Fortification Friday: As Wheeler would say, “Loopholes are not just for blockhouses”

As we continue to compare and contrast the pre-war writings of Dennis H. Mahan with the post-war instructions of Junius B. Wheeler, let’s move from arrangements for the artillery to that of the infantry on the parapet.  Mahan, like his contemporaries, left the infantry on a bare parapet, with a firing step on the banquette that would allow them to step-up to the crest and fire over.  Little else was deemed necessary.  But experience of the Civil War indicated something more was indeed necessary.   Wheeler discussed this under the heading of “loopholes”:

Loop-holes.  – Troops on the banquette, when in the act of firing their pieces, are frequently exposed to the fire of the enemy’s sharp-shooters.  Under these circumstances, expedients must be devised to protect the men, without interfering with their fire.  The expedient which is most generally used, is that of an improvised loop-hole.  The loop-hole is made, in this case, by arranging two or more rows of sand bags, placed upon the parapet and filled with earth, so that the top row will be higher than the men’s heads, and so as to leave intervals between the bags in the lower rows, through which the men can aim and fire their pieces.

Figure 28 illustrated this arrangement:


Let’s walk through this passage, as it offers another glimpse into the changing doctrine applied to the battlefield.  Right from the start, we see something “non-Mahan” as a condition.  In those pre-war days where the Napoleonic battlefield framework was in play, musketry was generally used in mass.  Volley fire, by attacker and defender, was the expected means of delivering those lead projectiles.  In that framework, working a musket into a gap in sandbags would slow down the delivery of a volley.

But Wheeler alluded to a change in how musketry was used.  Instead of massing fires in volleys, the Civil War armies employed much more individual fires.  Skirmishing, of course, took on greater importance.  And in these field fortifications, that translated to sharpshooting.  More likely the attacker would employ this means of attriting the defender, instead of attempting a rush of the works.

This is not to say nobody ever thought of putting sandbags on the parapet before the Civil War (or headlogs, which we’ll circle back to).  But this is to say changes in the way musketry was delivered brought out a need to employ this feature (loopholes) as a standard fit on the parapet.  Wheeler and his contemporaries didn’t invent the sandbag loophole.  They simply introduced it to meet an evolving requirement.  Yes, “innovation” does not always mean “invention.”

There were other ways to setup a loophole on the parapet of course:

Gabions are also used for a similar purpose.  The gabions are placed in pairs upon the parapet and filled with earth, each pair being separated from the adjacent pair by an interval of about two inches.

And… field experience gave us even more options:

A contrivance adopted in the war of 1861-5, was quite effective for the same purpose.  Skids were placed upon the parapet, with notches cut in them.  A heavy log was placed on the skids, occupying a position parallel to the interior crest and just in contact with the superior slope.  Notches were cut in the underside of this horizontal log and these were used as loop-holes.  The openings to the exterior were made as small as possible, and in some cases were protected by small patches of boiler iron spiked upon the log.  When exposed to artillery fire, earth was banked against the log.

We often hear this or similar arrangements called a “head log” in the writings of veterans.  I am most curious that Wheeler didn’t use the term.  And even more curious why Wheeler didn’t include an illustration!  At any rate, he continued with this description, naming an “innovator” from the late war:

A wooden loop-hole was devised by Lieut. King (now Major) of the United States Engineers, which was used in 1864.  It was practically a wooden hopper made of boards, placed upon the superior slope of the parapet, and covered with earth.  The splay of the sole and the angle of the cheeks were made to suit the field of fire required.

The officer mentioned was Lieutenant William R. King.  Brett Schulte has King’s report on Beyond the Crater, and a detailed report it is.  The accompanying illustration matches to Wheeler’s description.  For brevity, I’ll refer you to Brett’s excellent site.

Wheeler continued, with detailed requirements for these loopholes:

The exterior orifice of a loop-hole for musketry should be made as small as possible.  A width of two inches and a height of five, is sufficiently large for ordinary purposes.  The sides are sloped, and an inclination given to the bottom and top, according to the field of fire which is to be swept.

Now what is good for the musket should also be good for the cannons, right?  Of course:

Embrasures are sometimes protected in a manner similar to this arrangement for loop-holes.  Timbers are laid across the embrasure, covering the throat, leaving only room for the muzzle of the piece.  These timbers are then covered by sand bags, by fascines, etc., to make them shot-proof.  Sometimes the embrasure is filled with sand bags or fascines to mask it, these things being quickly removed when the embrasure is needed for use.

Thick wooden shutters, made bullet-proof, and placed on vertical axes, and iron shutters swung on horizontal axes, have both been used to close the throat of the embrasure.

In some cases, timber supports were extended back from the parapet and a covering of timber and earth placed upon them, protecting the gun from vertical and plunging fire.  A gun thus sheltered is said to be case-mated.

Again we see the factor driving all this “innovation” and change – different types of fire were employed.   Individual musketry … sharpshooting as it may be called… brought out the need for protection on the parapet.  Vertical and plunging fire, which I have written about before, brought out the need for overhead protection.  No new inventions are introduced here, rather the innovation lay in the way existing practices were employed.

(Citations from Junius B. Wheeler, The Elements of Field Fortifications, New York: D. Van Nostrand, 1882, pages 126-8.)


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.)