Case shot and practice of fire: A conundrum?

Consider this figure:

OwenPlate20Fig6

This particular figure appeared in “Elementary Lectures on artillery: Prepared for the use of the gentlemen cadets of the Royal Military Academy” by Captains Charles Henry Owen and Thomas Longworth Dames, published in 1861.  And as “Royal” implied, these were English officers and not Americans.  Still, the technology was the same and applied in much the same manner.  It is similar to illustrations appearing in American texts of the same period.  I simply chose this source because the basic illustration was cleaner.

Basically, this illustration explains the practice for firing shrapnel.  The target, on the far right, is a box labeled “Column of Men.”  And we see four examples where shrapnel was fired.  Only one of which was accurate and would achieve the desired result.  Labeled “a”, I’ll put a star on that point and show the respective coverage of the balls after bursting:

OwenPlate20Fig6A

The perfect shrapnel burst – at the right time of flight; at the right height; at the right angle of flight.  The momentum of the shrapnel shell (case shot… for us not subject to His Majesty) imparted forward progress to the balls after the burst.  So we see the expected pattern would place fragments and balls across the formation of infantry.

If the the fuse was set for too short a time of flight, then the shrapnel burst too soon.  At this case, point “b”:

OwenPlate20Fig6B

The payload falls well “short” of the target. Not to mention, and not depicted here, it was also possible for the burst to be “long”, with the payload landing well beyond the target.  So setting the fuse

But the fuse timing was just one of :

OwenPlate20Fig6C

Or if the projectile is fired too low:

OwenPlate20Fig6D

This brought the burst too low and well in front of the target.

Not illustrated in this figure is the angle of flight.  But you might get a feel for that looking at bursts “c” and “d”.  However, as case shot/shrapnel was fired primarily from guns, sometimes howitzers, and not mortar.  So this was somewhat a “goes without saying” consideration.

Still we see depicted two of the three necessary components of a proper shrapnel burst.  The right height being the darkest of the three trajectories depicted.  We see points “a”, “c”, and “d” being the right time of flight.  Allow me to “box” these to highlight:

OwenPlate20Fig6X

Hopefully nothing entirely new to artillery enthusiasts.  Just depicting the desired work of the shrapnel… er… case shot… in combat.  As we well know, the artillerist would need estimate the range to target.  From that, he would derive the necessary elevation.  That, of course, considering the desired height of burst.  And the artillerist would need to calculate time of flight to the optimum bursting point.  That being used to properly cut or set the fuse.   And…. goes without saying the artillerist would also need to point the gun toward the target (a factor not easily depicted in the two-dimensional world of the illustration).

Great!  So the artillerist had to do a lot of computations in the heat of combat.  One might think the manuals would have a lot of tables and guides as to how one should compute bursting height and time of flight.

Given such complications, one might think that manuals of the period would devote much space to instructions.  Well…. The brand new “Field Artillery Tactics” of 1861, from the minds of William French, William Barry, and Henry Hunt, mostly covered how to maneuver the battery.  Though unofficial, John Gibbon’s “Artillerists Manual“, with a wealth of insight for the gunners to consider.  Yet it also lacks any details on the practice of firing case shot.  Even Owen and Dames, from which these illustrations are taken, did not discuss the practice in any length.  They felt an illustration would suffice, apparently.

These references would offer elevations, range, and, perhaps but not always, time of flight for selected weapons.  But none would offer details of the ballistic behavior for shrapnel at the point of the burst.   Such was not simply derived by extending the trajectory out to the ground.  Rather one had to consider loss of momentum of those balls, fragments, and sub-projectiles, which fell off at a greater rate than a complete projectile.  And I’m just scratching the surface of the data needed for one to compute a “good” firing of case shot.

There are very few recorded experiments conducted at the time to learn how case shot behaved (Dahlgren’s experiments for boat howitzers come to mind, but there were some US Army and British experiments in this regard).  Yet, very little of what was learned went into the manuals.

That, I would submit, is a conundrum.

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7 thoughts on “Case shot and practice of fire: A conundrum?

  1. Sir,
    I’m wondering if perhaps it’s not quite so complicated. As Lt. William Broun states in ‘Notes on Artillery’ Richmond, 1862 – “…the gunner guesses at nothing but the distance of the object. The time and elevation corresponding to each distance are recorded on his scale ready to hand, and it is only concerning the distance about which he is called upon to form a judgement.”

    My reading of period gunnery is that the piece is pointed and elevated just as prescribed in the tables of fire, then for case the fuse is timed forward of the target by 50 to 75 yards. I don’t believe he needs to do any extra calculations – just estimate on the target and set the fuse for 75 yards shorter. I had assumed that fused distance ahead of the target also served to keep the round 20-50 feet overhead as it’s plunging. As the bursting charge is only enough to crack open the ball thereby expanding the shrapnel without altering velocity (unlike a shell), it seems your strike area isn’t going to vary much from where it would have fallen if the round had not detonated, just in a wide cone.

    Of course the gunner will also always step to the side to “best observe the effect of his shot” and alter his estimations of distance as needed.

    Thank you, I very much enjoy reading all of your posts!

    • All sounds good. But let’s start with “set the fuse for 75 yards shorter.” How do you translate that into the place to punch the Bormann fuse? That bit of information is not shared by Gibbon, Hunt, Barry, etc. in the manuals. And keep in mind that “75 yards of projectile flight” at the muzzle is a fair bit longer than at range. So there’s a fair bit of ballistics that should be figured out beforehand.

      And the other bit to keep in mind is the height of the burst. The optimum height would be determined by the size of the target. Perhaps… Or perhaps one would simply say a 50 foot height would suffice for a generic target. OK, but now the artillerist need to do more figuring to ensure his case would reach the desired 50 foot height, at a time (figured by the above calculations). So lets say the target is at 700 yards. Does any artillery manual of the period provide us with the elevation needed to place a 12-pdr Napoleon round 50 feet above the ground at 625 yards? None. The figures are range at a particular elevation to first strike (and in some tables ricochets for solid shot).

      And…. when the rifled projectiles came into use, case shot ballistics were even further complicated.

      Lastly, Dahlgren and others who experimented with case shot did report significant differences in the flight patterns of case shot vs. standard shells. So we are back to the same question – why did none of this work into the manuals?

      I agree with you (as was going to be my next observation on this theme) that in practice the gunners would simply observe effects and alter elevation and fuse settings accordingly. That does make sense. But that is off the target which I’m directing us to contemplate here.

      Why was there little information shared, in the manuals and other contemporary sources, about the performance of case shot? And what does that tell us about those defining the practice of gunnery?

    • Jeff, still nothing… absolutely nothing … in the form of a time of fire for case shot. Nothing. Case shot, weighing differently than standard shell, would have different ballistic properties.

      As for extra calculations, again refer to the diagram in this post. There WAS a need to determine the proper bursting height in order for shrapnel/case to work as required. At 500 yard range, that height might be 30 feet. At 1000 yards range, that height might be 75 feet. And for 6-pdr, with a lower arch of flight, that figure would be significantly different than with a 12-pdr Napoleon (not to mention a 12-pdr howitzer). I’m not trying to be nit-picky, rather just citing the sources (in this case the illustrations we see used throughout the period). They identified the behavior as “short” and “long”… and therefore we must acknowledge the gunners would be schooled in how to prevent such. So where is that in the school of the gunner?

      Finally, let me again say there WAS a difference in the fall of shot, fall of shell (prior to ignition of contents), and fall of burst shrapnel. What is interesting is that Dahlgren and others noted this prior to the Civil War, yet even in 1916 the artillerists were still grappling with such details.

  2. I believe the tables of fire have already taken into account that “fair bit of ballistics that should be figured out beforehand”. I note on the Napoleon table for spherical case that the round travels 300 yards in the first second, but only 175 yards between the 4th and 5th second of flight.

    Using your example of sending a shrapnel round from a Napoleon to a target at 700 yards – On the table of fire it looks like at 2°elevation the flight time would be 3 seconds out to an impact 730 yards distant. So now if we point on target at 2° and set our fuse to 2.5 seconds (listed in the table at 635 yards out) wouldn’t our plunging round be at roughly the correct height when it explodes? From ‘On the Use of Field Artillery on Service’, by Captain Taubert, Prussian Artillery, as translated by Lt. H Maxwell, Bengal Artillery, London 1856: “The height of the explosion is the perpendicular distance of the point of explosion above the ground; it should be so high that the projectile would strike the object as a round shot if it did not explode”.

    As to the point of observing every shot – Taubert also states “never estimate the distance at too high a figure, but rather somewhat under the mark, and carefully to observe the point of explosion of the projectile, in order to acquire a datum for the determination of the correct distance by the exact time of burning of the fuse”.

    Yes, to your original point, it’s still a bit of horseshoes and hand grenades, but as stated in the manuals, we are using case against “masses of troops”.

    The Taubert work has a comprehensive chapter on “Value of Shrapnel Fire of Guns” that I believe you will find to be extremely relevant to your conundrum. I have not been able to find an equally thorough period American treatise on the subject, but I’ll look around a bit more.

    Thank you for the discourse, I wish I’d payed more attention in my math classes.

  3. […] As I’ve opened the ball here, I feel bound to continue the discussion about the practice of case shot… and in particular how this was related to those training to man the guns.  Let me say again for emphasis – the conundrum here is that very little is offered in the manuals (US manuals, but if we want that extends across to the British manuals of the period), yet the type of projectile was seen as a vital component in the ammunition boxes. Specifically, we do not see specific instructions, firing tables, or other such details offered in the texts available to new artillery officers.  I would contend in the context of 1861, with hundreds of volunteer officers grasping guidons as brand-new battery commanders, what was in those manuals was of extreme importance.  And all this in light of experiments and tests in which some very good minds determined shrapnel / case shot should not be handled simply as any old shell. […]

  4. […] As discussed earlier, while working on a system of boat howitzers to equip the US Navy, John Dahlgren conducted a detailed study of the behavior of shrapnel.  He identified three factors which governed the performance of shrapnel, from a target point of view, and thus would provide the requirements for the practice of fire for such projectiles.  Those were the range, the time of projectile flight, and height of burst above the ground. And those were the same requirements we saw in the illustration from other pre-war manuals. […]

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