Fortification Friday: Let’s put more guns in barbette batteries on the bastion

Last Friday we walked through the process of placing a gun, in a barbette battery, to cover the capital of a bastion (in other words… at the point of the salient).  Such is a significant improvement of a defense, as it allows the defender to put firepower on the “sector without fire” and address one of the inherent flaws of the bastion.  If setup by the numbers, the emplacement looked as such (ignore “Figure E” to the left for the moment):

PlateIVFig32W

Such is good news for the defender.  But the artillerist is quick to point out, that’s a rather exposed position.  To cover that gun on the capital, the defender would want to place additional guns in the bastion, on the faces.  This would not only afford counter-battery fire on any attacker cannon aimed at the point, such would also bolster the firepower of the faces of the salient.

With that expressed need in mind, consider the next paragraph from Mahan:

If three more more guns are placed in the salient, a pan-coupé is formed as in the last case, and twenty-four feet are in like manner set off on the capital but instead of proceeding as in the last case, a perpendicular is drawn from this point to each face, and the pentagonal space, thus enclosed, will be taken for the gun in the salient; from the perpendiculars last set off, as many times sixteen-and-a-half feet will be set off on the interior crest of each face, as there are guns required:  this will give the length of the barbette along each face; the depth will be made twenty-four feet, and the two will be united in the salient.  One of more ramps may be made as most convenient.

So to add those additional guns, we start with the barbette on the capital as established before:

PlateIVFig33_A

Note here the ramp is removed from the first barbette, so we have a pentagon to work with, instead of a hexagon.

Next step is to allocate space to the sides of that pentagon on a parallel of the parapet:

PlateIVFig33_B

This is 24 feet back of the parapet, to confirm to the depth of a standard barbette. Note this is the “mound” or built up area prescribed for a barbette, and should bring elevation up to at least “two feet nine inches below the interior crest for guns of small caliber, and four feet for heavy guns.”

Next the engineer would allocate a frontage of 16 ½ feet (what Mahan wrote) or 18 feet (what Mahan put on his diagram) for each gun:

PlateIVFig33_C

Confusion over the correct dimensions?  Not really.  Recall 16 ½ feet was for field guns and 18 feet was for siege guns. Both requirements appear to be offered interchangeably in the instruction.  In those frontages, we see the platforms (C) for the guns.

With those defined, in the case of our diagram, there are two barbette positions on each face:

PlateIVFig33_D

But… how do we get the guns up there?  Oh… the ramps:

PlateIVFig33_E

These would be ten feet wide and with a 1:6 slope.  Granted, if it were me those would be dressed a lot cleaner to avoid twists and turns.  Anyone who’s moved a couch into a small apartment door might relate.

Great!  We have a battery with five guns in barbette on the salient angle of the bastion. But everything has pros and cons.  So let us assess:

The advantages of the barbette consist in the commanding position given the guns, and in a very wide field of fire; on these accounts the salients are best positions for them.  Their defects are, that they expose the guns and men to the enemy’s artillery and sharpshooters.

Light guns, particularly howitzers, are the best for arming barbettes; because the hollow projectile of the latter is very formidable, both to the enemy’s columns and to his cavalry; and when his batteries are opened against the salients, the light pieces can be readily withdrawn.

See, it would be nice to have the ramps setup for easy handling.

But let’s close with focus on those advantages and disadvantages.  The barbette allowed the artillery to fire over the parapet and afforded a wide field of fire.  But unlike infantry, the artillery could not simply “duck down” behind the parapet.  And thus were exposed.  What we will look at next is an arrangement that traded field of fire for protection against enemy fire – the embrasure.

(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, pages 53-4.)

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