So some background so that you’re caught up:

In the world that I’m working on now, in 2005, the deadliest plague in history struck the world. The Black Flu as it was called caused havoc and destruction across all six inhabited continents, killing over 5 billion people by the time the Black Flu burned itself out in 2010.

Anyway, on the East Coast, the skeletal remains of the United States Government under the leadership of President Barack Obama exit Mount Weather and return to Washington, DC where they clean up the District of Columbia and through the hard work and effort of everyone, DC became one of, if not the, most fortified and powerful areas in all of North America.

When Obama was cleaning up the area, Obama made drastic changes to the scattered and tattered US military. Obama decided to disband the old US military and restructure it as a new single, unified force call the United States Garrison due to overlapping and redundant operations as well as pride being needed to be restored in the military.

Anyway, onto the question; how big should I make the US Garrison?

So far, in the current year of my world (2025), the District of Columbia (which has expanded its borders to the surrounding counties) has a population of 450,000 citizens. I was and still am playing around with numbers and I’ve decided to make the US Garrison 75,000 Troopers-strong, or about 16.5% of the DC population. The Garrison is a professional active duty military and was created with the idea of creating both a military force that will fight the enemies of the United States while also preserving internal security by acting as gendarmerie force within DC. The Garrison has to contend with fighting against bandits and marauders but they also have to deal with larger rivals that either don’t exactly like the US Government and/or want to become a part of the United States once again. The largest rival to DC is the Virginia Federation, which is based in Richmond and has 390,000 people.

I’m curious, is this too big of a military force? Please keep in mind that this is under post-apocalyptic conditions kind of like The Last Ship and TC’s The Division. How would post-apocalyptic conditions change things up?

  • $\begingroup$ What types of threats is your military dealing with? Are there post-apocalyptic "mutants", zombies, or other creatures or is the army primarily for ensuring stability against bandits and other bands of ne'er-do-wellers $\endgroup$
    – Dragongeek
    Jan 21, 2020 at 10:52
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    $\begingroup$ 16.5% of the population is absurdly high in almost any situation. Even at the height of WWII Germany never got anywhere close to that. $\endgroup$
    – quarague
    Jan 21, 2020 at 10:53
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    $\begingroup$ An Army is a bit of a luxury product, try to state what the external or internal threats are so that people can better answer the question. if it's a few 100 rednecks with low equipment then such an army would be overkill. If it's thousands of giant mutant warriors with laser guns then i would even be willing to up that number to 25%. $\endgroup$
    – A.bakker
    Jan 21, 2020 at 10:59
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    $\begingroup$ Hmmm... 16.5% of the population. The army is mostly men in any rational state, so let's say 30% of the men. Men of military age are about half of the total men, so that's 60% of the men of military age. More than one man in two between 16 and 50 years of age is in the army. You may quickly find out that you have a severe shortage of plumbers, sanitation workers, electricians, welders, mechanics, and so on and so on... Normally a rational country has something like 2% of its population in the military, tops; the Roman Empire had less than 0.5% percent of the population in the army. $\endgroup$
    – AlexP
    Jan 21, 2020 at 12:33
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    $\begingroup$ I'm surprised Obama would have come all the way from Chicago to DC in post apocalyptic 2009. Probably the citizenry of DC would have elected Marion Barry president. $\endgroup$
    – Willk
    Jan 22, 2020 at 1:48

6 Answers 6


Depending on what the threats are the numbers will change so try updating your question with some more information about it. But to give a bit of a ball park that would be realistic if you ask me.

  • No real threats, just a police force ~1%

  • Some military for exploration in possible hostile territory 1.5%

  • Confirmed hostiles in the area but no real war 2.5%

  • Cold war status with a nearly equal enemy 5% (This is the point you
    start recruiting less then ideal candidates)

  • Ongoing war 10% (This is the point where non-essential jobs disappear in to the draft)
  • It's fight or die against an enemy that shows no mercy 20%+

Reason is why this percentage is low is because you still need a dedicated workforce to supply your troops with food and arms, you got logistics staff, people to young or old to fight, people who due to a disability are unable to fight and of course draft dodgers.

  • $\begingroup$ It would be a good thing to provide also absolute numbers for the original question (by multiplying by 400K ): 4 000, 6000, 10 000, etc. For clarity. $\endgroup$
    – ksbes
    Jan 21, 2020 at 12:59
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    $\begingroup$ @ksbes i used Percentages because the original poster also mentioned them. Plus, if he decides to change the number of his survivors it would be better for him to be able to do the formula instead of having only the answers. But that's just my opinion :3 $\endgroup$
    – A.bakker
    Jan 21, 2020 at 13:53
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    $\begingroup$ I think you need to divide all your percentages by about 5 to get realistic numbers. Using en.wikipedia.org/wiki/… as a source. Japan, Germany, UK 0.2-0.25%, US 0.4%, Syria 0.7%, Israel 2%. US in cold war times was more like 1% instead of 5%. $\endgroup$
    – quarague
    Jan 22, 2020 at 11:56
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    $\begingroup$ @quarague Well his story is set in a post apocalyptic setting. This would (probably) result in over militarization based on the fact that their lack of knowledge of the world would be freighting (As in what if Russia managed to prevail with a massive force but they have no way of knowing for sure). Also this scenario would require a somewhat military dictatorship until the situation has been dealt with(A new society isnt created in a day) which further increases the numbers. And at last it will also function as security and police in his scenario something that would also increase the numbers. $\endgroup$
    – A.bakker
    Jan 22, 2020 at 12:13
  • $\begingroup$ I like these numbers the best. If you really want to stick with the 16.5%, use these numbers for Active Duty, but have the difference be Reservists. Also, one of the major missions of the US Military is in civilian support (construction, disaster relief, etc) $\endgroup$
    – Starshine
    Jan 22, 2020 at 22:54

As is so often the case, you should ask yourself what problem you want to solve. Having an army is an expensive and also a dangerous hobby.
It means having a large group of well-educated and armed people, that sit around doing nothing while still needing to be fed, clothed and equipped.
You have a post-apocalyptic setup, and all of the population of a medium-sized city. What do you need an army for? which enemy are they supposed to fight, or scare off? and why is it more viable to feed a standing army than coming to terms with your neighbours, and what neighbours are there?

So long as these questions are not answewd, the question about the size of your army is meaningless.

  • 4
    $\begingroup$ While I fully agree, this is more a comment than an answer $\endgroup$
    – Rekesoft
    Jan 21, 2020 at 12:44

I hate to write this kind of answer, but you're taking this the wrong way round.

Forget population for a moment: exactly where does DC rule? You suggest neighboring counties. OK, let's start with Fairfax and Arlington in Virginia, and Prince George's, Anne Arundel, Calvert, Montgomery, Howard and Charles in Maryland. This gives a fairly compact area bounded on the east by the Chesapeake Bay, relatively easily defended and providing access to what's left of the Navy. Total area is 3,237 square miles. Pre-Plague population was 4.5 million. Average population density is now 140/square mile.

You've got a problem: how do they feed themselves? This whole area is heavily built-up, since it's essentially a suburb of DC. And the first places that are built on are flat, which means farmland. Ex-farmland. Oh sure, there's plenty of government buildings to house the government, but that's not very useful, since there doesn't seem to be a unified country to pay taxes. Nor is there much in the way of local manufacturing, nor mining, nor power generation.

That last is important. Without electrical power, DC is a swampy pesthole. There are presumably no surviving transmission lines - at the least, any dissident communities will take them down. Plus, of course, DC has no way to pay for power. Ditto for oil pipelines. Nor is there any hydro. There are no active nuclear power plants within this area, and nukes seem unlikely to survive the apocalypse.

You might have DC become a trading city, using its access to the Chesapeake to access the oceans, but you need to think about that pretty carefully as well.

So, what else? You could think about expanding to the west. Let's say, Loudon, Fauquier, Prince William, Stafford and King George counties. That's another 1960 square miles, with a good deal of farmland. It also has the advantage of being mostly bordered on the west by the Rappahanoc, Shenandoah and Potomac rivers for defensiblity. And it brings population density down to about 86/square mile, which seems like a good idea in light of:

Now. How are you going to farm this land? Mechanized agriculture? Sure, you'll need that in order to free up 1/3 of your male population for soldiering. Where will you get the fuel? Where will you build the tractors? There's not a lot of large-scale farming in that area at present. Animal power? Well, first, the Apocalypse is going to be hard on large farm animal populations, since they are great big slabs of meat on the hoof if there are starving refugees, and a lot of farmers are going to die, leaving their animals to their own devices. How will the draft animal populations (which aren't very large to begin with) survive to plow the fields?

How, exactly, do you plan to clothe your citizens? Wool doesn't do well in the South, synthetics are out. How about cotton? As in cotton plantations? You really want to go there? Trade will help, but you're still stuck with the question of what the area would have to export.

So, until you start paying attention to exactly what Washington DC is, how it functions and how it survives, planning the size of its military is very, very premature.

  • $\begingroup$ You brought up a lot of good points. Do keep in mind that I literally started this idea a day ago. But with that said, how would you address the problems that you’ve pointed out? $\endgroup$
    – user69268
    Jan 22, 2020 at 0:40
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    $\begingroup$ @user69268 - Well, sorry to be a spoilsport, but I wouldn't. I suspect that the Plague would kill food distribution, and the cities would empty out into the farm areas, with attendant social breakdown. If that doesn't happen, it can only be because the country DID stick together. Agriculture is too far removed from the population centers to get food to the cities unless the whole political/economic framework hangs together. Likewise with power. Fragmentation is likely to trigger a catastrophic landslide of disaster. Just my opinion. $\endgroup$ Jan 22, 2020 at 18:25

75,000 troopers is plausible, but unlikely

As with all things, someone on the internet has done some research on this already.

John Savage talks about this in the context of a fantasy/medieval nation, but his work should give us a good first guess.

You have a population of 450,000 citizens. Our first pass is to remove people who are not eligible due to age, critical professions, etc.

We'll use Mr Savage's numbers for this, so, we can assume about 20.8% of your population are too young to fight, 6.3% are too old, 10.4% are physically incapable, 1.4% are exempt due to critical professions and 1.3% dodge the draft.

If we assume President Obama does not ban women from the military, we get a draft pool of 269,100 people.

Of these, up to 50% could have dropped out due to "Non-chronic Disease". He's not specific as to what these could be, but if your world has just come out of an extinction level plague, I think we can count people who are still sick under this section, leaving us with about 134,500.

The final section groups up all the different roles your soldiers may be performing, from town watch and garrisons to bodyguards, plus general logistical restrictions due to a lack of transport, into a bulk penalty of 80%. This will give you your final total of 27,000 soldiers.

This seems like a good upper end, as it considers the amount you could get if you devoted every single able body to the war effort (possible, if your military campaign occurs during the labour-light period of the summer between sowing and harvest, or occurs just after harvest and before winter set in. It also only considers the number of soldiers you have available for a military campaign. If you wanted to leave your lands under defended and under policed, you can get reclaim half the soldiers lost to the final stage, giving you about 80,000.

This still has its issues however. If you're equipping everyone with spears and shields, the essentials to fight in a battle can be taught in a week or two. But if you're giving everyone firearms, they will need more training.

Thus, if you have a militant society with plenty of guns and ammo to practice in their own time, you could achieve a campaign army 15% the size of your nation

But, if you ban one gender from combat, and can't afford to take garrisons and police away from their posts, your army will likely only be 1.5% the size of your nation, instead of 15%. In addition, your "Non-chronic illness" section may not be up to 50%, but a modern nation has many more critical jobs that must be kept filled than a fantasy one does.

  • 1
    $\begingroup$ One hint: The research you point to duiscusses an army that returns before the begin of harvest, i.e. a campaign army, not a standing army. That means he discusses the maximum you can draft for a war. But you cannot keep an army this size indefinitely, they would starve everyone in no time. $\endgroup$
    – Burki
    Jan 22, 2020 at 8:10
  • $\begingroup$ @Burki: I acknowledge that in my 8th paragraph $\endgroup$
    – Kyyshak
    Jan 22, 2020 at 8:15
  • $\begingroup$ Yes you did, but i had the feeling that it would benefit from being made clearer, especially since the OP talks about a standing army (as far as it can be told from the question) $\endgroup$
    – Burki
    Jan 22, 2020 at 8:22

You don't need a modern military unless you're going to fight against one

Fighter and bomber jets are very expensive for a post-apocalyptic scenario when there's no real enemy that they can shoot at -- no other air forces or large-scale targets. It sounds like in your scenario the regime's enemies are "militia", meaning ordinary people and small groups with ordinary vehicles and small arms. While your government could target them with air strikes, it's not going to be worth the cost to fly a drone out, with a very real chance of it being shot down, and waste expensive missiles just to shoot one or two or three guys.

So, if your military's function is really just to crush the citizens and prevent them from revolting, what you need is lots of boots on the ground with small arms and just jeeps or trucks to get around. You're also probably doomed to failure in the long run; how long your tyranny can last kind of depends how hard you push people around, and whether you're doing anything to make it worth tolerating you (e.g. keeping away the zombies).

On the other hand if there are other major nations with navies and air forces, then the regime may try to maintain that kind of a military in order to fight against those countries. So what you might be talking about is essentially two separate militaries -- even if organizationally under the same "branch", they're carrying out totally different missions against two totally different kinds of enemies.


Build your 75,000 strong military. Then use it.

A whole bunch of hungry men sitting around waiting to fight is a drain on resources. Unless they fight. If you have the resources to feed and equip such a force, your army should be used for wars of conquest. You will build the United States back into the country it was bit by bit.

The Virginia Federation will probably see this coming if they are paying attention, and capitulate. If not, defeat them. Do not crush them utterly - they were your countrymen and you will want them on your side for the next campaign. Also they might burn their stuff if you are jerks and you need that stuff to feed your army.

You can sustain your army from the spoils of the places you conquer. And it should not be tough - people in the outlands were making the best of it but it has only been 10 years. They will probably be happy to be part of the United States again, especially when they see what your army is doing to their neighbors.


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