Dahlgren on shrapnel (case shot): “… even a tolerable approximation … not likely to be undervalued…”

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.

I mentioned John Dahlgren as one of those looking the performance of shrapnel.  So let us turn to his 1852 “A System of Boat Armament in the United States Navy.”  Now keep in mind that work was more so a justification for the concepts incorporated in the boat howitzer system (which exceeded expectations, mind you).  So there is some carry over of that intent.  But the part we want to consider here is within the section discussion ammunition for those boat howitzers:

Within the last fifty years, another projectile, the shrapnel shell, or spherical case shot, has been contrived, partaking somewhat of the nature of the shell and the canister, and in a great measure superseding the plain shell, where troops are fairly open to its action.

Dahlgren continued on, continuing to slight the projectile class with the label of “novelty”, while discussing the evolution of shrapnel – from Napoleonic times up to the 1850s.  But this was not to say Dahlgren did not rate shrapnel of use.  He found shrapnel of value beyond the range of canister.  And he added that specifically applied to naval operations, shrapnel was useful, even within canister’s normal range, to support landing operations.

As to the use of shrapnel:

It is designed to burst the shrapnel in front of the troops exposed to it, and at just such a distance and height as to disperse the charge of balls among them.

Here the difficulty lies.  If the shrapnel burst too high, too near, or too fr, then it is alleged by the objectors that its power is lost, or so far diminished as to be trifling.

The conditions to an execution so exact are said to be: –

  1. In appreciation of the distance.
  2. In timing the explosion.
  3. In adjusting its height above the object.

When bodies are moving with velocities of several hundred feet in an instant, spaces of time which it seems ridiculous to attempt the appreciation of by ordinary means, become not only important, but very plain to the perception, by the differences in the explosion.

Yes, we see the same issues discussed in my earlier post, but yet simply related by way of illustration.  Dahlgren was picking at this problem….

The importance of knowing the distance can hardly be over estimated, and the difficulties of making even a tolerable approximation to the truth are not likely to be undervalued by artillerists.

Emphasis mine.  Given that assessment, Dahlgren approached the problem in his typical manner – starting with an analysis to define just what the problem was.  With respect to the first point, distance, he noted practices that might be employed to train crews to better determine range.  Furthermore, he pointed out the naval gunners had the advantage of seeing water thrown up by the shrapnel, an advantage over shrapnel fired over land.  And he added:

The adjustment of the fuse to the distance, and the altitude of explosion, are regulated to the elevation; and therefore, the three conditions to good effect may be said to depend mainly on a correct knowledge of the distance.

With that established, he saw the need to test….

Considerable experiment will be indispensable to determine accurately the proper regulations of elevation of gun, time of fuze, and height of explosion; and systemic practice must be resorted to afterwards in order to familiarize officers to the use, and enable them to make effective application, of the shrapnel.

Or in other words, put this down in a manual so all can be trained on the practice and the practice be made repeatable.  Yes, the brass ring of all doctrine writers!

But this was not simply an exercise in establishing range tables and providing range estimation training.  Shrapnel behaved differently than shot and shell.  And that was not necessarily a bad thing:

It is in the peculiar dissemination of its balls that the shrapnel promises some corrective for errors in the estimation of distance.  Following the course of the trajectory, with a velocity not less than that of the shrapnel at the instance of explosion, they radiate from the case in the form of a cone; and, when projected on the horizontal plane, take an elliptical figure, the greater axis of which coincides with the continuation of the trajectory, and is much elongated, particularly at the low elevations.

We might call this a “shotgun pattern” of sorts. Dahlgren called it a “jet of balls”, adding the pattern was tighter the closer one is to the point of the burst.  In order to fully understand this behavior, Dahlgren cited some test data:

Three muslin screens were stretched on upright frames over the water, fifty yards apart.  In dimensions, they were twenty feet long and ten feet high.

DahlgrenShrapnelPlate5

A frigate’s launch, carrying a 12-pounder of 750 lbs. in the bow, was placed 545 yards from the nearest screen.

Its charges were one pound.  The elevation by sight 1.3 inches.  The motion of the boat precluded the use of an instrument for this purpose.

The shrapnel (charged) averaged 11.4 lbs., containing 80 musket balls (17 to the pound), and four ounces of powder.

The fuzes were two seconds, and such as are issued to the service.

Eight rounds were fired with the following results: –

DahlgrenShrapnelTable

The gradual increase of the dispersion with the distance is exemplified by the number of balls in each screen, the mean of these eight rounds reducing the effect one-third for 50 yards, and two-thirds for 100 yards.

Dahlgren went on to work on variables which caused variations with the distance of the burst.  And he provided some insight into the behavior of ricochets.  But, while cautioning the test was a small sample size, he did offer a third party observation:

From the data above, the distances of 60 to 150 paces in front of the object (50 to 129 yards), with heights of four to fifteen feet, have given good results with cannon, apart from the ranges.

So here we have a planning figure – shrapnel should explode 50 to 129 yards in front of the target at a height of 4 to 15 feet in order to achieve the best effect, given dispersion of the balls.

As for performance of the balls on the target, Dahlgren observed:

The force of the balls was sufficient, in every instance, to pass through pine boards one inch thick, placed behind the screens, the distance of the third screen from the explosion being sometimes 150 yards.

So we add to the planning figure the effective range of shrapnel – 150 yards beyond the burst.

Dahlgren departed analysis of the test results and moved on to summarize opinions about the merits of shrapnel, which was certainly a spirited debate among military authorities of the time.  At the end he suggested a conclusion (as Dahlgren, being somewhat a “staff officer” at this time, was not the decision maker):

Is it not more judicious to improve its operation to the utmost, by thorough experiment and practice, and to look to the results of actual service for a settlement of the several issues raised; neither blindly confiding in the alleged superiority of the new projectile, nor, on the other hand, allowing its probable merit to be depreciated by a too ready skepticism?

Let us put a healthy highlight on Dahlgren’s suggestion.  On one part, we see tacit admission the behavior of shrapnel was not well documented.  On the other part, he exposes a situation we, removed from things 150 years, may not appreciate – Not all authorities, Army and Navy, were convinced shrapnel was worth the trouble.  That’s important!

However, let’s close this on the technical side.  Dahlgren determined shrapnel was most effective when bursting 50 to 130 yards (I’m rounding) in front of and 4 to 15 feet above the intended target.  That’s the factor we seek to apply to practice… or more accurately for the purposes of discussion, that is the factor we want to see evidence of being applied to instructions given to gunners.  Got it?

(Citations from John A. Dahlgren, A System of Boat Armament in the United States Navy, Philadelphia: A. Hart, 1852, pages 37-50.)

 

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One thought on “Dahlgren on shrapnel (case shot): “… even a tolerable approximation … not likely to be undervalued…”

  1. […] 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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