# What's the most advanced weapon a time traveler from the 21st century could make with the technology of the Middle Ages?

Assume the time travel is a soldier who has a good idea of how to maintain and care for most guns and knows how all the parts fit together. They've brought with them a working assault rifle, a double-barreled shotgun, and a revolver, as well as a smart-phone with a solar-powered charger that contains a few encyclopedia's worth of modern knowledge.

I'm fairly certain that without industrialization, weapons that require precise machining will probably be out, as well as percussion caps and modern cartridges (even if you could teach the alchemists of the time how to make some of the stuff you'd need). Flintlock rifles and/or muskets would probably be possible I'm guessing, as well as some steam-powered weapons. But could you make a revolver or a shotgun work? It doesn't have to be as good as a revolver or a shotgun is today, so long as it is recognizably a revolver or a shotgun.

• "Middle Ages" when exactly? What was possible at the end of the 16th century was very likely not possible at the beginning of the 6th. And where exactly? In the 6th to say 12th centuries the (Eastern) Roman Empire had much better tech than Western Europe. Then Western Europe had better tech. – AlexP Mar 17 '17 at 17:00
• It's quite likely that both revolvers and shotguns could be made; I commend to your attention the Ring of Fire series which drops a West Virginia town from the year 2000 into the German region of Thuringia in the year 1631. The series explores the effect of the "up-timers'" knowledge and attitudes on the Europe of the Thirty Years' War, including technology that can be managed with an early-Renaissance industrial base. – Jeff Zeitlin Mar 17 '17 at 17:01
• Adding an "up-vote" for the Ring of Fire series. Especially the first, since that's where the majority of the "WHAT JUST HAPPENED?!" clashes between US and German folks happen. – CaM Mar 17 '17 at 17:13
• @AlexP End of 16th? The way I was taught, fall of Constantinople in 1453 was an arbitrary end of middle ages. Wiki quotes discovery of Americas (1492) and last year of 15th century (1500) as other possibilities, it also claims that Spaniards tend to extend it into first 2 decades of 16 century - some important Spanish royals died then. Either way it's end of 15 century, or at the very latest beginning of 16. – M i ech Mar 17 '17 at 17:18
• @AlexP 1648 is mid 17th century. I'm pretty sure you are confusing end of middle ages with end of renaissance. Also, it's hard to imagine how modern age could begin before late 18th century French revolution, as that was the first application of new ideas about citizenship, function of state, function of citizen etc. Everything before that, was some extension of Feudalism. – M i ech Mar 17 '17 at 23:26

(I feel bad about giving this answer, given how horrifying this weapon continues to be in the modern world, and how unconscionable it is to have it widespread any earlier in history, but...)

You are starting out with handheld weapons, but if it were me, looking to alter the course of warfare most simply and effectively in the middle ages, I would go with land mines.

Granted, this is a situational weapon, but all the materials you would need are widely available, and the weaknesses in medieval metallurgy aren't a problem.

The simplest version of a landmine is just a metal packet filled with gunpowder and a glass vial filled with acid. When a soldier or a horse steps on the vial, it cracks, and the acid drips into the gunpowder generating enough heat to set it off.

Your primary concern is going to be safety. No torches where you make your gunpowder. Do it outdoors, but keep it dry. Store it away from people. Combine the elements only when you are ready to use them. The vials of acid are relatively harmless, and the skills of creating them already exist. Don't put them in the mine until its already buried, though.

Your soldier should be aware of the tactics to best make use of these weapons, and the way medieval warfare was fought, the results would be devastating.

• Thinking about a land mind in middle ages combat is just... horrifying is an understatement. – Andon Mar 19 '17 at 4:51
• Another terror weapon -- Greek Fire, a version of napalm. This was credited to Kallinikos (Latinized Callinicus), an architect from Heliopolis in 672. Its use was very complex. When the Bulgarians took Mesembria and Debeltos in 814, they captured 36 siphōns and even quantities of the substance itself, but were unable to make any use of them. Besides the incendiary, the delivery mechanism involving pressurized nozzles was extremely important. A group of budding engineers with a good reference library could probably make great improvements in the middle ages state of the art. – HiTechHiTouch Mar 19 '17 at 10:50
• "Store it away from people" is certainly good advice. In 1769, a lightning strike on a church in Brescia in northern Italy resulted in a fire which ignited 90,000 kg (~200,000 lb) of gunpowder stored in the church, perhaps killing as many as 3,000 inhabitants of the city - see Brescia explosion. The Roman Catholic church withdrew its objection to lightning rods, which were viewed by some as attempts to thwart God's will, after the event. – moonpoint Mar 19 '17 at 15:35
• In regards to the Greek Fire comment, from Greek Fire, Poison Arrows, and Scorpion Bombs: Biological & Chemical Warfare in the Ancient World: Greek Fire was the ultimate weapon of its time....Partington, the historian of Greek Fire, compared the ancient reaction of horror to the modern dread of the atomic bomb. In 1139, the Second Lateran Council, following Western ideas of chivalry and honorable war, decreed that Greek Fire or similar weapons were "too muderous" to be used in Europe. – moonpoint Mar 19 '17 at 15:50
• It depends upon when in the middle ages this was. Reverse engineering gunpowder wouldn't be easy. At a certain point in the middle ages they would have black powder, but this isn't quite the same. They'd also have to recover one without setting it off, or they'd never know about the acid globes. Use them sparingly and mysticize it a bit. Stand on top of the tower with a pointy hat and a staff and point at the charging army just before the mine blows. It will look like magic. – IchabodE Mar 20 '17 at 3:35

Once you make nitroglycerin, you can stabilize it in the form of dynamite. Castle walls will just be decoration after that. Also, close formation fighting will be sitting ducks.

You can also make smokeless powder for bullets but the local steel may not be able to handle that.

If they have primitive firearms, you can introduce rifling. If they don't have firearms, you can introduce firearms.

You can refine oil into gasoline and have lots of fun with that.

If nothing else, you can use it to make potato guns to lob shrapnel wrapped dynamite into enemy formations.

If you need cash, figure out how they used coal tar to produce dyes and make a bundle.

• firing it out of a hand held cannon seems a very brave way to test homemade dynamite. – user25818 Mar 17 '17 at 22:57
• Heh. Just look for "sweat crystals" on the sticks. There are other ways to use it in combat. Heck, go all out. Invent gunpowder too and let the enemy see the rockets red glare. – ShadoCat Mar 17 '17 at 23:59
• Primitive firearms tend to fire shot or balls; rifling is only useful if you're firing bullets. And if I have to "go ahead and invent gunpowder", as you suggest in your comment, then presumably there aren't any guns around anyway. Where am I, in the middle ages, going to find crude oil and fractional distillation kit? Coal tar is an 19th century product: it was a by-product of municipal gas supplies being made by pyrolizing coal, and there was no such thing as a municipal gas supply in the Middle Ages. – David Richerby Mar 18 '17 at 11:21
• It is very easy to glibly say 'refine oil' or 'make nitrogylcerin'. Both of these things would be impossible or very dangerous with access only to middle ages chemistry and technology. – RoyC Mar 18 '17 at 11:55
• @RBarryYoung And that's why Alfred Nobel died penniless and wasn't able to set up any prizes named after himself. – David Richerby Mar 18 '17 at 17:47

## Biological Weapons

Armed with a modern high school level of education, you could wreak havoc. The Middle Age idea of hygiene was flawed at best and there were plenty of highly contagious deadly diseases floating around in large cities. Collect a sample, cultivate it and infect your target(s).

21st century disease prevention would also be pretty achievable in the Middle Ages. You can sterilize equipment with alcohol/fire, clean up with soap, protect yourself with gloves/face mask. Or depending on your moral compass, you could hire locals to handle the diseases for you.

• Protect myself with gloves made of what, exactly? There's no latex outside the tropics and no petrochemicals. So all we have is porous materials such as leather and cloth. – David Richerby Mar 18 '17 at 11:25
• @DavidRicherby I don't know that the gloves/face mask would be something you'd want to re-use. But it is better than nothing. You might be able to sterilize them between uses (with alcohol/boiling) but I would do experiments to see how this would degrade the leather. – NonlinearFruit Mar 18 '17 at 13:16
• They did do that. They catapulted plague victims over city walls, infecting everybody inside. contagions.wordpress.com/2012/06/28/… – Jim Pivarski Mar 18 '17 at 19:16
• @JimPivarski There was definitely cases of biological warfare in the Middle Ages. The time traveler would be able to evolve it from "this will kill bad guys" to "this will kill bad guys and not my friends". – NonlinearFruit Mar 18 '17 at 19:42
• Given the evolutionary arms race between various diseases and our immune systems, would you not already be a walking biological hazard if you turned up in the middle ages? Your minor sniffle could be something that would wipe out a country – LogicianWithAHat Mar 20 '17 at 11:54

With healthcare and agriculture. Nations would bow at your feet if you could feed them and keep them from dying quite so soon. The man who conquered the world with an open palm, not a clenched fist.

• Couple this with knowledge of economics. – HiTechHiTouch Mar 19 '17 at 10:52

The problems with modern weapons have been discussed several times, with all the problems of re-creating automatic firearms in a medieval setting. Basically, without industrialization everything must be hand-made, and even if they managed to make a modern firearm, with every single bullet carefully hand-made by master jewelers, it would cost so much it would not be worth it. Better equip 1000 men with slightly better than contemporary weapons than 1 man with a modern weapon.

Assuming they already have gunpowder, introducing standardized calibers, paper cartridges and the Minié ball would have a huge impact, without requiring any special technology or chemicals unknown to the era. The problem with chemicals would be, that even if you knew what it was, you could probably not locate it and start mining it, and even if you managed, you would need a large infrastructure to make use of it.

Assuming you could get into a position to explain your ideas to someone with enough power, you could make their guns much more effective with historical knowledge and very little to no new technology.

Standardizing calibers would make their guns much lighter, easier to load, and less prone to misfire, besides making logistics easier. They had rifled barrels in the early times, but they didn't use it much because it was a nightmare to load, prone to misfire, and you needed to clean your gun after almost every shot, or the residue caused the next bullet to be stuck in the barrel. With the ingenious idea of the Minié ball, you could make their gunners much more effective, by significantly increasing both their firing rate, range, and accuracy.

• Although it would be difficult to address the issues of precision and tolerance in the construction of rifled barrels to a specified caliber without machining, I believe that by using rifling mandrel's it would be just with the realm of possibility. – RBarryYoung Mar 18 '17 at 17:06
• @RBarryYoung : they had rifled barrels as early as in the 15th century, they were just very impractical and prone for the bullet getting stuck. The Minié ball would be very useful especially to compensate for the poor tolerances. That's the whole point of it: it can be smaller than the barrel but still make use of the rifling. – vsz Mar 19 '17 at 19:31
• And as per all the previous answers to this question, they also have to address the problem that high-quality iron and steel did not exist. So even if you can machine the metal accurately, the fact that they have no real control over impurity content and crystal formation means it's always going to be brittle as hell. Guns which explode and kill their users are not an asset. :) – Graham Mar 20 '17 at 10:56

Middle Ages is a bit vague, that's 1000 years of progress. What starts with men just armed in mail and shortbows end with crossbows, cannons and platemail. Now if he survives not being taken for a witch and killed I'm sure guns are possible.

Look up gun smithing in Japan. The Portugese sold them some arquebus they took apart. Fast forward two centuries(?) and they mastered the art and improved on them. Sure they were hand made and more expensive and European imports but they did it. With limited knowledge and access to outside materials.

Primitive break action shotgun seems totally possible. Late mediëval Europe had a great industry of artisans. Full body plate armor is quite the feat. Now if we're talking 600-700 things would be different.

• The full-plate armor you are probably thinking of is well into the renaissance - medieval armor never got quite that advanced (still mostly mail with some plate pieces). I will point out that the poor metallurgy of the time means iron still had a lot of inclusions in it - hand cannons were so cumbersome and excessively think because you could not rely upon the metal not having significant unexpected weak points in it. First you must teach them how to build at least 19th century smelters to make reliable steel... otherwise break-action is implausible. – pluckedkiwi Mar 17 '17 at 18:26
• i.imgur.com/elyIMg4.jpg 1450, still mediëval era plate armor. Looks like full plate to me. Hundred Year War, War of the Roses Both are still considered mediëval conflicts though yeah near the very end. And with his smartphone with encyclopedia I assume modern smelting is somewhat within reach. He didn't give us a timeframe so I assumed anything taht was possible in a few years was fair game. – Mormacil Mar 17 '17 at 18:31
• that does look a little more advanced than I tend to think of for medieval armor - I still think of harnesses with a breastplate but often neglecting back plates, and open cuisses and vambraces which only wrapped around about half the limb with the back/inner side just mail. For some reason I think of fully-enclosed plate wasn't until we started getting into the renaissance. I suppose when you generalize to such a broad period of time, you get quite the range. – pluckedkiwi Mar 17 '17 at 19:52
• Absolutely, hence I opened my answer that Middle Ages is a bit vague. So much happens between the fall of the Western Roman Empire and the start of the renaissance. Cuirasses with chest and back plating have been used with variable effect since the bronze age if we're pendantic :P – Mormacil Mar 17 '17 at 19:59

Kassam-type rockets (simplified version of Soviet Grad MLRS rocket) especially if you can also master real explosives for warhead (like dynamite). They already can be produced with access to very low-tech equipment and should be doable in middle age workshop. Would change warfare pretty quickly: no massive charge of cavalry, walls of no use, naval warfare would change fast, etc.

• You mean rockets similar to those used in Asia in the middle ages? – Mormacil Mar 18 '17 at 9:36
• Well, not exactly. Of course, every rocket, be it ancient Chinese one or Saturn V works on the same principle, but Kassam-type employs carefully constructed nozzles, rigid body, different type of propellant (based on common nitrogen fertilizer) and stabilizers, all together giving it much grater range and significantly improved accuracy, which technically makes it possible to use even in naval warfare. – user61244 Mar 19 '17 at 3:02

Money.

Someone armed with an encyclopedia and even a basic high-school education could make a lot of money with basic inventions. They could do that quite quickly.

Examples include steam engines (even rudimentary ones), metal refinement, agricultural devices, several people mentioned health and I'd emphasize clean water productions in that context.

Germ theory alone could be enough and basic antibiotics would be a great boon. An army armed with surgeons aware of how to clean water, sanitize instruments and surfaces, sutures and bandages would already be one people would be more willing to fight for because they'd be far more likely to survive injuries and less likely to die of infections (e.g. the major killer as late as the American Civil War !) and less likely to lose a limb.

Money, regardless of what period you're in, gets you power - that is, political power.

So I'd say your soldier needs to become a filthy capitalist. Using his military background and knowledge is one thing, but focusing on weapons production is not practical, as most modern weapons require the development of at least a basic chemical and engineering industry to be produced in effective numbers.

If, however, you insist on a weapon, then a rifled musket would be the natural choice for a soldier. But to be done on any practical scale that requires the development of these basic industries : power (steam), basic industrial chemistry, transport (again steam), precision engineering of toughened materials (mostly a combination of metal refinement and some engineering principles).

Money and political power will do more than a single weapon, IMO.

• Money requires everyone to believe that this piece of paper has value. The person who gives it value is usually a government or kingdom, but considering the constant wars at the time, governments change. – Muz Mar 20 '17 at 7:06
• Money need not be kept in the form of paper or currency. Governments change, currencies usually don't. It's usual that after the war/revolution/election the actual currency continues. Economic continuity is valued more than form of government. Paper contracts even tend to maintain their validity across change of governments. It's how financial dynasties are maintained. – StephenG Mar 20 '17 at 9:05

Weaponry has a broad definition, and most of the above comments give a great summary of the "killy-bits" you could create (gunpowder/rifling/etc). One thing I don't think was mentioned (and is pretty easy) is the screw-on bayonet. This would allow your newly-minted riflemen to protect themselves without the help of big formations of contemporary men-at-arms or pike-men.

Many of the major advantages you could create, however, often fall on the logistical side. A simple steam-engine is pretty straightforward, as are railway tracks. Both would be quite expensive to create given the tech of the time (the tracks in particular would be a bumpy ride, but if implemented it would give the owning country an immense strategic and economic advantage. Plus, your time traveler gets a ton of money charging people for it's use.

In fact, going with the steam thing, another very useful invention would be the steam-powered ironclad warship. This, combined with cannons, would have the power to sink any contemporary navy (as was shown during the Opium Wars, where the British first fielded the technology against the Chinese Navy).

Finally, modern financial systems like banking, joint stock companies, and paper money were almost unheard of outside of Italy. This may not seem like a weapon of war, but Great Britain's victory in the Napoleonic Wars was largely thanks to their economic and financial institutions giving them an almost unlimited amount of money to throw at the war.

• A bayonet isn't going to be as effective against cavalry as pikes. Also, "a ton of money" isn't going to be much use to you in the Middle Ages, since you wouldn't be able to keep it safe. Remember that, as you point out at the end of your answer, there was no banking system to look after it for you. – David Richerby Mar 18 '17 at 11:58
• @David Richerby you'd probably be ok actually, as the king would oftentimes let rich merchants use his vault to store their gold. More importantly, you'd do best to keep your money at work in hard assets rather than gold lying in a safe. Finally, you could just invent a bank. The first ones were just goldsmiths letting rich folks borrow their big vaults, so it isn't really "hard", once you have the idea. This wealth could then hire plenty of mercenaries, as the late middle ages were largely defined by those soldiers for hire. – Bert Haddad Mar 18 '17 at 17:24
• But that's basically my point. Having a ton of money in the Middle Ages obliges you to either trust it to the whim of somebody else who's capable of protecting it (i.e., to somebody who's capable of denying you access to it if they decide they don't like you any more) or to run your own private army (until the king decides that your private army is too much of a threat). That's very different to today's situation where you can just put it in the bank and rely on the police and the courts to keep it safe. – David Richerby Mar 18 '17 at 17:45
• @David Richerby Yeah, but usually the king would be trustworthy enough to hold it, and if he wasn't there were plenty of vaults to stash it. Money was basically just precious metals back then, and London's Goldsmiths had reliable vaults for their crafting materials, and eventually used them to store cash as well. Ultimately it's probably less of a problem than you're thinking, though it of course depends on the location/era you're visiting. – Bert Haddad Mar 18 '17 at 22:34

I would suggest reading "The Man Who came early" by Poul Anderson 1956, collected in Isaac Asimov's Great Science Fiction Stories 18, a fascinating description of how little could actually a modern man do "the modern man way" (weapon technology etc.) if teleported in the Middle Age.

https://en.wikipedia.org/wiki/The_Man_Who_Came_Early

Several VERY JANKY ballistic missiles, in addition to primitive firearms and rockets. You wouldn't have the tech to make an electronic guiding system, but once you calculate the arc of the rockets, you could take out towns from miles away. If you could gather a small army, you could easily take over most of Europe with your technology. Just don't try invading Russia.

If you have access to "a few encyclopedia's worth of modern knowledge" and a couple years time, I'd go with the combustion engine.

Let's see how well they do against a tank. I'd mount a flamethrower on top.

There's a big chance component, but: words/ideas.

If you use this multi-encyclopedic knowledge to successfully predict significant events and improve the commoner's life without getting executed for practicing dark arts, your growing status as a prophet or deity could make your words powerful enough to destroy nations, dynasties, and religions.

On the downside, you might have to martyr yourself to cement your legacy.

There are many military-related technologies that can be applied, although some of these are more like techniques/strategies/concepts that have military application

1. Gunpowder - primitive grenades, land mines, and breach-loading rifles would have a huge impact. If the metallurgy is too primitive to make rifles, then muskets could be fine - I imagine you could make some that were at least as fast to load as a crossbow and with more penetrating power.
2. Navigation - an accurate clock and knowledge of global trade winds would enable you to navigate in the open ocean on long voyages, granting your navy a HUGE advantage. Also, make sure to bring back some basic techniques for how to make ships more seaworthy in general. Reliable shipping and the ability to cross oceans would be quite valuable and would enable surprise strikes deep in enemy waters.
3. Food preservation and knowledge of basic nutrition/sanitation. Medieval armies were often forced to fight during a very limited campaign season. Knowing some of these basics would enable your army to campaign when your enemies cannot.
4. Nationalism. A time traveler would know some of what's required to inspire a population with nationalistic sentiment. This sentiment can be used simultaneously to improve army morale and decrease the power of the nobility, removing two major weaknesses of a Medieval kingdom (hard to campaign regularly if the people or nobility revolt)
5. Guerilla and commando tactics. With your advances in gunpowder and the loyalty inspired by nationalism, you can create elite commando units to operate deep in enemy lines, disrupting supply lines and destroying small, key outposts. Yes, that may have already existed, but you can take it to the next level.
6. Child care and sanitation. Guess what you need to fight a war? People. Guess what you get a lot of if you cut the infant mortality rate in half? People. Social norms change pretty slowly, so you should get a generation or two with WAAAAY more people than you really need. Welcome, recruits, to the glorious army of the empire!!!
7. The mentality of total war. A lot of medieval wars seem like children squabbling - people fight a whole year to snag a few miles of crapland and some ransoms. No, this time, we burn half their country to the ground and slay every male noble we can find. They try to invade? We scorch the earth, burn bridges, poison their supplies, booby trap the roads, and harass them from every side before annihilating their entire army. No ransoms, no survivors, no grudges to hold, since nobody is left to hold them.

I like this question a lot, always intrigued me. I am going to be a bit philosophical in my answer.

Having a revolver or AK-47 won't help much as they won't have the required technology and knowledge to recreate it, since its productions requires some sort of machinery.

Your character will effectively make the technological advancement that occurred historically take place much earlier and at a much faster rate. So I think it is best to see the single most important technology that will allow you to recreate our technologies in a more primitive way, the ICE - Internal Combustion Engine. This will allow you to create all sorts of machines and primitive mechanized weapons, and later could be utilized for electricity and quick logistic transportation, trains etc...

Think of a pike phalanx on top of an engine powered platform charging a line!

### The idea of the democracy.

Ha-ha-ha, I only joked. Normally, I don't post popular bullshits with the intention to collect many upvotes, but it was so obvious that I couldn't miss it.

The democracy was well-known already since the ancient greeks, any educated people in the medieval age knew that it existed, and that it would be possible also in their era, and they rejected it. If a strange alien - arrived probably from far, far away, from a terra incognita (this is what they would think from a time traveler) would propagate democracy for them, they had laughed on him. They would say around so: "look these primitive peasants, they can't even read, they can count only until 10, except whose fingers were already cut! And you want them to select our King? Look, what Socrates wrote from their "democracy", it was actually the rule of the idiots!" So, the idea of the democracy would be totally ineffective, it is nearly sure.

### So, don't have illusions, a weapon means a weapon and not an idea.

It should be a primitive weapon. You can't get even an AK-47 (alias Kalashnikov) with you, because they don't have the required metallurgic industry to reproduce and service it.

Here comes the next problem: any machine - also the weapons are machines - were produced by other machines. With your pure hands, you can't produce anything. Maybe with a lot of weaponsmithy work, you can produce a steel tube (what will be the barrel of the AK-47), but it won't be enough precise. The bullet won't be able to leave it.

On the end of the chain on machines produced by other machines, there are always human hands. Human hands, shoveling coal into the steel forge, controlling the machines casting the iron, and so on.

What they didn't know:

1. They didn't know the exact chain, how to produce finally AK-47 from the people having no machines only hands.
2. They didn't knew the explosives.

But they had a lot of smart people. Consider Newton, Galilei - millions and millions people had existed with their mental skills also in their era, but they never became well known. Most of them died as a peasant, and they were known only in their village, because they were the other (after their priest) who could read.

So, take a lot of good books with you, with university text books about metallurgy, chemistry.

Take some explosives, too, and an AK-47.

You will be a chief scientific advisor of a local power, maybe even a king. In some decades, you will be able to produce an AK-47.

It is very important to get enough supply to show a local potentat, that you can produce unimaginable weapons. There is no such stupid power in the era who couldn't realize its importance. It is the result of a selection mechanism: anybody decision maker underestimating the worth of the weapons, had been long conquered by others who hadn't.

• This reads like a rambling rant. It's not really clear what relationship, if any, democracy has to weapons. I think I understand what you're driving at, but I have to leap a lot of gaps in your writing to make my guess. – Wildcard Mar 18 '17 at 2:25
• @Wildcard It was only a joke. :-) I estimated there will be other answers saying some revolutionary idea, particularly this. The essential part of the answer is that he has to pack 1) weapons for demonstration purpuse 2) metallurgy and chemical knowledge, in books. 3) with the demonstration, he could get the attention of a local power, and 4) with the (human and material) resources provided by him, he could build a heavy industry in some decades. – Gray Sheep Mar 18 '17 at 2:30
• I disagree; I think almost any modern technology would serve as an attention-getter. Or even just the modern knowledge itself could be sufficient, if it allows you to plumb hidden secrets of the local technology. The subject of the question is actually a very common theme in fiction; Deathworld 2 by Harry Harrison comes to mind (sometimes published as "The Ethical Engineer"). – Wildcard Mar 18 '17 at 2:47
• @Wildcard I think it is right. The traveler has to find an enough strong potentat for its defense. But: if you can't show weapons, you can't convince the local powers with anything to get their support. From that point, you have to break through the walls before their culture, it is chanceless. If you show weapons for them, yes it is an attention-getter. But if you don't get their support, you can't make anything, to build even a simple steel factory is impossible for a single person. Furthermore, even these factories is such a big skill which require a lifelong learning of – Gray Sheep Mar 18 '17 at 2:53
• @Wildcard of professional engineers. The schematic diagram of a Kalashnikov is simple, but to produce a factory where all of its parts can be produced with 0.01mm precision, it requires the cooperation with hundreds of people, the traveler alone surely won't be enough. – Gray Sheep Mar 18 '17 at 2:54

How about a railgun? You could probably manage wire, electricity for big electromagnets and some kind of timing mechanism. The mechanism itself wouldn't have to be that well crafted. It would probably be pretty heavy to be lethal.

• I was wondering what the "timing mechanism" is for. I guess you mean a multistage coilgun. – ChrisW Mar 18 '17 at 2:16
• I don't think mediëval manifacturing could come close to the power requirements needed to power a railgun. – Mormacil Mar 18 '17 at 9:35

You very well could make a fully functional gun, such as the AK-47 or revolver, with enough time. Since you already have one, you could simply disassemble the one you have and use it's parts as a blueprint for blacksmiths of the time to create them.

They had the technology to create keys and locks, so issues of creating small pieces of shaped metal are negligible, or at least, functional enough to be usable in the crafting of a gun.

The only part I'd consider a bit more complex would be the creation of gunpowder. The creation dates back to the early 1100's at least, so the idea of it may well be propagated, as it was used in grenade-style weaponry at the time (mostly in Asia). If it's stable enough, it should be able to be used as-is, though I'm no gunnery expert and I'll leave that for the gun-nuts to speak on.

As for the machining, it's 100% possible.

• Two things, the OP implies with the Encyclopedia the formula for Gunpowder can be know. Any Alloy's and techniques/technology can be known. Actualy pretty much leaving just the workmanship. There I would disagree with the OP. Industrial Machining may be more applicable for mass production but I do not see it as defining a skilled/quality set of appropriate craftsmen could not crank out equivalent or better weapons and ammunition. The other thing I see the OP doing is thinking that because they didn't means they can not. Instead, Seeing is believing ... they were not stupid. – Enigma Maitreya Mar 17 '17 at 23:13
• You seem to assume that the only reason that Ivan the Terrible didn't have AK-47s is that he didn't know the design. That just isn't the case. There is a huge difference between making primitive locks and machining parts for a modern firearm. You need tight tolerances and that's only possible with mass production. You need modern materials. You need a way of mass-producing bullets and transporting them to the battle. You need a propellant that's better than gunpowder because gunpowder residues aren't compatible with the tight tolerances you need between barrel and bullet. – David Richerby Mar 18 '17 at 11:44
• Quite simply, you cannot make an AK-47 out of wrought iron using a hammer and an anvil. – David Richerby Mar 18 '17 at 11:44
• @Psychrom Twaddle. Modern firearms like an AK47 totally do not use gunpowder. If they did they'd jam after about two shots. – BlokeDownThePub Mar 18 '17 at 21:03

I know that I come too late to the party, but I'd say the most useful weapon would be a flamethrower. Petroleum was considered useless or a poison in the middle ages, but it wasn't unknown, and the rest of chemical ingredients for napalm were already known by alchemists.

A small barrel with a hand pump and a single heavy armored dismounted knight could destroy the tight formations of soldiers which have been the norm until the invention of the machine-gun.

Last I looked, there are 8 decades yet to go till the end of the 21st Century. Most advanced weapon is yet to be thought of yet, probably.

Towards the end of the last millennium, economics considered labor, capital, time, and information to be the four resources used in economical production. I'd add land to that.

You mention a single soldier and a couple of pretty useless weapons brought with him/her. (They're nearly useless unless there is some stockpile of ammo and spare parts for them). So, this soldier is going to magically become an influential member of some aristocracy? ..OK.. And s/he will magically have wealth to spend (capital)? ...OK... As well as the labor (workers)? ? So, given all that, which doesn't sound very plausible to me, then what could he build? In a month? or in 20 years? Makes a big difference.

I'd probably go with mortars. That's assuming we want to limit it to small arms and not things like weaponized anthrax or bubonic plague, and that dirigibles and propaganda don't qualify as weapons in this scenario. The most "advanced weapon" I can think of would be a radio. It could broadcast "messages from God" for the faithful to pick up arms and join my Crusade.

I find your question too vague. What would the goal be of the soldier? What are the limitations in his resources? What society would he be in?

In reality, anyone from the present era finding themselves in the year 1600 would probably have a very very short life expectancy. They'd be robbed quickly and since they couldn't speak the language, would have virtually zero power.

BTW, you're not going to be able to build a forge and make steel from the information available on wikipedia or Encyclopedia Britannica. You need more specific information than the superficial stuff you find on-line.

• Hello and welcome to WorldBuilding! Your text would be far easier to read if you broke it into multiple paragraphs. Furthermore some of those sentences sound a bit negative towards the OP, like the ones ending in "..OK..". Moreover: if you want clarification from the OP it is better to write a comment and ask for the clarification. Otherwise the OP could provide that information and thereby invalidate your answer which is something we don't like around here. You can comment once you get 50 reputation. – Secespitus Mar 17 '17 at 19:06