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.)