Guns per 1000 infantry? Or guns per 1000 yards of earthwork?

Yesterday I wrote about the reduction of the Artillery Reserve and general reorganization of the artillery arm in the Army of the Potomac from mid-May 1864.  Some historians have offered this as an example of the dominance of rifled musketry on the battlefield – that artillery could no longer move within range to be of use.  And of course with the fighting in the Overland Campaign marked by extensive use of field fortifications, this is an easy “surface” explanation to seize upon.  Indeed, this is the emergence of  “modern” warfare that so many historians have proclaimed.  But there are some finer nuances here that point less to a revolution in tactics and more to application of a different set of tactics manuals.

Up to the summer of 1863, the most applicable manual, for the division level and above, was An Elemntary Treatise on Advanced-Guard, Out-post, and Detachment Service of Troops by Dennis H. Mahan (and yes the title is much longer, but I lose patience!  So allow me to simply say “Outpost“).  In Outpost, Mahan set forward a general operational framework for the US Army.  Though it’s title suggests something more applicable to frontier service, the manual’s real focus was how a field force – be that small or large – should operate on campaign.  Mahan included sections on employing the various arms and how to arrange them for the march, employ them for combat, and general disposition.  And I’m offering just a lead-in paragraph here, as the manual does deserve deeper treatment, due to its influence upon the West Point officers in particular.  (But indulge me for the moment, as I focus on the Overland Campaign and artillery….)

For the artillery, Mahan wrote:

Its duties are to support and cover the other arms; keep the enemy from approaching too near; hold him in check when he advances; and prevent him from debouching at particular points. To perform these duties it is considered that an allowance of one piece for each thousand men of the other arms, and one in reserve forms the proper quota of this arm.  It is to be remarked, however, that this proportion supposes the other arms in an excellent state of organization and discipline.

Mahan went on to say the quota should be increased for less well trained troops.  The Field Artillery manual held to that premise, and of course William F. Barry and Henry Hunt cited those quotas when forming and reorganizing the artillery through the first half of the war.

Mahan also discussed the tactical employment of artillery noting employment guidelines:

The distance between the batteries should not be over 600 paces; so that by their fire they may cover well the ground intervening between them, and afford mutual support; the light guns being placed on the more salient points of the front, from their shorter range and greater facility of maneuvering; the heavier guns on the more retired points.

This, again, was a guideline for employing artillery, in the field, in defense.  Within the context of Outpost, this is how artillery was placed on a battlefield when coming out of a march and into an engagement – in the case of the particular passage, for defense.  On the offense, Mahan alluded to the ratio of batteries to the composition of the attacking column – a proper mix of infantry and artillery.  Notice how, even though we have a suggested interval between batteries, the employment hung on the number of troops supported.  Not the amount of line held by the troops.  And the batteries are placed where they might support one another.

Now let me switch over to another of Mahan’s “gospels” on tactics… A Treatise on Field Fortifications.”  There Mahan wrote:

In the defense of works, the pieces should be so placed as to cross their fire upon the ground over which the enemy must approach. The heaviest pieces should be placed on the most secure points, and in such positions that their fire may not incommode the troops defending the work. The light guns should be placed at the advanced points, as they can be most easily withdrawn. The howitzers should occupy points from which hollows, woods, &c., in advance of the works, can be reached by their shells.

No where does he set a ratio of guns to troops.  Instead the cannons are to be arranged in response to the terrain and likely direction of attack.  So in the field fortifications, the idea was to adjust the number of guns based on the terrain in front of the works.  From there a practical mind begins to think about the length of the line … say…  how many guns needed per thousand yards?  Granted that ratio will vary with, as Mahan dictated, the nature of the terrain.

Comparing the Chancellorsville Campaign to the Overland Campaign – which is rather convenient given the same localities, just a year apart on the calendar – I submit the changes for the artillery arm were in part a function of a change in the approach.  The Artillery Reserve represented a mass of combat power, though somewhat a cumbersome instrument to employ.  A year earlier, the tactical approach was to present overwhelming combat power at a critical point at which, the enemy would be crushed or forced to “ingloriously” flee.  On the Overland Campaign, the tactical approach was to maintain contact while maneuvering ON the enemy.

That, more than anything else in my opinion, brought on the increase in field fortifications.  And with field fortifications, artillery was allocated by measure of yards on the front as opposed to men in the formation.  That “front line” formula then had several effects on the rear area.  To the point of this post, the Army of the Potomac could then get by without an artillery park of several hundred guns.  Having just enough guns to distribute across the lines was sufficient.  And I’d conclude that change was not due to some revolution in tactics, but rather because someone had read their “Mahan” and applied it generously.

Henry Hunt will probably look down with disdain, but I think the decision to break up the Artillery Reserve and ammunition trains in May 1864 was justified.  We might even contemplate a measure of hours, if not days, its reduction saved on the march south.  But in the same breath, I would be quick to add, Hunt was indeed right – the army would need those guns and ammunition trains back in good order.

(Citations from Dennis H. Mahan, Elementary Treatise on Advanced-guard, Out-post, and Detachment Service of Troops, and the Manner of Posting and Handling Them in Presence of An Enemy, New York: John Wiley, 1861 (“New Edition”), pages 39 and 60; Mahan, A Treatise on Field Fortification, New York: John Wiley, 1852, page xxv.)