Fort Johnson Photo Analysis, Part VIII: Over a hundred 90-pound bolts to deal with Federal monitors

In the last installment in the walk around Fort Johnson, I offered up this diagram indicating the perspective of several photos of the interior of the fort:


Let me pick up this tour by stopping at point labeled FJ6 on that diagram.  That is where the photographer setup his equipment for this photo:


We are looking into the gallery where a 7-inch Double-Banded Brooke Rifle sits.  This is the same weapon appearing in photo FJ2 on the exterior of the fort.  What I like most about this view is that the line of sight is parallel to the profile line used by the surveyor’s diagram of the fort’s profile:


“Section 2” in the diagram above was along a line drawn through the right-most gun position.  The FJ6 photo looks down the position to the left of that line.  And keep in mind that “Section 1” runs perpendicular to the line of Section 2 and thus the line of sight in photo FJ6.  Sure, you say, what is there to be excited about?  Well this allows us to visually confirm… or reject … some of the particulars of the survey.  So let us pay attention the those profiles…


What catches my eye is the slope of the “V” that forms the gallery here.  The survey, since it used crisp lines, indicates the works had a “V” with a crown on each arm.  Almost a “V” within a “V.”  What we see in the photo is an eroded version of that.  A crown exists, but the slope is more of a gradual curve down to the base of the “V” and not offering a distinct shelf or shoulder where the crown meets the base.  Surveyors’ “license” perhaps?  No.  I think the surveyors accurately depicted what they saw.  But theirs were trained eyes, experienced by four years work with earthworks in the field, to know what the profile was designed to be.  And those surveyors were quick to extrapolate from the effects of weather, erosion, and neglect to show how the works were originally built.  After all, the survey was part of a report that needed to demonstrate how formidable these works were, and not intended as a study in shifting of sand.

That all said, let’s look at what would be the “star” of this photo – that big rifle:


Notice the cuts into the carriage, on both cheeks.  Also notice the quoin for elevating the gun.  This gun is pointed to the waters between Forts Sumter and Moultrie.

Looking down at the table supporting the gun, there are tick marks along the edges.


The tick marks below the race appear distinctly in the “sunny side.” But faintly along the edge of the race where the sun is directly on the wood.  However, under the shadow of the carriage, the opposite is true.  So as we consider where the gun was pointed, we have some indication as to how the gun crew ensured the weapon was on target.  The Confederates did conduct practice fires, which we call “registering” today, against targets in the harbor.  And of course they had feedback from the many counter-bombardments of Federal targets on Morris Island. So you might say those tick marks were “earned” along the way.

I would be remiss without calling out the barrel, which serves as a convenient mark to associate several photos.  We can also examine the texture of the fort’s walls.


Moving back a bit from the gallery, let me look through from left to right.  On the far left is the end of a railing.  What we will see from some of the other photos is that this rail served as an anchor for ropes extending from a tent.


To the left of that rail is a wash basin.  It’s a metal basin, perhaps tin, as we can see the metal seam up the side.


But since this is “To the Sound of the Guns” and not the “Civil War Field Hygiene” blog, we are going to look past that wash station at the pyramid of Brooke bolts:


These bolts have a square headed nut for the bolt attaching the sabot to the body.  We’ll see from another view there is a space between the sabot and the body.  There are two bourrelets (the band around the projectile used to align it to the bore), with one at the base and another towards the front.

One of the bolts in the stack is missing its sabot:


I’m not as good with projectiles as I am with cannons.  But I think these are “Tennessee” bolts, known to collectors as “Type II.” There are four holes in the base of the bolt.  One of those is filled by the bolt used to retain the sabot.  The other three, spaced around the middle of the base, are indentations that matched up with lugs on the inside face of the sabot.  The way this worked – when the Brooke was fired, the expanding gasses would push against the copper sabot and thus force the concave outer face to seal against the bore and into the rifling grooves of the bore.  That also forced the three lugs on the inside face of the sabot into the three holes on the base of the bolt.  With the copper sabot pressing into both the rifle grooves and into the holes, the spin of the rifling was imparted to the projectile.  And we can see all the parts for that system, save the rifling of the bore, in this photo.

Projectiles of 7-inch caliber were produced in Charleston and also brought in from other sources.  The bolts were used from both the 7-inch Brooke and rifled 42-pdr guns.  These were intended to counter Federal monitors.  Though, with their mass, the bolts would have crashed through any wooden vessel with ease.  We see fifty-six of these stacked to one side (two pyramids of bolts, stacked nose to nose).  To the other side of the gallery, there is another pyramid of bolts, these stacked tail to tail:


Here we see the flat faces of the bolts.  Not designed for aerodynamic efficiency, these flat faces were meant to impart the most force upon iron plate.  These projectiles didn’t pierce, rather were designed to shatter or bend the plate.  Purely a mass times velocity equation.  Each weighed just over 90 pounds.  And we are seeing over 100 of these bolts.  A lot of mass that would have been thrown at any Federal monitors trying to force passage into Charleston.

The top three projectiles have markings:


“A C” … which I am at a loss to explain.  But those top three bolts, with markings, appear in another photo.  So they are good placemarks as we “tour” the fort.

As we “walk” to the next point along our “tour,” we’d have to step over some weeds growing up in the fort:


A reminder that this photo was taken in the spring of 1865.  Weeds and grass were taking hold over the fortifications of a war in the closing stages.


3 thoughts on “Fort Johnson Photo Analysis, Part VIII: Over a hundred 90-pound bolts to deal with Federal monitors

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