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:


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:


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:


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:


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 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:


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:


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:


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:


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:


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.)