Amateurs study tactics, professionals study logistics”, or so the old saying goes, an admission that victory more often goes to the side which is better organised, better trained, better equipped, and more able to get more troops to the fight faster than to the side led by the supposed tactical geniuses. With few exceptions, battles are ultimately won by numbers, discipline, and morale – and those successful “Great Captains” who have been lauded as reliable battle-winners in history have often been able to secure those reputations because they benefitted from (or engineered) a system which allowed them to get a better army to the battlefield with concrete advantages which they could then exploit.
But what does all of this have to do with the size of that army?
In the first part of this two-parter, we established that societies are only able to field armies of a certain size based on the structure of their society – that the total number of troops they can deploy will be limited by their political systems, their ability to mobilise resources including money and personnel, and the state of the art when it comes to military technology – which dictates the amount of support personnel needed to maintain the combat effectiveness of the “sharp end” of any army by taking care of equipment, supply, and human needs. Now, we go from those rather general principles to talking about the specifics of field armies – which is to say, armies which are deployed as a single body into campaigns against enemy armies to pursue an operational objective.
A side-note on terminology here: “Operations”, or “The Operational Layer” is a modern term, but it’s one which has existed de-facto throughout history. It generally means the layer of war between the pursuit of a conflict’s political aims (strategy), and the nitty-gritty of how troops fight on the battlefield (tactics). The Operational Layer is what determines the movements of armies outside of, into, and out of battle. It determines where those armies can move, what objectives they are required to capture, and when those armies fight, retreat, pursue, or stand their ground. Basically, if you can think of strategy as the ultimate goal of the campaign, and tactics as the individual battles within it, operations is the sinew turning those battles into a cohesive direction. This is also the layer which concerns itself most with what we’re going to be talking about today: the process of supplying armies on campaign outside of the actual battlefield.
An army is ultimately an organisation made up of human beings with human needs and weaknesses: they need food, shelter, and water. If they don’t get these things, then they desert, or get sick, or die. Likewise, if you put too many of them together without the knowledge or ability to keep them clean, healthy, and happy, they’ll desert, get sick, and die anyway. It bears repeating that before the beginning of the 20th century, deaths by disease and infection killed far more soldiers than battlefield deaths. Even in peacetime, military units stationed in some parts of the world could lose as many as a fifth to a third of their number a year in peacetime, simply because they lacked the appropriate infrastructures of sanitation and supply.
And “infrastructure” is the correct word here. Armies are ultimately fed and equipped by systems of supply, and those systems put hard limits on the size of a particular army just as clearly as a sewer system or electricity grid might limit the size of a city – and those systems are just as similarly limited by the technology available. Everything an army needs has to be carried to it, and unless that army is either accessible by sea, or has access to railroads (or an analogous form of mass transportation), everything that carries everything the army needs also has to be fed, supplied, and organised. There are ultimately three basic ways to do this, each with its own strengths and weaknesses – and each with its own hard limits imposed on the size of the army doing it.
The first is to simply take food and supplies from the locals and make “the war feed itself”. This means that the army doesn’t need an extensive logistical system, making it the cheapest and least complex way of maintaining an army. There are, of course, obvious drawbacks. The most obvious is that it visits extreme misery on the people who are being “foraged”, as their own supplies of food and supplies are taken away from them (do not underestimate how much damage this does. Some of the most deadly events of the 20th century were caused by the confiscation of food to feed industrial or military institutions). This in turn embitters the local population against the army in question, and also causes starvation and destruction which makes that given area less able to support future foraging operations. By the end of the Thirty Years’ War, parts of Germany were so “foraged out” that armies basically disintegrated in a matter of weeks simply because they couldn’t find anything to forage.
This method also places an obvious limit on the size of the army – which can only be as big as its foraging can support. If the area being foraged is wealthy, well-developed, and flush with surplus food, then it could probably support a much larger army than one going through a barren wasteland where almost nothing grows. Likewise, this is why armies in the old days tended to operate in “campaigning seasons”, when there was enough food harvested and stored to make foraging a reliably effective way of feeding an army. Even then, it has to be remembered that before the agricultural revolution of the 18th century, even wealthy agricultural areas were lucky to have a food surplus of 15% or so – which means that the “take” from an army’s foraging operations would be limited accordingly. If an army’s foraging parties can reach across an area which can support 100 000 people, then it can probably maintain a size of 15 000 or so (total, not just soldiers, but camp followers and support personnel as well). That factor might be a little less because the locals are good at hiding their surplus food – or a little more if the foraging parties are good at extracting information and supplies through what certain individuals still refer to as “enhanced interrogation”, but unless that army keeps moving to find new sources of food to forage, then it’s not going to dramatically exceed that limit.
The second option is to rely on civilians to provide supplies voluntarily, usually by paying them for it. There’s two ways of doing this: either having the local population bring supplies to the army, or by having civilians from the army’s home territories bring up those supplies to wherever the army is campaigning. Both of these approaches have their limitations. The most obvious one is the fact that by paying for supplies instead of simply taking them, an army becomes a lot more expensive to maintain, not only in paying for those supplies themselves, but also in maintaining the staff needed to handle the necessary funds and ensure they’re going to the right people. Likewise, the suppliers themselves will often have reasons to short-sell or otherwise try and swindle the army, especially if that army is going to be long gone by the time that they find out that the supplies they’ve already paid for weren’t what was requested.
Other limitations include the fact that if an army is purchasing locally, they’re subject to the same “carrying capacity” as an army that forages, except that the latter can realistically squeeze more supplies out of the locals simply because the locals are being forced to give up all the supplies they can, not just all they can afford to part with. Likewise, an army which intends to bring up supplies from its home territories are subject to the fact that the process of bringing up those supplies themselves require supplies (as well as armed escorts if they’re going through hostile territory). The farther that army operates from its home, the longer those supply lines have to be, and as a result, the greater the proportion of the supplies being brought up are going to have to go to feeding the draught animals, sailors, and teamsters doing the carrying rather than the army at the end of the supply line.
Which is a problem that’s shared by the third method, that of using the army itself to bring up supplies from base depots in friendly territory. In theory, by subsuming the process of supplying an army within itself, that army ensures that the right supplies are going to the right places. Of course, this not only means that this army would have to devote the same sort of resources to bringing up supplies as the civilian providers normally would, but it also means that everyone involved in the process is part of the army itself – meaning that more of the resources allocated to the army as a whole are spent recruiting, training, paying, and maintaining these supply lines than would be in other cases.
Historically, armies have generally relied on the first two practises – usually the first in hostile territory, and the second in friendly territory. This means that the armies involved were strictly limited by the carrying capacity of the land they were fighting over. In a time when the fastest military unit available was mounted cavalry (and even then only for short bursts of speed without a supply of remounts), this meant that the sizes of field armies were strictly limited by the level of development of the surrounding countryside. Even in the time of the massive armies of the Napoleonic Wars, these forces were often required to march in smaller Army Corps to avoid starving to death, only reuniting when needed to fight a battle.
However, not long after Waterloo, this changed. The size of field armies not only exploded, but they also became more and more adherent to the third method, that of self-contained logistics organisations bringing up supplies from home territory.
There were two reasons for this, one leading into the other. The first was the development of the railway. Suddenly, armies were able to move vast quantities of supplies and equipment overland rapidly and efficiently. This meant that heavy equipment and ammunition – which previously had to be labouriously brought up through muscle-powered supply lines – would now be railroaded in en-masse. As maintaining an army more loaded down with heavy artillery and other advanced equipment became easier, armies began to see the development of these pieces of equipment as the primary means of securing a qualitative advantage over an enemy forces. At the same time, because a larger proportion of an army’s supply needs was made up of specialised equipment, it no longer became feasible to source much of that equipment from local populations or general civilian society. As a result of these two developments, large armies became easier to supply, and large armies using that third model of logistics became the only way to field a serious contender in the field of industrialised war.
So what does this all mean?
First of all, at the most basic level, armies are limited by the amount of food and equipment they can be supplied by. No equipment, and they can’t fight. No food, water, or (in the cases of professional armies) pay, and that army disintegrates.
Secondly, the ability to supply an army is based either directly or indirectly on technology and infrastructure. If an army is foraging from the locals, then that army is limited by the amount of population the territory within reach of that army can support. If the army is getting supplies from elsewhere, then transportation technology and the relevant infrastructure needs to be there to ensure enough supply gets to the army to keep it together.
Thirdly, unless the army is entirely living off the land, it will be smaller the further away from home it operates, as more resources need to be spent supplying each individual soldier the further they are from their base of supply. That explains why (for example), the Spanish Habsburgs struggled to maintain small armies of a few hundred or a thousand in its far-flung American colonies, while being able to maintain nearly a hundred thousand men in the Army of Flanders in the Netherlands for decades on end.
Fourthly, everything changes when mechanised mass-transit enters the picture. When an army no longer has to feed itself with a supply line which also needs feeding (or at least, not a lot of feeding), supplying an army across long land distances gets much easier.
Last of all, some hard numbers to give you some reference points: the largest individual field armies of the pre-railroad age were usually about 50 000 or so. Larger armies were possible, but they were often made up of multiple individual army corps combined together for the purpose of a single battle. These were the armies which were fielded by the highly developed military systems of very large and powerful states like the Han, the Romans, and the Achaemenids at one end, and the semi-industrialised great powers of Europe like Napoleonic France and Prussia on the other. This is more or less as big as an army gets unless it is operating very close to its home base (like the gigantic Roman army which got wiped out at Cannae, or the aforementioned Army of Flanders).
Armies raised by much more fractured, less centralised states like the kingdoms of Medieval Europe were much smaller. 20 000 men was considered a really big army (like the French at Agincourt or the Polish-Lithuanian Army at Tannenberg-Grunwald). Even an army of 5000 or so was usually a full-effort undertaking. Most feuds between powerful nobles usually only involved “armies” of a few hundred, or even a few dozen.
On the other hand, after railroads, armies massively increase in size, from tens to hundreds of thousands. During the Russo-Japanese War, the Russian army tried (and almost succeeded) in supplying something like 700 000 men through a single half-finished railway line. Eventually, you’d find forces so large that they’re able to create continuous battle lines across entire continents.
If you all want, I could probably put together a list with some more data points, to give you more of an idea of how big an army in a given time period or situation (or its equivalent) ought to be.
Or we can talk about something else next month, up to you.
Paul Wang 