Gettysburg, Day 4: Horsepower, Hay, and the Limits of Logistics

In the previous post, we established the notion that an artillery battery’s combat power is directly related to the ammunition on hand, and can, theoretically, be expressed in hours and minutes of “staying power” in battery engaged in battle. But such quantifies but one (the last one) of the three questions posed with logistics. What of the resources expended to move supplies and the time involved?

Again, working backwards on the questions, we next have to consider the requirements for moving a chest of ammunition. A chest for a 12-pdr Napoleon weighed, by the book, 484 pounds. Let’s round that up to 500 pounds… because … well you know, round numbers. But 500 pounds is significant for another reason. In a word, horsepower. Allow me to steal this illustration for Wikipedia:

I’m not going down into the story of James Watt here, but just know there is an interesting history, steeped in 18th and 19th century technology, that brought us to the measure we know today as horsepower. Suffice to say, one horsepower is the ability to lift 550 pounds. But we need to translate “lift” to “pull” here. The Army’s manuals indicated a healthy horse could pull between 600 and 650 pounds, in addition to its own weight.

I’ll try to keep the math simple, with no decimal places or fractions to fiddle with. At 500 pounds (484 to be exact), we see the need to have one horse in order to move one ammunition chest. And we can’t split horses into parts, so it is a one-for-one allocation. And we are going to need that spare horsepower anyway, because in addition to the weight of the chest, one has to factor in the “overhead” of the vehicle used. If we want to move three chests as part of a caisson, we’d need six horses to pull 3,811 pounds. I think those numbers were chased down in a posting from many years back, if you want to check those figures. Even putting four chests on a standard wagon will require at least four horses. Not to mention extra manpower expenditure transferring chests from wagon to caisson.

The great thing we have with this figuring is a clean discussion of how many “resources” are required per unit of supply. Um… not so fast… the teamster says. Those horses must eat. A good rule of thumb is that a moderately active horse will eat between 1-2% of its body weight per day. A heavily worked horse increases that up to 3%. During the Civil War, the army sought out healthy horses between 1100 and 1200 pounds. So a well worked horse in our “one chest equals one horse” equation would need between 24 and 36 pounds of food per day. I would actually go with 25 pounds as a practical guide here – not over-feeding the horse, while keeping it healthy.

The Cheetos munching crowd will say, “horses eat grass, problem solved, right?” Nope. Not by a long sight. First off, horses have diets. They eat some grasses, sure. But not all grasses are equal in nutritional value. Nor are all grasses healthy for the horse. For an army on the move, there might not be a lot of fields left for grazing. Better to bring 25 pounds of sustenance for the horse, just to be sure. Likely that is a mix of hay and grains. So you see we have more overhead to factor. At the same time, we see yet another planning equation emerging – 25 pounds of hay provides one ammunition chest.

The other problem with “just let them graze” is the nature of the horses’ digestive system. Gluttony is bad for horses (as it is with humans… but you know). If left to its own, a horse will eat in small increments. We call that grazing, of course. For normal healthy grazing, the animal’s keeper would need to allocate several hours per day. Even if not out in the field grazing, a good teamster would not simply dump thirty pounds of hay out there for his horse to consume in one go. Small increments, spread out over the day. Bottom line, unless you want horses who cannot pull the required 500 pounds plus of payload, you better feed them well and in the proper manner.

That means the logistician has another set of measures to consider – one horse will need four to six hours per day for meals, if kept healthy, not rushed. Wow! That really cuts into the work day. Good news, horses only need four or five hours of sleep. Still, we see another governing factor in play here, as keeping the horse on healthy habits means only getting at most 16 hours of work out of the animal.

I know… there’s a war on and we can’t have all the luxury letting these horses munch and sleep in… well, I hear you. And that’s one of the reasons why the Civil War was so destructive on the horse population. The logistician who didn’t make allowances for those healthy practices would soon find another problem square in the face – finding more horses to replace the worn out and dead animals.

Still, we go back to the measure of sixteen hours of horse-work per day. A horse can pull a wagonload between 10 and 15 miles per hour. Factor that into the equation. One horse hauling one ammunition chest for sixteen hours can be expected to cover 160 and 240 miles. For planning purposes, we narrow that down to 180 miles as a good day figure. There are a lot of additional considerations of course, as supply wagons rarely operated singly. And convoys tend to operate at much slower speeds than the normal cruising rate of any vehicle. The figure of 60 to 80 miles is more accurate, historically. Indeed, that fits with known supply train movement rates in the Gettysburg campaign (specifically those dispatched by the Federals).

So now we have some rough numbers to throw around in regard to the first two questions. On the Federal side, the main supply depot is in Washington, D.C., some 85 miles give or take. One day’s work for a horse pulling a wagon in a convoy. Horses, of course, were allocated as part of teams. Given a four horse team, a supply wagon could haul four ammunition chests on that trip, with sufficient payload to spare for food for the horses in the team (preferably so as to not impose that overhead on additional teams, but we know that was not always possible). In that march, the wagon team gets 3.4 miles per pound of horse fodder. Those four chests of ammunition could keep a Napoleon gun on the battlefield at the preferred slow, deliberate rate of fire for four hours.

Circle back to the earlier post when we determined a gun’s four chest allocation would allow it to remain in action, at the slow, deliberate rate, for four hours. It takes one day to move those four ammunition chests up from the depot in Washington. The horses pulling that wagon on which those chests are carried each require 25 pounds of hay. So by rough estimations, the cost of keeping one gun in action for one hour at the slow, deliberate rate is 6.25 pounds of hay.

That’s for one gun. The Federals had 372 guns in the Army of the Potomac. Maybe not all at Gettysburg. But you get the picture. Now I’m not going to say the Federals would be firing every gun at a constant rate of a round every couple minute for every hour of the battle. Rather to say that each gun had about four hours worth of “shooting time” from its allocation of “valued rounds.” And the minutes within those hours would be husbanded accordingly.

Of course, we know that Henry Hunt had a wonderful, yet unauthorized, ammunition train supplementing that allocated to the batteries. That came into play on July 3, allowing the Federals to sustain “shooting time” for its guns despite being heavily engaged for the previous 48 hours, in some cases. But at some point even that was going to be depleted. The good logistical plan would have a complete replenishment each day. If not, there would be limits as to how much combat power could be projected from the batteries. If the situation limited how much the cannon could “speak” then infantry or cavalry movements would likewise be governed.

And we have yet to speak once here of how many crates of .58-caliber ball ammunition was needed for the infantry. Whole different set of equations in order to figure the “shooting time” for an infantryman working out of his cartridge box. Likewise, figure on the pounds of hardtack or other food stuffs needed to feed the soldiers. There are planning factors and equations that one cold derive there too. Oh, and don’t forget that every horse pulling guns or serving as a mount for the cavalry troopers will need the same 25 pounds or so of food per day. All of this is adding up to more and more supply wagons needing to make that one day trip out from the depot in order to just sustain the combat power in the field.

Criticism at the time, and certainly in the century that has followed the battle, has at times faulted Meade for not aggressively pursuing the Army of Northern Virginia starting on July 4, 1863. I think that criticism is often made without thought to the logistical situation that Meade faced. When we quantify the situation in terms of numbers of wagons needed to keep the Army of the Potomac in the fight, per day – indeed perhaps down to the pounds of hay required just to move the needed supplies – there is something to be said for Meade’s hesitation.

Gettysburg, Day 3: Cannon Shells and Logistics

Preface: Sorry this is posted a day late. Intended for this to go live yesterday, but was too busy with other matters. Readers, hopefully, will understand… and enjoy the refinement that an additional day of rumination brings.

We hear this quip a lot: Military professionals study logistics! And as my theme in this Gettysburg series of late has been aimed at the importance of staff activities in relation to the battlefield, only natural that we should shift from intelligence and reconnaissance to logistics.

If I may again send a jab at the armchair general ranks here, everyone will agree logistics is an important facet to military operations, but so few really grasp the nature of logistics as a discipline within the science of military operations. That’s because we are a lazy lot. Logistics requires a grasp of details. One really has to dive into the numbers in order to understand the nature of logistics. It’s a whole lot of “left brain” stuff. More so than the average attention span is apt to allow depicted in… say… a movie… or even a blog post. But we will give it a swag here.

We often see logistics depicted in wargames as if a tether restraining a unit to its base of supply. In the Avalon-Hill-type games, often the rules (and optional rules at that!) specify the need for a unit to trace hexes back to a road, and thence back to a point of supply. And that might be the unit’s headquarters, a dedicated supply chit sitting on the map, or a hex location presumed to be a big pile of stuff. Regardless of the particulars, the rule presumes logistics is simply a flow of things which is regulated by distance more so than the resources involved. True, distances are an important regulator when discussing logistics. But that’s not the only regulator, nor is it the most important.

To study logistics, one has to understand and eventually master a vast set of formulas. If not precise algebraic formulas, not something far off that. But at the base, there are three basic foundations to any logistical problem:

  • How long will it take to get the needed resource (supply) from source point to issue point?
  • What resources are expended in order to get the needed resource (supply) across the gap from source to issue?
  • What is the value for the gaining unit with the issue of that resource (supply)?

I don’t mean to make this sound all Mahan-ish on you. But these are the basic measurements we have to somehow quantify in order to really understand the logistics. I’m not going to say this is the only way to quantify logistics. Just saying this is one approach, easy for those without a great deal of direct experience to grasp… and one we might directly apply to Civil War situations.

So… we need to know the time taken to move the supplies, as that will determine the lead time… or on the need end of the logistics, the wait time. We need to know how much the movement of the supplies will cost in terms of man hours, wear vehicle, gallons of fuel… or is that pounds of hay…, and any other resource allocation which is needed just to move the “stuff.” And the top end determining factor is what will the force receiving the supply be able to do once in possession of that supply which they cannot do without.

Very important point that last one. Nothing worse than opening a box of fancy hats at the moment one most needs bullets

More to the point, if you narrow down the military science to the measure of how much “combat influence” or “combat power” has unit has on the battlefield, then we are talking about things like the number of bullets per man that unit has. We logically move to a discussion of how long that unit can expect to engage in combat with the bullets on hand, given an average rate of fire. That then translates to a “value” of every box of bullets sent from the depot, which if we are bold in the calculus might translate to the number of minutes a unit can stand in a fight. And we can also determine how frequently those boxes should arrive.

We might argue for the infantry and cavalry some combat power remains even after the cartridge boxes are empty. Cold steel is bold, often dangerous alternative to hot lead. And for the artillerists, edged weapons are rarely an option.

Because this is “To the Sound of the Guns” and also because day three of Gettysburg features that great cannon duel, let us think about this in terms of artillery projectiles. Working backwards in the questions, as that allows us to progress from a firm footing for even those with a passing acquaintance with the battle, what is the unit of measure for cannon ammunition? Practically speaking it is this:

Taking a 12-pdr Napoleon, as in the illustration, there were 32 rounds in each chest. But remember not all rounds are equal – A dozen shot; a dozen case; four shells; and four canister. Each type with a different purpose. Indeed, let us set aside the four canister right from the start, as those were only for use at close range and, docturnally speaking, mostly for self defense. The combat power of the gun was derived from placing shot, case, and shell on a distant target. So lets trim that to 28 projectiles.. or 28 shots to be fired out of each chest.

Under a standard allowance, each cannon had four such chests – one on the limber, three with the caisson. So a total of 112 “value” rounds per gun, under the standard allocation of ammunition. Yes, keep in mind that is the “by the book” numbers. We know things were not so tidy in wartime situations (and if you didn’t know that, well… see all those numerous posts under the heading of “Summary Statements” here on the blog). But I contend those are good numbers on which to base a discussion.

Can we translate 112 rounds into the number of minutes a battery can be engaged before running out of ammunition? Yes, but we have to accept some complexities here. Obviously, if the intended target is enemy artillery (counter-battery fire which was the focus both ways on the afternoon of July 3) then solid shot might be more preferable, though case and shell had their place. Likewise, against infantry case was more applicable, though shot and shell had effects. Those preferences noted and considered, let’s keep the equation to a high level and go with 112 rounds… but reserve this line of thought for injection into the tactical situation at Gettysburg in a moment.

A really motivated crew might fire as much as two rounds a minute, but that’s not a practical rate. Brigadier-General Henry Hunt and other good artillerists are known to encourage slow and deliberate fires. And often we see that expressed as one round every two minutes. Some will cite higher rates sustained during the “hell on earth” minutes, such as occurred on the afternoon of July 3, 1863. No argument here. But I would simply point out the higher rate of fire usually translated to less accuracy, and thus a higher number of rounds expended to achieve the same tactical purpose, or worse leading to the failure to achieve the desired tactical purpose… as we shall see from the experience on the field that day.

So if fully stocked, by the book, a Napoleon gun could stand in battery firing one round every two minutes for almost four hours before needing some resupply. If doubled up to one round a minute, that’s at best a couple hours. Still we have a rough measure of one chest providing one hour of one gun’s worth of “combat power” of a crew firing “calmly and coolly.” Just a rule of thumb… not an exact measure by any means. If we change that to “frantic” fire, then one chest equals… maybe… thirty minutes.

Change the numbers a bit for a 3-inch Ordnance Rifle or 10-pdr Parrott. Those weapons had 50 rounds per chest. Subtracting back the canister again, just 46 “value” rounds (and remember that most of these light rifled guns did not have solid bolts issued at this time of the war – usually just case, shell, and canister). Thus translating to six hours of “time in battery.” At first this seems like a quantitative game changer in favor of the rifle. But as with all things logistical, gotta look at the details. A 12-pdr smoothbore shell and a 3-inch Hotchkiss weighed nearly the same (a little over 9 pounds). But the allocation of payload is different. Smoothbore shells were cavernous compared to the interior of rifled projectiles, and thus carried more “stuff” to the intended target. If we really want to “true up” this logistical measure, we’d have to gauge things like the number of balls in each case shot, by weapon caliber. Or perhaps the weight of the bursting charge in each type of shell. But for this lesson, at the 101 level, we save that for the advanced classes.

Now consider what we have discussed as would be applied to the situation on July 3. The Confederate gunners were attempting to suppress Federal firepower (artillery and infantry) lodged on Cemetery Ridge. The type of projectiles favored for that work were shells. Shot might help, but required very precise placement for effect. Case, designed to scatter sub-projectiles over a wide area, would have an effect. But it’s advantages were negated due to the limited depth of the target area. Shells, on the other hand, could have fuses cut to impart effects on a specific part of the defensive line. Thus, for Colonel E. P. Alexander the discussion is not about “value rounds” to derive combat power, but rather “preferred rounds” to achieve the desired effect from applying that combat power. Due to the tactical situation and fire effect preferences, he had but 16 “preferred rounds” per 12-pdr Napoleon and likely around 24 per Parrott or 3-inch rifle. Such limited his part of the duel from the “value round” figure of four hours down to only thirty to forty minutes of “preferred rounds.” Sure, he could (and there is some anecdotal evidence this was done) stockpile more shells in anticipation of the bombardment. But that would only correct the supply needs in the short term. And would have the additional effect of disrupting the normality of the issue of ammunition… by the regulation chest.

On the other side of the field, Hunt had a different set of criteria facing his logistic calculation. The initial targets were, just as his Confederate counterparts, enemy cannon. And again the shell was preferred for the work to be done. But Hunt also had to consider what the bombardment was designed to setup. The infantry were coming across that field eventually. And if the cannon were to blunt that attack, the guns would need ample case shot handy to apply in short order. Thus the order to conserve fire after the initial response to the Confederate fires. Instead of expending the less preferential case-shot in an attempt to disrupt, if not drive off, the Confederate gunners, better to save those four dozen rounds per gun anticipating a time when those would be of more practical use.

Keep in mind the numbers and this rough equation of combat power – specifically the time that combat power could be applied – was not lost on the rank and file. At least one battery on Cemetery Hill recognized the number of rounds left in their chests directly translated to the length of time they would be held in position under enemy fire. And they emptied chests in a less than soldierly manner… just leaving rounds on the ground. One officer later counted 48 rounds of 3-inch rounds laying on the ground where a limber had previously sat. Clearly the crew had run some numbers of their own and determined a better way to weather the storm.

We are getting rather far along here, as things will evolve. Yet still have not gotten to the other two questions. Let’s digest the matter offered thus far, and resume in the next post. The key point to keep in mind is the combat power of an artillery battery is in direct proportion to the number of ammunition chests in possession. Numbers… and type of projectile.. matter.