Just variegating this question for SEMI (NOT fully) automatic pistols like the M17 Modular Handgun System (variant of SIG Sauer P320) or Heckler & Koch P12. Pick whichever country and one of these pistols you want. Assume

  1. your country can manufacture it and bullets and suppressors, but subject to contemporaneous restrictions and resources. You can manufacture zero, or just 900 pistols to give to your general officers, politicians, and elite 1%. But you can't manufacturer too many, because pistols have limited effective range (50 m or 54.7 yrds) and you need produce other weapons.

  2. your citizens can carry both their contemporaneous primary weapon and this pistol.

  3. no other country has or can manufacture this pistol, but they can try to reverse engineer if they find or capture it like off your dead soldier. Assume other countries were as capable and knowledgeable as they were in real life.

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To what war do you need to send this pistol, before it can decisively impact the course of events? A decisive impact means anywhere from eliminating a major battle in the war to changing who wins the war. Killing one extra opposition soldier does not qualify, because it doesn't quite affect war outcome. For examples, SIG Sauer P320 won't affect

  • U.S. Revolution War because you can't outgun artillery, or cannon ball ships with P320. I know muskets were inaccurate, even if 100 m was their effective range.

  • US Civil War because you can't outgun rifles, sharpshooters or snipers with P320.

  • WW1 because you can't shoot down airplanes, tanks, or charge machine gun nests with P320.

  • WW2 because P320 won't protect you against U.S. atom bombs.

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    $\begingroup$ I think this question is does not have its scope sufficiently restricted. What's to prevent me from answering any war during Medieval times or earlier? $\endgroup$
    – DKNguyen
    Jul 29 '20 at 22:25
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    $\begingroup$ To clarify, who would be producing the guns and ammunition - historic country or modern? If historic, who is providing all the necessary machinery and expertise? $\endgroup$
    – Alexander
    Jul 29 '20 at 22:27
  • $\begingroup$ There have pretty much always been weapons that can out-range a P320. Are you saying a bow, crossbow, atlatl, or even a thrown javelin is superior to semi-automatic handguns? A semi-automatic handgun is valuable due to its size and range, but its fire rate is probably the best on the market until the mid-late 19th century, when machine guns started becoming feasible $\endgroup$ Jul 29 '20 at 22:29
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    $\begingroup$ I seriously question if anyone before, say, the Civil war could manage to build these handguns to the tolerances needed to make them effective. If, however, the designs were available in the civil war, I suspect they would adapt the loading mechanism to rifles rather than making pistols. Repeating arms existed in the civil war, but most governments weren't willing to shuck out the cash for really pricey guns. $\endgroup$
    – DWKraus
    Jul 29 '20 at 23:50
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    $\begingroup$ Classic "What if we introduce Weapon X?" question. The answer is always the enemy adapts. They capture some. They change tactics. They bribe. Or, most likely, they find clever ways to let the pistoleers waste their firepower on earthworks and fortifications and deceptions, and they will find clever ways to attack the pistoleer formations from outside their measly range. $\endgroup$
    – user535733
    Jul 30 '20 at 0:23

Actually I'd say anything before WWI. So here is an answer based on the little I know of strategy and warfare and also looking at the weapons themselves.

You said they won't impact the American civil war? Well. Let's examine that. Wikipedia says that the most widely used rifle was the Springfield Model 1861 that has this joke of a rate of fire Rate: User dependent; usually 2 to 4 rounds every 1 minute.

Now to range: Effective firing range 100 to 400 yd (91 to 366 m)
Maximum firing range 500 to 700 yd (460 to 640 m)

Now let's examine a pistol in the US military service, the Glock, just from Wikipedia to give us rough numbers.

Rate of fire for Glock 18: 1,100–1,200 RPM (rounds per minute)

Effective firing range 50 m (55 yd) (Glock 17, 17C, 18, 18C)

Now here is where it gets interesting I think. First the accuracy of those old rifles are a joke. There is a reason why massed infantry with rifles became obsolete. A modern rifle has terrifying accuracy and legality, so staying in the open means both armies achieve insane casualty rates.

Second the rates of fire are so absurd you might as well be using laser beams against cavemen. I know that all the bullets in the world won't help if any "snipes" you from double the range. But again those were not accurate, so trying to aim and kill a person with absolutely accurate and deadly pistols with absurdly higher rates of fire is much easier.

Also on the range. First is that even a 9mm round can kill you from a 100 meters or more. Those numbers are not reflective of how far will the bullet travel and kill. With simple iron sights and a short barrel you won't get far. But I'm certain that even at a 100 meters a 9mm round can still be effective if you train and properly use your army.

I have not tried any of that, can't even own a knife where I live, but videos on YouTube clearly shows ranges of a 100m is doable and even more are still believable.

Which leads me to the second point. You know how warfare is all about maximizing your advantages? Got cavalry? Get an open battlefield. Got phalanx? Protect them from skirmishers and the flanks...etc.

So the important point to a commander in command of such a weapon is to maneuver and deploy his troops where the range is not an issue. This is difficult, but most warfare is all about that honestly. So if the commander is at least decent, they will put their soldiers where 50-100 meters are enough, and their much deadlier rounds and insanely higher rates of fire can come into effect.

Perhaps such a commander can use the following.

Ranged cavalry. They were a thing right from the start. Bows, spears, darts, you name it. Even with gunpowder you had stuff like Dragoons and Cuirassier and many many other historical units utilized guns and special guns, usually shorter and hopefully faster, in their armaments. This makes it so that the cavalry can close the gap quickly, nullifying the range advantage, and produce a hail of fire that will annihilate any army.

Also "urban" combat will be completely dominated by the commander that posses semi-automatic pistols. In fact you can defend a city with much much smaller numbers because in an urban setting a modern semi-automatic will rule to points of broken video game levels of cheese. Also using cover and the fact that the older guns is not accurate only adds to the side with semi-automatic pistols coming out on top. And with no modern artillery, no tanks, no guides missiles, no drones...etc, flushing out defenders from a city is nearly impossible.

This can also lead to smaller more maneuverable units being more deadlier against the opposing army especially the flanks and the supply train. Again imagine armored cavalry with semi automatic pistols that uses hit and run tactics against a slower army.

That might also increase castle or forts or whatever. Purely military structures with reinforced walls that houses your little mounted devils.

So to answer your question, I'm positively certain that anything short of battle rifles, you know the historical ones from WWI and before, falls short of modern automatic pistols if used correctly.

You also need to understand that small inaccuracies, much like chess, can lead to bigger advantages in a war. The Roman army, just a famous example, utilized smaller supply trains and that alone changed history more than a mega super weapon. Same with strong English logbows or smaller mounted composite bows or fully plated knights...etc.

So to be clear I don't mean that an automatic pistol means: insta win. More like if used properly and in the hand of a decent general they will have a huge effect on the war.Sure if you drown your enemy in numbers in something like 10 to 1 battles you might count it. All is possible with enough resources. But that's a bit silly. But again most of the time even small differences can lead to big results on the battlefield. I mean Napoleon was not using plasma and Caesar was not leading demons...etc.

So yeah. Even against muskets semi-automatic pistols are amazing, and certainly every single war in history before that.

Edit: all that is you only counting the basic guns. Add longer barrels and better sight, or heck scopes, and they become way better than incarcerate old muskets with awful rates of fire and smelly powder that are long heavy and cumbersome.

Edit: as "Rhandal Allen" pointed out the Glock 18 is automatic. So here is what Wikipedia says:

"A semi-automatic firearm typically has an effective firing rate of 40 rounds per minute"

And looking for more answer it seems that 60–80 rounds is a good average rate of fire per minute for a semi-automatic pistol.

Obviously that's less than an automatic pistol but again that rate is absurd. And obviously there is a huge variety even within the semi-automatic world. Be it magazine or caliber...etc.

Lastly I wish to add that the "Heckler & Koch USP" has a Maximum firing range of 100 m (Wikipedia again) And that is actually pretty good for even modern combat. I mean sure a modern automatic rifle can effectively engage a target at 500 meters but without special equipment and good visibility your chances of hitting that target is pretty slim.

And according to this article the "Almost all interviewed stated all firefight engagements conducted with small arms (5.56mm guns) occurred in the twenty to thirty (20-30) meter range. Shots over 100m were rare"

Now I'm not sure about this because context is king here. If you are defending a perimeter then the distance might be higher and if you are engaged in urban combat you might be limited to lower ranges and so context dependent is the best answer.

Yet a number of 100-200 meters, I've actually looked up some google results for it, seems like a pretty good modern average.

So even the "range" issue is becoming less and less of an issue with actual statistics and actual combat examples.

So I stand with my answer. Also sorry for the mix up.

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    $\begingroup$ thanks. upvoted. but you used "Glock 18" that's FULLY automatic pistol. questions says SEMI automatic. :) $\endgroup$
    – user69651
    Jul 30 '20 at 2:55
  • $\begingroup$ @RhandalAllen, Thanks. I corrected the mistake and added an important point about ranges $\endgroup$
    – Seallussus
    Jul 30 '20 at 4:10
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    $\begingroup$ I should point out that modern rifles only have terrifying legality in the US and also you probably meant "lethality". $\endgroup$
    – Erik
    Jul 30 '20 at 7:04
  • $\begingroup$ Note that effective rate of fire is way less than 1100 rounds per minute -- there is no magazine available that can accommodate that (never mind the weight of such a magazine), and most likely the weapon would become prone to jamming if used in a sustained manner as a fully automatic weapon. A jammed pistol is no match for a bayonet on a musket. $\endgroup$
    – Randall
    Jul 30 '20 at 10:52
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    $\begingroup$ Note that more or less modern semi-automatic pistols are a bit older than WWI. The M1911, for example, is still a respectable sidearm today and the basic design is from 1911. $\endgroup$
    – Nolimon
    Jul 30 '20 at 17:00

If you can manufacture modern semiautomatic pistols, you can also manufacture semiautomatic rifles. Or automatic rifles. Or machine guns. You don't get the ability to make one without the other.

For that matter, there are conversion kits to add a stock to a pistol, adding a great deal of accuracy. Handguns are more limited by short sights and the inability of a human to hold them tight than by the ballistics of the bullet.

The manufacturing base would probaby be a good step towards making internal combustion engines, too. Working hard metal, tight tolerances, chemical industry to produce gun oil ...

A novel has been done where time travelers deliver AK-47s a bit over a century into the past. They opted for cheap Soviet assault rifles rather than Western models because they would get the job done.

In a way this question is similar to the one about warships two days ago. You should first think about an internally consistent way to deliver your disruptor into a historical setting, and then go with the logical implications of that.

  • Your premise could be a time traveler conveniently lost a 31st century nanotech suitcase factory that gobbles up raw materials and produces guns, magazines, bullets, etc. Only those are in the blueprint database. The finders can only fill the hopper and press one of the buttons.
  • Your premise could be a genius inventor came up with a modern semiautomatic pistol. And steel for the barrel. And the plastics which go into the grip. And the production line for the cartridge cases. And the chemical works for modern smokeless powder. But he steadfastly refuses to make anything but handguns. Sounds less plausible than the nanofactory, if you ask me. And then you have to explain why all the apprentices go along with that.
  • Your premise could be time travelers can go to the present-day US, sell gold/diamonds/whatever, and buy weapons. They are limited by the weight/size of what they can take home, and by civilian availability, which leaves pistols. Hand grenades would fit but they are not on sale, rifles are on sale but they do not fit. Pistols is it. But radios and night vision goggles are also on sale and smaller. Does the transit fry electronics?
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    $\begingroup$ Adding onto this answer, any semi-automatic pistol could be converted into a short-barreled rifle simply by adding a stock to it. $\endgroup$
    – nick012000
    Jul 30 '20 at 8:10
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    $\begingroup$ @nick012000, I wrote shaft rather than stock. Stock is clearer. $\endgroup$
    – o.m.
    Jul 30 '20 at 10:19
  • $\begingroup$ Actually handguns are pretty severely limited by the internal ballistics resulting from short barrels. A FN Five-seveN can theoretically hit a target at 1.5km with enough force to still be lethal to a human, but the short barrel means that even properly braced and used by a well trained individual it's not going to have useful accuracy beyond about 100m. This is part of the reason that it's not unusual to see race guns with extended barrels. $\endgroup$ Jul 30 '20 at 11:51
  • $\begingroup$ @AustinHemmelgarn, the same (short) barrel length gets a better performance in a longarm than a handgun, but an even longer barrel will of course help. $\endgroup$
    – o.m.
    Jul 30 '20 at 14:58
  • $\begingroup$ @o.m.: That creates other problems. Modern pistols use different (faster burning) powders than rifles. This is an example of what can happen with the wrong powder: bulletin.accurateshooter.com/2016/05/… $\endgroup$
    – jamesqf
    Jul 30 '20 at 17:31

Pistols generally have an effective range of ~50m against a single target. If your opponent is using shoulder-to-shoulder massed-infantry tactics like was seen in the late 1700s and early 1800s, then your likelihood that you will hit a useful target goes up dramatically at longer ranges.

A unit of men all carrying modern semi-autos are going to decimate a similarly-sized unit with single-shot muzzle-loading muskets. Even though the weapons are both effective to about the same range, the modern pistols have a vastly superior rate of fire.

By the mid-1800s, faster-firing rifles and repeating firearms start to become available, and the advantage drops quickly.

  • $\begingroup$ Thanks and upvote to you! "If your opponent is using shoulder-to-shoulder massed-infantry tactics like was seen in the late 1700s and early 1800s" But after getting obliterated by your semi-automatic pistols several times, won't your enemy change tactics? $\endgroup$
    – user69651
    Jul 30 '20 at 3:00
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    $\begingroup$ Back in college I did a paper for a US Military History class on the development of the machine gun and how it changed warfare. Reading quotes from British generals in WWI about how "the elan of the fighting man" with their rifle and bayonet will carry them to victory against modern weaponry was... heartbreaking. So, my answer to that is, "you'd like to think so, wouldn't you." $\endgroup$
    – Salda007
    Jul 30 '20 at 4:18
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    $\begingroup$ As far as "getting obliterated... several times", the US Revolutionary War (as one example) was fought over several years, but the total number of battles was fairly small, and a few of those were critical American victories. If Burgoyne hadn't surrendered at Saratoga or Washington had been defeated at Trenton, we'd probably still be singing "God Save the Queen" instead of "The Star-Spangled Banner". $\endgroup$
    – Salda007
    Jul 30 '20 at 5:14

"The musket is a good handle for the bayonet"

You have a lot of faith in the accuracy of Revolutionary War muskets. Here's a great article explaining why they were so inaccurate: https://allthingsliberty.com/2013/07/the-inaccuracy-of-muskets/ I would much rather have a reliable pistol with modern sights than a Revolution era musket. I think a Colonial army with SIGs would have turned the tide sooner.

There are a lot of important factors other than the effective range. Muskets didn't have interchangeable parts and there weren't many gunsmiths, so repairs were hard. And muskets were regularly damaged. Plus you're going to be firing at people clustered close together, which means you can hit somebody if you fire rounds beyond the usual effective range. The psychological effects of sending multiple rounds downrange while the British are reloading would be huge. You should also consider training. American militias were not especially well trained, so simplifying the operation of their weapons could have made a difference.

Those advantages apply in any war until after the Civil War. Improved reliability, easier repair, rate of fire, and reduced training needs are all force multipliers.

  • $\begingroup$ Note: a musket's rate of fire is something like 0.5 rounds per minute. A semiautomatic can probably crank out almost 50, and in both cases I'm talking about sustained rate. You can empty a clip at about twice that. Plus you can fire and reload while prone. One skilled soldier with a SAP could just about wipe out an entire regiment of musketeers. (The musketeers best hope is going to be to charge him and overwhelm him with numbers at melee range.) In comparable numbers, a unit with SAPs would be nigh undefeatable. $\endgroup$
    – Matthew
    Jul 30 '20 at 0:29
  • $\begingroup$ Trained soldiers firing smoothbore muskets could generally fire around 3-4 shots per minute, or maybe faster under ideal situations. Muzzle-loading rifles before the development of the Minié ball could only fire about one round per minute because the ball needed to be forced down the barrel in order to seat in the rifling properly. $\endgroup$
    – Salda007
    Jul 30 '20 at 1:27
  • $\begingroup$ Thanks and upvote to you! "You have a lot of faith in the accuracy of Revolutionary War muskets." I don't. I just forgot to mention their inaccuracy, but you're right. "I would much rather have a reliable pistol with modern sights than a Revolution era musket." $\endgroup$
    – user69651
    Jul 30 '20 at 3:02
  • $\begingroup$ Interesting trivia about muskets, there were other types of ammunition than the musketball. Flechettes had great aerodynamics and improved accuracy, but were expensive and difficult to manufacture in any quantity. Whereas shot-towers are fairly straightforward and repeatable. It wouldn't be incredibly difficult to modify a musket with a set of gunsights and provide ammunition with better aerodynamics and end up with something quite a lot more accurate $\endgroup$
    – Ruadhan
    Jul 30 '20 at 10:30

U.S. Revolution War because you can't outgun artillery, or cannon ball ships with P320. I know muskets were inaccurate, even if 100 m was their effective range.
US Civil War because you can't outgun rifles, sharpshooters or snipers with P320.

You don't outgun artillery. You make the artillery uselless. By not giving them a target. You don't give them a target by realising you don't stack your soldiers to have a better fire rate/hit ratio because you have pretty acurate fast shooting pistol.

Just imagine how Beretta 92F would prove itself in trenches compared to musket with bayonette.

Sharpshooters and snipers are rare they need easy target (like a tall, not ducking, hiding Sedgwick). With semi-auto pistol your whole tactics change. You can have small platoons with firepower equall to regiment. You don't have to wait for a battle. A 5 men cavarly unit that can just ride up and shot 400 bullets in less than minute. That would decimate any army.

  • $\begingroup$ "A 5 men cavarly unit that can just ride up and shot 400 bullets in less than minute. That would decimate any army." This was a tactic used in the US Civil War, except it'd be more like 50-100 men, and each one would have several pre-loaded revolvers instead of one semi-auto. It's certainly effective, but mainly as raiders against things like supply trains. Charging set infantry lines like that would've gotten them shot off their horses long before they could get within pistol range. $\endgroup$
    – Salda007
    Jul 30 '20 at 8:33
  • $\begingroup$ @Salda007 A 5 guys on horses are much more mobile, not against entrenched but moving army. 400 bullets is just those 5 riders having two guns and reloading each just once (and a half). you don't have to charge, you can choose any directions to attack as you're using weapon of short range, so naturally you want to close the distance to target faster than the target can shot you. Also it's harder to shot 5 very spread riders thatn for thsoe riders to ride along trench and just unload 15 bullet magazine. $\endgroup$ Jul 30 '20 at 9:12
  • $\begingroup$ Look into Mosby's and McNeill's Rangers from the US Civil War. They used basically the exact tactics you're describing, except with revolvers instead of semi-autos. They didn't "decimate armies", but they certainly sowed chaos and disrupted supply lines. ( en.wikipedia.org/wiki/43rd_Battalion,_Virginia_Cavalry & en.wikipedia.org/wiki/McNeill%27s_Rangers ) $\endgroup$
    – Salda007
    Jul 30 '20 at 18:08

Those pistols are still relevant in modern warfare.

In a very balanced modern conflict, having a good pistol as your secondary weapon can change the tide. Not with a decisive moment, but by the accumulation of small scale events where a reliable pistol can save the day.

In ancient time, you should not underestimate the power of modern handgun. The fire rate and accuracy of a modern pistol is similar to a gatling gun. A gatling gun you can put in your Pocket.

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    $\begingroup$ having a good pistol as your secondary weapon can change the tide. Please edit your answer to include an example of any battle where the presence of pistols made any difference at all. Pistols are for self-defense and are worthless for offense unless the opposing side only has pistols or less. $\endgroup$ Jul 31 '20 at 6:40

This site is filled with "if tech X is transported to time Y..." type questions. Most of it is insensible. So, as a frame challenge, I give you two answers that are both right.

Answer #1: They would affect every war past, present, and near future

If the people who possess them have access to a (practically) infinite supply of bullets & pistols, they would affect every war until the technology for all other weapons significantly outstrips the 2020-era pistols.

Answer #2: They wouldn't affect any war — past, present, or future

If there is a practical limitation of any kind (e.g., no combatant would have access to more than 10 mags of bullets in any battle), then there simply isn't enough firepower represented by a pistol to materially change the outcome of any war. Pistols can always be overcome by throwing enough people at them.

You could assume something between those two extremes such that there isn't enough of a limitation that there might be a line drawn sometime in the past before which the pistols would have a material effect but after which there isn't enough of a tech difference to make the pistols decisive... but then the question is story based because the line can be drawn anywhere by adjusting the amount and type of limitations.

Please remember, pistols might save the individual, but they won't save the battle or the war. If they were that useful, there would be no need to carry other weapons and the encumbrance of those other weapons would be put to better use.

And then there's the technology dichotomy. Your army/civilization has the ability to manufacture 2020-era pistols and ammunition... but not anything else? Don't you realize how much technology is involved in building such a weapon? It's frankly unbelievable that 2020-era weapons would exist in any but the smallest degree without the civilization being overwhelmingly overpowered in many ways. It's like asking if the Colt .45 had a difference against the North American Natives. There weren't just pistols and bullets — there were trains (transportation) and explosives (mining) and all the supporting tech (agriculture, cities, manufacturing/tech/education centers). The North American Natives didn't just lose because the cavalry had superior firepower. They lost because the civilizations they were competing with overwhelmed them in dozens if not hundreds of different ways.

Just one tech can't exist unless transported in highly limited amounts, which means the benefit they give is incredibly temporary.

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    $\begingroup$ cf "Guns, Germs & Steel", Jared Diamond. Most instructive, even if some (only) disagree violently with his premises. $\endgroup$ Jul 31 '20 at 6:54
  • $\begingroup$ @RussellMcMahon I've not read the book, but after reading a summary, it's basically correct. If one culture is technologically greater than another, the only hope the second has is in numbers (recalling the Iranian human wave attacks vs. Iraq's SCUD missles, etc.). The greater the divide, the less numbers matter. That's why my premise is basically, "throw enough pistols at the equation, and you can overcome any war. Limit the number of pistols, and you can choose which point in history you want to draw the line. A handful of pistols wouldn't affect anything." $\endgroup$ Jul 31 '20 at 7:00

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