How could a time traveller change medieval history using only modern knowledge? [duplicate]

Question

How could a time traveller from our era change the outcome of a medieval battle using only knowledge of history, geography and modern science?

Lets suppose our time traveller is a learned person with a good grasp of at least high school science and history.

He / she has the ear of the king and has prep time of up to six months to a year before a decisive battle is to be fought against a foe with superior numbers, whom history decrees will win the battle

Chemistry: Gunpowder was my first thought, but getting access to base ingredients would be difficult.

Physics: Better siege weapons, perhaps more effective trebuchets, but these won't help with a confrontation between two armies on the field

How does our traveller make a difference?

Answer 1

Trying to implement modern tehnology in a short time is a non-starter. Don't go that way. Use the local tehnology and military knowledge augmented with the unique intelligence opportunity brought by the special advisor.

They are a time traveller, right? So they know (1) how large is the opposing force and its composition, (2) when it will be assembled and where, (3) what route they will take and (4) where the battle is to be fought. Using this knowledge they can instruct the king to:

• Assemble a larger force. Medieval armies were tiny. Any half decent kingdom could easily assemble a larger force than what the enemy thought was enough -- in medieval times the real problem was the abysmal logistics, so, if the king knows precisely when and were to assemble to host it should be easily feasible to achieve superior numbers.

• Counteract the composition of the opposing force. The enemy comes with heavy cavalry? Prepare the field with caltrops, masked ditches, and other anti-cavalry surprises. If they have a little time they could introduce effective anti-cavalry tactics, such as pike formations. The enemy relies on Genoese mercenaries armed with cross-bows? Fight behind field fortifications. Surely the generals will know what to do if you tell them in advance what the enemy will bring.

• Choose a better battlefield. The time traveller knows the route and the schedule of the opposing force: the generals of the king can exploit this knowledge to choose a battlefield which favors them.

• By knowing the size, composition, route and schedule of the opposing force your side can easily achieve strategic surprise; if they can't they amply deserve to lose. Launch a pre-emptive attack. Attach the opposing force en route. Defeat the opponents in detail before they can concentrate their forces.

Answer 2

The first and most important thing to teach, and one that also can be applied in the available time, is hygiene, as mentioned by others. I remember reading that in medieval times soldiers often weren't allowed to remove their uniform at any time. Dump that stupid rule and make them wash. Also, make them wash their uniforms. Aside from other things it will also mightily impress the opposing army.
Once you got them started on hygiene, make sure they understand that latrines are to be built away from water sources.

Next, teach them about logistics: Make sure your own troops are well provisioned. And focus your military attention on disrupting the enemies supply chain, whenever possible by taking their food for yourself.
And teach them that pillaging your own farms is really a stupid idea.

Then, discuss tactics. Training infantry was not horribly difficult, but it's still a good idea to make sure that you have as many battleworthy troops after a battle as possible: There's likely to be a next battle, and once the enemy notices that your army is nearly as strong as before, it will diminish their morale. And their troops... And after the war there are fields to tend to, which is also easier when you haven't killed all your labour force.
So, teach them not to brute-force battles, but to employ hit-and-run-tactics. Teach them that killing the enemy commanders is much more efficient than facing an entire army up front.

In short: Avoid battle where possible, and never let the enemy dictate the playground, or the rules, and most of all, never both.

And after the battle, wash. Use soap. pillage the battlefield and burn the dead. And wash again.

Answer 3

Communications. Semaphores.

In ancient times it could take weeks to get a message from one side of the country to the other. The semaphore first appeared in Europe in the 1790s, and suddenly commanders could send and receive data within minutes. This gave them a huge advantage.

It's easy to build one with low tech, with flags and levers on a hilltop, or to do it manually (I learned to do this in the Brownies). The hardest part would be disseminating the code. You would need your own code to stop competitors reading it.

edit: add to that, send messages at night using blink code and a covered lantern. You don't need a lot of text to send standard military messages, you just need a code worked out beforehand, and change it regularly. The covered lantern has the advantage of being directional, instead of the semaphore on a hilltop which can be seen by everyone.

Answer 4

Some ideas:

Steam machines: Are not that difficult to build for an experienced blacksmith. You may get ironclads and other steam machines.

Distiled Alcohol: It's highly flammable a not so difficult to get from wine or other alcoholic beverages. You can create plenty of machines being fueled by alcohol.

Optics: Not that difficult if you have people who know how to make glass works. You can get binoculars and lenses.

Hot Air Balloons: Not difficult to make. They would give archers some advantage and would frighten your enemies.

Compressed Air Cannons and Catapults: Once you know how to build valves and gears is not that difficult.

Methane: You can get this powerful gas from animal faeces and decomposition.

Answer 5

This is kind of broad, but anybody with sufficient modern scientific knowledge and modern combat tactics can potentially determine the outcome of any battle in the medieval times.

While the possibilities are almost endless, here are some which I thought would be the easiest and the most effective.

1- Use historical knowledge and battle specifics

Someone from our times would know the details about the particular battle and how the armies were arranged, which weapons were used and what were the strengths and weaknesses of each side. With this hindsight knowledge, you can easily overcome your party's weaknesses and focus on the weaknesses of your foe. Knowledge is power, and future knowledge is like nuclear power!

2- Utilize biochemical weapons to decimate and demoralize the enemy

You have lots and lots and lots of options here. Coat your arrows and spears with venom collected from snakes, scorpions, spiders, poison dart frogs (central and South America only) and hornets. For mineral toxins to coat your blades, use corrosive sublimate (HgCl$_2$), phosphorous salts and sulfide salts. In plant poisons, you can use oleander, calotropis, digitalis, bushman's poison, strychnos, datura, rosary pea, wolfsbane, hemlock ... (and a couple dozen others. I think the point has been made)

3- Utilize wind!

Before the battle, when the armies are camped in front of each other, if the wind is blowing from your side to them, burn noxious chemicals so that the fumes are blown toward your enemy, causing damage and panic. Large torches, coated with a mixture of crude oil, sulfur and powdered oleander will do the job nicely. The fumes will be acidic and toxic, not only inducing cough and teary eyes, but also causing panic and decrease the morale of the enemy.

4- Use blinding beam to disorient your enemy

You would need many mirrors of 1 square foot size. Install the army of these mirror holders (about 300 of these will do) at some out-of-reach location (e.g. at the top of a very steep hill). They will focus the reflected sunlight beam at the enemy's soldiers (specifically targetting archers and cavalry). While they will not be able to set anyone on fire or inflict severe burns, they will be able to blind them and create panic and disorientation, helping your side.

5- Implant poison coated punji sticks in the way of your enemy

I mean these.

Considering that you (the time traveller) in hindsight, knows which path the enemy will take to the battlefield, you can easily deploy tens of thousands of these pointed sticks with poisoned tips, in his way. You can plant them in the jungles and woods in his path and you can lay punji traps for him, by digging up pits, planting punji sticks in them and then covering up the top with a thin layer of grass and sticks. Given a couple weeks, the upper layer would completely naturalize with the earth, making it impossible to see the trap.

The results would be simply disastrous for the enemy.

6- Use caltrops to disable cavalry

These are caltrops.

Prepare lots of these and give at least a couple dozen to each foot soldier and cavalryman in your army. Utilize them to disable fast cavalry attacks during the battle. Simply throw the caltrops in the way of the invading cavalry and many of them will never reach you at all. It will also slow down the approach of the remainders, as they will have to watch out for these deadly spikes.

Final Word

There are many, many more methods you can deploy, but I thought these would be the easiest and most potent ones. The medic improvement and steam powered catapults (which I don't think can be built during a 6 months time) have already been mentioned by other users, so I do not need to reiterate any of those.

Answer 6

Pasteurization

Medieval logistics were a mess. If you introduce foods that can be mass-produced and stored for weeks or even months then your logistics would be simplified a lot, which makes your armies A LOT more effective.

Just make sure people are aware of scurvy and eat their sauerkraut diligently.

Also, screw famines.

Better looms

Introduce flying shuttle and mechanise your textile production. You can rake GDP-level lots of money this way if you can scale your production.

If you leverage those, you'd have both military and economic advantage.

Answer 7

Modern medicine will help a lot, reducing the number of people dying from wounds. I am talking about knowing germs exists and being able to cultivate penicillin, with that you could reduce the number of deaths greatly. Hygiene will keep your soldiers free of illnesses while knowing the importance of vitamins (found around renaissance era) will keep them strong.

Steam power will also help to power catapults and similar siege weaponry. Increasing their power and reducing the number of people manning them.

Answer 8

Politics.

If you came up of a really good invention - you will still have to build it using the medieval materials, and then produce it in big numbers, and then train soldiers to use it.
If you only have a year, you probably don't have the time for that.

But you got the ear of the king (umm, I hope not literally), so you can at least win more time, or maybe even avoid the var.
You probably know the situation in the opposing kingdom. Maybe you'll be able to find a common enemy, or to spark a rebellion there, or to provoke it to attack some other country first. Maybe try to appear more threatening (showing off steam engines?), or more useful as an ally (penicillin trade pact?).

But in the meantime, yes, keep improving mining, medicine and hygiene. You probably will be attacked by someone else, anyway.

Answer 9

So, there are a few major "any modern person would know about these" things that your time traveler could convey. They wouldn't necessarily win the battle, but they would improve the overall conditions of your army and thereby increase your odds:

• Basic hygiene: Wash your hands and faces, and ideally the rest of yourself, and use soap! Don't eat rotten/old food! Diseases are spread by germs, which can be spread by body fluids or contact (though different diseases use different methods), so cover your mouth when you sneeze or cough!
• Medical hygiene: use distilled alcohol to clean wounds before binding them to prevent sepsis! Clean tools and surfaces with distilled alcohol or dilute bleach before using them!
• Lead & Mercury, dangers thereof: That stuff's poisonous! Don't make cups and plates out of it or use it for plumbing! And stop trying to use Mercury as a medicine for anything!

You specified that your time traveler knows high-school chemistry. If they remember the medieval names of various chemicals, then they can advance chemistry by a few hundred years by teaching the kingdom's alchemists all sorts of interesting combinations. The ones pertaining to warfare mostly involv aqua fortis (aka nitric acid) and vitriol (aka sulfuric acid).

One low-hanging combination is aqua fortis + cotton (+ vitriol optionally) = guncotton. It's like gunpowder, but more powerful! Keep it dampened with dilute alcohol, though; it's very sensitive. Use it to fill artillery shells or grenade-type bombs for increased explosive power. With a some (rather explosive) trial-and-error, they might also be able to use it to make smokeless powders for their firearms. This does depend a lot on the strengths of the acids used, though, so it may still be beyond the resources you have available.

As @nzaman mentioned in their comment, gunpowder was already well-known to the medieval world. However, early firearms were finicky and unreliable; it wasn't really until the development of the flintlock musket in the mid-1600s that they really came into their own. So if your time traveler is familiar with how flintlocks work, then they've got a head-start there, too. But there's a simpler firearm-related invention that can give your side a distinct advantage ahead of its time: the Minié ball.

Rifles were known as early as the late 1400s, but early rifles were unreliable and slow to load, since the lead ball had to be hammered into the barrel to engage with the rifling of the barrel, and the gunpowder quickly fouled the rifling. The Minié ball revolutionized gunpowder warfare by letting the bullet expand to grip the rifling when fired, making it as quick to load as a smoothbore musket. Also, the conical shape and better seal against the barrel gave a higher velocity, and thus better penetrating power. Medieval armor was frequently "proofed" against bullets, but only the low-powered, short-range weapons available at the time, not modern rifle bullets. If your traveler still has problems, they could experiment with adding a hardened steel core to the bullet as a penetrator, but that's probably overkill.

So now your force has accurate, high-velocity rifle fire from significantly longer ranges than the enemy is expecting. The same methods scale up for cannons, improving their range and accuracy as well.

Also, the time traveler should also pre-invent the bayonet, so that their army doesn't need dedicated pikemen to protect against melee attacks or cavalry charges.

Now they are effectively bringing a mid-1800s army to a medieval fight. Have fun!

Answer 10

Depending on how technically savvy this person is, the time traveler would actually be able to create a stream engine and kick start the industrial revolution by simply introducing the people to this technology. He could also introduce electricity and make generators driven by the previously introduced steam engine. With enhanced industry the production of armor and weapons can increase granted they manage to set up production soon enough.

With the introduction of the steam engine new ways to conduct agriculture also emerge. With this new technology they can easily establish a way more efficient resource production and likely higher quality armor and weapons, thus overwhelming the opponent.

On an even longer time, with the technological kickstart the kingdom received it will soon surpass technology and wealth of every bordering kingdom.

Answer 11

Let's assume our TT have no knowledge of this battle so he can't prepare and predicts for particular moves.
So chemistry - gunpowder is safe and easy choice, there is such things as "difficult ingredients", it's just coal, sulphur and potassium nitrate that had to be imported from India anyway. Then comes to mind hydrochloric acid or sulphur acid. You don't need much to have a great psychological impact on the enemy. Second one is mustard gas (because if you have hydrochloric acid you can make mustard gas).
But that's just dirty tricks. If you want to play clean then:

• better mining equipment for trenches and pits
• entanglements
• artillery (balistas made with modern physics and more efficient ammo)
• Smaller army means better equipment for fewer people is needed, better armour with more movability, better training and more diverse use of cavalry.

Answer 12

Well in my opinion, I do not think big inventions are needed to win battles of the middle ages, rather knowledge and strategy.

In the first place the armies of that time, were usually disorganized and formed in its majority by units of cavalry (usually heavy cavalry), light infatneria and archers.

Having full knowledge of the strategies used in antiquity, it is not difficult to organize an army difficult to defeat. Based on knowledge of minum complexity:

• Better use of pikes:

Units such as the Landsknecht, the Swiss Pikemen or the Spanish Third developed very advanced and effective tactics in combat with the correct use of the pikes, was such the effectiveness of these units that came to be used in the conquest of America.

The tactics of these units were very effective against the heavy cavalry, main force and power of the armies during the age.

• Use of repetitive crossbows:

These crossbows already existed at this time, but were not widely used due to various design problems, which with a couple of current improvements (simple improvements) could turn into terrible weapons on the battlefields.

• Use the cavalry, but do not depend on it.

Cavalry was a very expensive unit during the middle ages, especially heavy cavalry. So losing these units meant a higher cost than other units, so you could use a smaller amount.

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Having made the choice of the previous army, I developed the strategy to follow.

The combination is as follows, compact groups of pikemen with large pikes with at least two rows of pikes, on the third row crossbowmen and groups of heavy and light cavalry on the flanks.

Using the tactic developed by Alexander the Greater, "the hammer and the anvil", but now we will have a better cavalry to attack the flanks and much better lines of infantry protected by crossbowmen in case of attempts of attacks of the rival cavalry.

In addition most of the armies of the middle age that depended on the cavalry to win the battles, could not do it since to throw the cavalry against our lines of piqueros would be a suicide

Answer 13

Generate electricity using waterfalls and so on just to make some electric fence. You don't need a precise, steady voltage/amperage, you just need to electrify some wires/gates as specific points and that will stop many troops. Great for defence.