keeps, Mahan was not stating or suggesting that blockhouses only be constructed within and in conjunction with elaborate field works.  Rather that he offered that a blockhouse was a structure that served well as a keep inside a larger set of works.  We see that usage applied by his students during the Civil War.  Looking back again to Fortress Rosecrans:

FortressRosecrans

We see Redoubts Schofield, Brannan, T.J. Wood, and Johnson within the interior.  One wartime report described the arrangement as, “… strong against attack, being defended by large keeps, which deliver their fire upon every part of the interior.”  I would further add that most of the lunettes on the perimeter of this vast fortress included blockhouses.  So there were multiple “keeps” within a depth of the defense.  Keep in mind the scale of this fortress.  The safety redoubts, named above, were armed with 30-pdr Parrotts and 8-inch siege howitzers.  The Confederates would need to bring a large amount of iron in order to suppress the fort’s garrison.

But the size of this work was perhaps its weak point.  After the Army of the Cumberland moved further south, through the summer of 1863, there the need to keep this fortification in order was taxing, in terms of manpower. An 1865 report suggested all be reduced to simple blockhouses covering the bridge and depots.

That circles back to the point about blockhouse usage.  As said before, Mahan was not suggesting the only place to use a blockhouse was as a fort’s keep. But as his text was focused on field fortifications, the focus was on that function.  We will see blockhouses enter the conversation in regard to detached defenses in particular.  Furthermore, the post-war instructions would place more emphasis on the detached, singular blockhouse.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, pages 62-3; OR, Series I, Volume XLIX, Part 2, Serial 104, page 502.)

Fortification Friday: Barriers, Bridges, and Ramps … the fort “communications” infrastructure

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:

WheelerFig52

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.)