Fortification Friday: Blockhouses as Safety Redoubts in the Fort

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


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:


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:


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:


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: Bomb Proof shelters, as in “force protection”

Last week I pointed to a change… if we may, an evolution… in military practice based on experiences of the Civil War.  In that case, we saw a new class of “semi-permanent” fortifications introduced.  And beyond that, we saw several improvements and refinements of the facilities constructed for fortifications, be those temporary or semi-permanent.

Now let us look at another evolution, just as subtle.  But one I would submit was a major change in the function of fortifications.  In his 1870 instructions, Mahan moved immediately from discussion of magazines into a similar structure with different function:

Bomb Proof Shelters.  Bomb and splinter proof shelters of wood have also been carefully built in the interior of some of these enclosed works, and in the gorges of those open to the rear; both may be arranged with loop-holes for defense. These are mostly constructed in the manner shown in Fig. 39, bis.

This brings us back to reference the shelter built on Morris Island the shelter built on Morris Island in the summer of 1863:


As related before, this was not necessarily a “new” structure.  Rather this was the use of a type of structure in a different manner, addressing an evolving requirement on the battlefield.  In this case, on Morris Island, the requirement was protection from shells and shrapnel delivered from high-angle or, as Mahan called it, curved, fires (or as I sometimes relate – fires acting on the vertical plane).  Overhead cover, we’d call it today.

Mahan gave a general description as to the construction of these shelters:

The exterior side is of heavy logs placed in juxtaposition, resting on a ground-sill and capped at top.  Parallel to these is another row, which may also be in juxtaposition or at short intervals apart and capped like in the outside row.  The roofing, consisting of heavy logs laid in juxtaposition and covered by thick jointed boards, rests on the capping.  The back face may be sealed on the inside to obviate the dampness from the earth resting against the back; and some simple method of drainage, by fascines or tiles, is arranged to carry off the water from the earthen covering.  This last should be the same as for the powder magazines.

So, these shelters were “like” magazines, but were not magazines.  The purpose of these shelters was to protect the troops, supplies, and equipment.  We’d call this force protection today.

But there is scant mention of this in the pre-war courses.  Here’s what I think (as in my thoughts… make sure you don’t get the idea I’m putting words in Mahan’s mouth…) – prior to the war, doctrine did not envision a situation where a field army would remain in postion subject to prolonged attriting fires.  Prolonged, as in more than a few hours.  Yes, things like mortars and howitzers existed prior to 1861.  And yes, during battle armies would be subject to fires from those type of weapons.  But, prior to 1861, the general perception was that sort of exposure would be limited, depending on the situation.  Perhaps only in a situation where an army was preparing a large scale assault… or preparing to receive a large scale assault.  So such exposure would be limited to a phase in a particular battle.

However, wartime experience brought with it a new perspective.  Entire campaigns would be fought with soldiers almost constantly in contact and exposed to attriting fires.  For emphasis, let’s just say in 1861, William T. Sherman led his command toward Manassas with the notion his troops would only be under fire (save some minor delaying actions) for a limited period of time on the battlefield.  But in 1864, he led a much larger force through Northern Georgia fully expecting the troops to be under fire every single waking hour.  An army could no longer afford to simply “lay in the open” waiting for the signal to attack. That wait might be for days, if not weeks.  And the artillery, of both sides, would not be idle.  We can offer many reasons this change occurred.  Regardless of cause, the effect was a need for better protection of the force.

Applied to practice of field fortifications, this brought a need for structures that would afford relief to the infantry.  Again, this is not to say such shelters did not exist prior to 1861.  Rather, such shelters were of little concern, prior to the war, for those constructing temporary, field fortifications.  However, by the summer of 1863, witnessed on Morris Island, these structures became necessary.  So much that a significant amount of manpower was diverted from other tasks in order to ensure “force protection” was given as the siege lines advance.  Oh… and so much that the defenders in Battery Wagner spent more time on shelters than on erecting more batteries.

And speaking of the defenders, Mahan added, with respect to the shelters:

It is highly important that these works should be so organized as to afford a retreat for the garrison should the main work be carried.  This might be done in some cases, by masking, with earth, only the lower portion of the side looking on the interior of the work, and covering the exposed timber with iron plating with loop-holes, to sweep all the interior space.

This sounds very much like a safety redoubt or keep…. but “sounds like” is not “the same as” in this case.  In his pre-war writing, Mahan proposed safety redoubts and keeps for field fortifications.  And he retained, those designations, even going further to elaborate on the construction of blockhouses as a form, even when proposing these shelters with arrangements for retreat.  The difference between here is the employment.  The keep was intended for a fortification with large interior capacity and for use as a last line of defense.  The shelters described, in the paragraph above, were employed even in smaller fortifications and were not necessarily the “last line” to defend.  The point being – shelters would protect the soldiers AND offer them a position from which to fight in conjunction with the localized defense within the fortification.  A keep was a shelter from which to rally and reform for the final defense of the entire fortification.

Not quite the trenches of World War I.  But the concept was in the air.

(Citations from Mahan, An Elementary Course of Military Engineering: Part 1: Field Fortifications, Military Mining, and Siege Operations, New York: John Wiley & Son, 1870, page 54-5.)

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.)