How would armour (and combat) change if the fighter didn't need to actually wear it?

Through an arcane ritual, a warlock-knight forms a bond with their squire: thereafter, the squire wears the armour, and the warlock gets the benefit of it. So any force (be that hand, weapon or environment) incident on the space above the warlock's skin where the armour would be, is magically transferred to the armour (in the same place and at the same angle of incidence relative to the armour) as worn by the squire. The warlock doesn't need to suffer the weight or awkwardness of the armour themselves.

The warlock and squire don't need to synchronise their movements or orientation, or even be on the battlefield together, although the only way the squire would be able to anticipate impacts would be by watching the warlock. Any blows which penetrate or bypass the armour injure the warlock, not the squire (it's as though the warlock is wearing an invisible, weightless set of (I presume) full plate), but the squire is affected by forces transferred through the armour.

What armour and combat techniques would these fighters develop to maximise their advantage from this ability? How much of an advantage would it give them over ordinary combatants?

If the squire dies, the bond is broken and the warlock is left in the middle of the battlefield with no armour at all, which is obviously a Bad Idea. So while the squires are considered subservient and ultimately disposable by the warlocks, they have to give at least some consideration to their welfare.

Setting is medieval fantasy, good metalworking skills but no gunpowder. Warlocks would have the financial resources to equip themselves and their squires with the best weapons and armour available.

Update some great (and hilarious!) answers here. To adjudicate on a few questions:

• Armour needs to be 'quite close' to the skin to transfer via the ritual, so no tanks or shields. But I can't see why spiky protrusions shouldn't function as weapons.
• The invisible armour wouldn't block light or heat flow to the warlock, but I can see the argument for it blocking airflow to the same extent as the real armour.
• How to deal with the conservation of momentum and energy is currently why the pile of used scrap paper in the corner is growing so rapidly :p The invisible armour retains the same absolute position relative to the warlock's limbs as the real armour is relative to the squire's limbs, so if you hit hard enough with a hammer that the armour gets pushed into the skin, then the hammer will be in contact with the warlock and is bound to transfer some energy/momentum. But for proper application of the Rule of Cool I think it should be possible for a warlock to stop a mace dead with a bare arm, even if that means a squire going flying behind the scenes :)
• If the armor have some protrusions (large Pauldrons, spikes or blades) - will they function the same way as the armor? If "yes", this magic ritual can provide the warlock with weapons too, not just armor. If "no" - where do you draw the line between heavy armor (compatible to the ritual magic) and offensive equipment (incompatible with the magic)? – G0BLiN Aug 14 at 15:22
• How the blunt force & momentum is shared between warlock and squire? For example, the warlock is struck with a mace - a blow that does not penetrate armor, but knocks someone off his feet. Who would be knocked off - warlock or squire? If warlock, would the squire feel anything at all? – Alexander Aug 14 at 17:08
• also is there a limit size or gap/space against the armor to the wearer ? is it need to be tight to touch the wearer (squire) skin or body or can the armor have some loose gap/space in it ? and can the magic turn on and off as the warlock like or a permanent thing until the squire die? – Li Jun Aug 14 at 17:58
• Most importantly if impact/pressure force goes to the squire, the warlock cannot be moved (eg. on a cart), because any pushing pushes the quire instead. – Tomáš Zato - Reinstate Monica Aug 15 at 8:16
• @Chronocidal I think the goddess Handwavia declared that the last person who tried that amputated their arm by flexing their elbow to the point where the invisible armour was intersecting their upper arm, then trying to straighten it again, and since then warlocks have restricted themselves to more orthodox armour configurations ;-) – Stephen Aug 15 at 12:27

You've removed the weight/protection tradeoff, so your lucky squire is going to be moved around on a cart because they're wearing so much armour. You've also removed the sensory/protection tradeoff, so your squire will be effectively blind and deaf for the duration of the battle. Why would they need eyeholes, after all?

You can have huge armour spurs sticking up from the chest and back and shoulders to protect the neck. The head and chest can be armoured to the point that they may as well be indestructible. Limbs can be slightly better protected, but the need to keep them flexible limits quite how crazily you can beef them up. Big forearm and shin guards will work nicely, and as you don't have to worry about getting tangles up in big spurs you can have sticky-out bits to help protect the knees and elbows, too.

Also, why bother with metal for everything? Its a useful thing for wearable, portable armour, but now weight and to a certain extent portability isn't such an issue, so you can have big chunks of stone or wood.

Super thick arming jackets that would cook an energetic combatant to death are fine, even in the depths of summer, because your squire can be left in the shade with someone sloshing water on them from time to time whilst the warlock runs around wearing whatever the hell they like.

To dampen impact forces, you can string the squire up like pinata. That way, heavy blows will swing them around, but won't cause crushing damage. Do make sure that if they puke, there's a way for it to run out of their excessive head armour without drowning them, mmkay?

And what about combat? Well, the excitable looking semi-naked person running around the battlefield is probably so heavily protected that you're not realistically going to kill them with swords or arrows or anything short of siege weaponry. You might have some luck blinding them with smoke or paint or oil, or immobilising them with nets, or using some sort of chemical attacks on them... sprays of toxic or corrosive or burning liquids or powders might work, though it woudl be tricky to avoid your troops being harmed at the same time.

If you have warlocks too, have them trained up in unarmed combat styles... wrestling or jiujitsu, for example. Pin their counterparts down, try and get some breaks and dislocations going on. Try to find the gaps in the invisible armour and stick a dagger through it. You could try pouring noxious chemicals on them (acids, caustic agents, hot oils) but you'd have to be careful not to get any on you, too. Have someone bring a big chisel and mallet, and bash through the "armour" with brute force. Or best of all, have someone bring a bucket of water with them, and when you've got the enemy warlock pinned, stick his head in it. All the armour in the world isn't going to save you from drowning.

It occurs to me that there's actually a more entertaining solution to "how can you make the best armour using this magic", which is a sort of dalek/tank thing. I've been thinking that the warlock needs to be able to swing a weapon or at the very least wrestle, but actually you could "dress" your squire in a great big conical shell, with a couple of slots in the bottom for feet to stick out of, and one slightly offset firing slit at the front. Legs and arms are free to move inside the shell, but aside from the walking slots at the bottom can't reach beyond it.

The squire needs to be able to see the warlock so they can operate shutters on the feet or firing slits if they look like they might be in trouble, so there's a little peephole on a swivelling cupola at the top through which a telescope can poke.

The warlock carries a nice bow (long, composite or cross, your choice, doesn't really matter which) and maybe a spear. They shoot out through the slot (a bit of practise may be required to reliably shoot through an invisible gap, but in time they'll get it) and stick their feet through the ghost-holes in the bottom of the shell to move around. There isn't a reasonable way to hurt them, save via siege weaponry, but enemies could potentially lever up the edge of the cone and tip them over to at least stop them escaping whilst a big can-opener is sought.

The squire, at least, will be very safe under most circumstances, at least until someone starts using siege weapons on them.

Now all you have to consider is whether you could turn this into an invisible troop-carrying tank, by adding a door to the armour through which friendly troops could enter or exit...

• What if some squire wore a SCUBA tube? Would it work to block off the water? – he77789 Aug 14 at 11:49
• I hope you dont forget breathing holes. The squire needs to breathe but I assume the invisible armor on the Warlock blocks everything including air. This means breathing could be a problem. Additionally the "dont care about summer" sentiment wouldnt work as the air cant rush passed the skin due to the armor. So you would heat up anyway. – Demigan Aug 14 at 12:36
• @Demigan you can sit under a sunshade and not move. You won't heat up too much in that situation. Hell, you can have one of the other squires sloosh water down your neck to cool you down if needs be. Making a helmet airtight seems unnecessary, so I took it as read that it wasn't. – Starfish Prime Aug 14 at 13:05
• I meant that the armor would still overheat the warlock, and that the armor would also block airflow so both the squire and warlock would need the helmet to have air holes. If you made it airtight the poor Squire (and warlock) would be dead within half an hour. – Demigan Aug 14 at 14:01
• Well, so long as you’re pushing the concept to its outer limits, why stop at shutters and peepholes? Bolt the whole weapon on there! In principle there’s very little stopping you from building (most of) a crossbow straight into the armour and just carrying the bolts and any mechanisms that need riveting on post-ritual – Pingcode Aug 14 at 23:50

This would give warlocks a rather extreme advantage over regular opponents if little to no limits are placed on the magic:

Physics Get Really Messed Up With This

From the warlock's perspective the armor has no weight/mass, but to everything outside of the armor it does. As such if the warlock exerts any force on the armor from the inside it behaves like it weighs 0 kg while to someone on the outside they would feel the full weight.

This is combined with motion is relative. So not only do enemy attacks have their kinetic energy redirected to the squire, all the recoil of the warlock's attacks with their invisible armor would get transferred to the squire too.

No armor on bottom of boots

An example of this can be found in the boots. If the bottom of the boots are part of the armor then with every step the warlock takes the ground would exert force on the armor and thus cause the foot of the squire to kick up.

Since the feet are not typically considered vital areas (unless you are Achilles) warlocks will likely still have normal boots on with invisible armor on top of the boots. Not to mention finding a squire that can wear the warlock's boots would be annoying if said warlock had small feet.

Weight/mass as a siege weapon

I strongly recommend putting a limit on the weight or mass of the armor that a warlock can put on the squire. The reason for this is that an object tends to stay in motion until acted upon by another force.

Hypothetically a warlock could make a great shield a part of their armor but have it made out of materials that weight as much as whatever limit is set by the magic. Then said warlock could use the shield as a battering ram. To the warlock it weighs nothing and so accelerating it costs nothing more than how fast they can safely ram or swing it into a solid object. The squire meanwhile has the actual shield laying flat on the ground or braced against a boulder. The ground or boulder absorb the recoil while the opposing structure experiences getting hit by a massive object.

So in this scenario the warlock would be wearing light invisible armor with a very heavy shield. The soldiers and fellow knights would provide support while the warlock sieges the enemy's fortification and smashes into it.

Storing kinetic energy

If there are two warlocks present things get very interesting. If both warlocks have a solid metal mallet as part of their invisible armor with a good surface area they can store kinetic energy in the metal mallets using these easy steps:

• Have Squire A's mallet resting on top of Squire B's mallet
• Have Warlock B's invisible mallet rest on top of Squire A's mallet
• Put a heavy weight on the back side of Warlock A's invisible metal mallet
• Wait

Squire A's mallet will want to move up as gravity pulls the heavy weight down on Warlock A's invisible mallet. Fortunately for Squire A instead of getting slowly launched into space (assuming said weight is greater than the squire) it transfers the kinetic energy into Warlock B's invisible mallet. Which all of that force is then transferred into Squire B's mallet which in turn channels it back into Squire's A mallet which is still getting more energy from Warlock A. This would continue until the energy exceeds what the metal mallets can handle and then explode resulting in the death of everyone near by.

But, what if before that happened Squire A disconnected the mallet head from their armor and Warlock B turned off their spell? They now have an unguided projectile which could be used as a weapon if said mallets were placed facing a target they wanted to see gone.

Conclusion

As such combat in this invisible armor would likely exploit the physics loop holes introduced by the magic. As such I strongly advise putting a limit on how much kinetic energy can be transferred from the invisible armor to the real armor and a limit on how much mass can be treated as armor to prevent extreme loop hole abuse.

Even if there was reasonable limitations put on the magic, there is still one additional fun thing that can be done with it:

Powered Armor

Whether it is because the squire had a growth spurt and is now bigger than the warlock or the warlock does not want to risk their own life, the squire can wear properly fitted armor and go into combat while the warlock stays back and watches while wearing the invisible armor.

Flight

Make the squire's boots part of the magic armor and whenever they need a leg up or fly the warlock can simply stand up and the warlock's weight will cause the magic boots to be pushed into the ground (or the ground to be pushed into the boots depending on ones perspective) resulting in the squire getting boost or if the warlock weighs more than the squire with armor then flight. As the squire changes the orientation of their feet they would be able to change the direction of the boost to give them some control over it and thus give the squire mobility in combat.

Shield Recoil Countering

If the squire has a shield mounted to the armor then if they are about to block an opponents attack an assistant can smack the back of the warlock's invisible shield with a mallet. If done well the force of the mallet and the force of the enemy's attack would cancel out and allow the squire to keep going like nothing happened.

Also the warlock could flip their invisible shield upside down and put a weight on top of it that is about the same weight as the shield. As long as the squire holds the shield up vertically, they would be countering gravity's force on the shield making it less draining to carry around. Note since the shield still has mass the squire will still feel the full weight of the shield as they are moving, but if they tilt the shield in the direction they want to go, the shield should drag them in the direction they want to go.

Powered strength

Lastly a squire could do a similar siege weapon style smash that the warlock did with their shield. The difference is that the squire leans their shield, mallet, or reinforced gauntlet against whatever they want pushed. Then the warlock with some assistance puts heavy weights or strikes the back of the invisible armor causing the squire's armor to push into the target without the squire doing anything.

If the warlock rests a heavy weight on the back of their invisible gauntlets then the squire's gauntlets will want to move as if they had a similar weight behind them. Thus the squire could grab something of similar weight with the gauntlets and lift it similar to how Link from The Legend of Zelda does with the Golden Gauntlets. While not in use the squire would want to clasp the gloves together so the force on the gloves would cancel each other out (doing the reverse would be very bad).

• As an extension of your hammer trick: stack any block of material on top of its invisible partner, and (with a nudge in the right direction) you have a self-propelled projectile. – MJ713 Aug 15 at 3:34
• The reason that conservation-of-energy is being violated is that the visible armor is pulling "double-duty": it "accepts" the forces applied to the invisible armor, yet it also acts like ordinary matter by "accepting" the forces applied to it directly. If we make it so that the armors trade forces, i.e. forces exerted on invisible armor are experienced by visible armor, and vice versa, then it prevents the hammer scenario. But I can't figure out how to do that without losing the invisible armor's weightlessness... – MJ713 Aug 15 at 3:43
• Note some parts of my answer have become OBE by updates to the question. I will update it later to remove said portions. – Anketam Aug 15 at 11:25
• I'm loving the suggestions for getting some symmetry out of an inherently asymmetric interaction :-) – Stephen Aug 15 at 12:31
• I'm not sure that's how the armor works. If it is, then I'm going to counter your citation of newton's first law, with newton's third law. For every action, there is an equal and opposite reaction., aaaaaand it suddenly all falls apart at the seams. Either the warlock becomes very bouncy, or there is no actual mass there. – tuskiomi Aug 20 at 18:32

Uh oh, I'm going to drop an NSFW link... lol jk it's not that NSFW.

So, as you've probably heard, back in the good old days, barbarian fighters among Celtic tribes would get naked and (in the case of the Picts) paint themselves in various colors to seek blessings from their gods as well as scare the enemy. Plus, these peoples were very warlike - they treated their open wounds as scars of pride and would only get angrier as they fought. This also meant that they were more vulnerable to any kind of weapon, but maybe slightly less vulnerable to infections caused be contact with contaminated clothing.

Now, your warlock will not get hurt in combat given that he/she has the necessary armour on a squire, to basically no consequences unless the squire gets hurt, in which case suddenly this guy is a sitting duck to basically any kind of melee/ranged weapon. So here's a few cases that I can think of:

1. Glass cannon: Your warlock is a Celtic BAMF. So, instead of wearing anything at all, this guy goes into combat fully naked. If he can use paint to scare off his/her enemies, he wears that. If he can paint runes/other magical incantations onto his/her body (not just for protection) he can do that. He can also create weapons/minions out of his/her own body like Momo Yaoyorozu from My Hero Academia (not sure if this applies in the universe you're building, and Momo can't make minions like that), in which case having the maximum amount of your body exposed really helps.
2. False Knight: As we all know, Knights are beefcakes. They wear heavy armour, use heavy weapons, ride a heavy horse, etc. And as you mentioned in your comment, if the armour on the warlock's squire is bulky, this will also affect the warlock when folding his/her arms, etc. This means that (if I understand correctly) arrows will bounce off the armour, which would be maybe a few centimeters off the bare skin of the warlock. So, to trick the enemy, we could dress the warlock up some more - give the guy a fake/light version of a knight's armour on top his/her own naked body which is protected by the armour the squire is wearing. This isn't for the warlock's protection, but to confuse the enemy and trap them into thinking they're fighting a knight, when the reality is much worse.

I hope this helps - I'll add more ideas if/when I have them!

• Now I am visualizing a bunch of buck naked warlocks doing this while their squires wear super-padded nonsensically thick armor. So thanks for that. – Kevin Aug 15 at 0:33
• I like the subterfuge. Combined with the unreasonably hardened proxy armor, this would be the ultimate foot knight. – Joshua Aug 17 at 3:04

If the squire dies, the bond is broken and the warlock is left in the middle of the battlefield with no armour at all

Pain has the advantage of signaling when a part of our body is being overloaded, in the broader meaning of the term: if you get a strong hit on your arm, pain there will point you at avoiding further contacts, to prevent critical failures.

This sort of armor sounds like the worse version of taking painkillers with an injury to continue playing. It can be lethal for both warlock and squire!

What armour and combat techniques would these fighters develop to maximise their advantage from this ability? How much of an advantage would it give them over ordinary combatants?

Any tactic they use, they must aim at reducing the taken hits: if the warlock has no awareness that the squire is comatose after a head blow, getting other head blows will leave him naked on the battlefield with no warning.

At the end, the warlock will only benefit from the pain insensitivity as much as he can remain conscious of the taken hits: he will still need to protect his vital parts (abdomen, head) since a blow there can be lethal, while he can go easier on blows addressed to the limbs (a blow on the kneecap is painful and incapacitating for whoever gets it, but hardly immediately lethal)

One thing you could do is to make the armor a several foot thick steel sphere that the squire wears/sits inside. The warlock wouldn't be able to use weapons easily as the invisible armor would extend most if not all the way to the end of his arms and completely cover him.

The warlocks tactics would then be to just run and body-check his enemies and crush them under the several tons of steel.

The most difficult part would be transporting the armor. It would need to be transported by cart and would need a pulley system to lower it onto the squire before battle and then be lifted off if him.

Deception

Since the knight doesn't look like a fully-armored knight, he gains greatest advantage from surprise. Scouting, raids, infiltration-and-fomenting-intrigue, etc.

Pitched battles seem a lousy place for (apparently) unarmored folk, and the knight gains little advantage from his additional mobility - the rest of his formation is unchanged, and they fight together. Once the secret is known, the enemy will start putting crossbow bolts through unarmored-folks-on-horses...or capturing them.

Starfish Prime has a very complete answer, but the following might help you deal with these monsters.

With no limit on strenght on the armour, you will need other ways then brute force to deal with these.

To deal with the Warlock-knight:

1. Use paint to make the invisible seen.
2. Use nets, wires, bogs and marches to snare the unstoppable.
3. Use time to starve the unhurtable.
4. Use poison or water to end the unbreakable.

To deal with the Squire:

1. Use poison to stop the poor lad.
2. Bribe the lad to not don the complete the armour.
3. Bribe the lad to not wear armour at all. (Use of fair maidens are recommended)
4. Bribe the card driver to drive a knife in the lads soft parts.

Warfare would be... funny. Hear me out.

It's established that the warlock could not wear any armour, as long as the squire does. If the squire is killed, the warlock is unprotected. But there are no restrictions on how much armour one can use. So, let's assume we get a full plate armour. There are still some places where it could be pierced, if the attacker is lucky or knows about your trick. Armour can still be bludgeoned and deformed, which could be problematic - especially if you hit the head.

Now, we can just add more armour, after all, all the squire has to do is just wear it, as long as he's actually wearing it, it counts. In which case, why not just a multi-layered block of steel, wool and other materials, to create a wearable block of invincibility that would protect the squire from bludgeoning? If the block is big enough, you're also safe from piercing weapons. Pikes are likely the weapon with the most reach, and thus potentially the one that could pierce the furthest (assuming you can pierce and shove the shaft through the box-armour). Let's say that for some reason someone has a 5 meter pike. Well, just make the box-armour have a length from outer plate to beggining of center core (the space that the squire inhabits) measure more than 5 meters.

You're essentially impervious to any weapon, other than fire. It's still possible that the fire harms you, due to the heat and possibility of asphyxiation. However, since the only thing that can catch on fire is the outside of the magic part of the box-armour, the warlock will have a bit of separation between him and the flames. Plus, now you're literally walking and fire is moving around you. If that doesn't scare your enemies, what does?

So, now that we established how someone could make himself impervious to death in battle, how would said battle play out? Well, with the given constraints, we can deduce that, even though the armour's weight wouldn't affect you... it affects others. This is where it gets interesting.

Let's say that the box-armour has at least a 5x5x1 meter plate of carbon steel per side. That's (just on that single plate) an approximate weight of over a a tonne. Now, a box has 6 sides, so multiply that by 6. Just to put it into context, that's heavier than a Cadillac Escalade.

Now, run towards someone. You're at the very least knocking them down. And when you do, jump. Aaaaand they're crushed.

Or, if the warlock wants to be particularly nasty, he adds spikes to the box-armour. In fact, You run towards someone, and suddenly there's a hole in the middle of his chest, sure, your spikes may break if you run towards a particularly well defended opponent (for example, his armour deflected the spike, and your spike broke), but hey, you can crush him anyway. But assuming that you pierce his armour, he's dead. Then he turns to the right and that person's torso is ripped apart, because the pike actually has serrated blades on its side. Hey, if it doesn't weight anything on the warlock... Just look at the other troops' face in horror. Heck, you kill one person and the rest routs.

The warlock doesn't need a weapon, he is an armoured tank with the mobility of a human.

Eventually someone somehow will remember to try using catapults or cannons (or shells, depending on your world) to hit the warlock. It could be problematic, if the armour isn't adapted to withstand these shocks. Again, remember, as long as the squire wears it, it's an armour. Add more layers to withstand such impacts. Perhaps one of the layers could be water or even mud to dissipate such ammounts of energy. The warlock only needs to remember one thing, as long as the squire wears it... it's.. hold on.

See, that is when the warlock realized something. Dig the squire a deep grave, put a straw on his mouth and lay him there. If he's wearing any sort of gambison, he's armoured... and the dirt is.. another layer... and.. then there are more...

Yes dear reader, the warlock realized he could walk with the fucking mass of the planet

How would warfare change? It would end. You can't defeat something that if it jumps, it cracks the planet in half. In the end, that's what would ultimately happen. And eventually the warlock would become his own planet.

• This! Was about to propose entombing squire in concrete armour, but wearing fucking planet sounds even better! – internetofmine Aug 16 at 5:46

Squires and their warlocks would need to be close to the same shape. This would discourage the use of young, still-growing squires. It would also cause the squires and warlocks to have matched training regimens and similar diets, so that you don't have one become fat while the other either bulks up or starves.

The squires would need to be kept in a defended, sheltered, rear area. If the enemy can reach them, they would be vulnerable. (The armor they wear is protecting the warlocks, not the squires.) If the enemy can manage to lob exploding artillery or Greek fire at the squires, the effect would be devastating.

One of my favorite books, Paladin of Souls by Lois McMaster Bujold, had a scene where one character's injuries were being "passed off" to two other characters. The one "passing off injuries", a great warrior, was sent sneaking into the enemy army's camp. The two "injury receiving" characters were safe, laying in the castle, with attendants at hand to bind wounds as they occurred. I would describe it in more detail, but I would rather not spoil it, as it's a fairly epic part of a great book.

How it could be applied:

Using this as a model (including genders), I would expect combat to go like this:

Pre-battle:

• Warlock prepares for battle by doing some stretches, swinging his sword a few times, etc.
• Squire prepares for battle by donning armor, retreating to the tower where attendants will have a good view of the battle. She will get strapped to a table or the floor, or maybe the armor is heavy enough to hold her down.
• Warlock heads out to battle. Not fearless, but knowing he will be well-defended. While he's out...

Case 1: Warlock gets hit with an attack that the armor can handle.

• For the Warlock, conservation-of-energy and conservation-of-momentum kick in. I would expect the armor to "feel" what it could from the impact, then have the rest of the momentum (and remaining energy) transfer back to the Warlock, i.e. he could be knocked down by a strong enough hit. Impacting on the ground would also be transferred partly to the armor, and then back to the warlock.
• The squire, in the meantime, is jostled as the armor she is wearing seems to be hit out of nowhere. Because she is tied down, it doesn't do a whole lot, otherwise.

Case 2: Warlock gets hit with an attack that damages the armor some.

• Warlock says "ow", among other things. If he has been hurt, I imagine him to either retreat or keep fighting in an epic way. If he has not been hurt, he will try to avoid being hit in the same spot, knowing he has a weakness there.
• Squire and attendants notice the armor get damaged. Squire is probably a bit shaken, but otherwise still unharmed. If the armor looks repairable, the attendants get to work right away, forming new material onto the armor to cover/reinforce the hole/break.
• An extension of this idea: If the armor was optimized to be swapped out in segments, the attendants might watch for a moment when the warlock is safe, then swap a damaged segment of armor out for a new piece, pit-crew style. This would be another reason the warlock would try to not be hit in the same place - he might have a moment of no armor, with knowledge that more armor was on the way.

Case 3: Warlock gets hit with an attack the damages the armor a lot. (Like, somewhat crushed, or maybe cleaved)

• The squire very likely would be injured by the deformation of the armor. If she's still alive, she probably says "ow", and she and the attendants will get her into new armor as quickly as possible, assuming it's safe for the warlock. If she's not alive, the attendants will either put her in new armor (on the off-chance she's actually just unconscious) or carefully remove her body from the twisted wreckage and begin preparing her for funeral rites, knowing they've done their best to help the warlock.
• The Warlock will definitely say "ow", if he's not dead from the blow. A crushing blow would impact hard, a cleaving blow would probably cleave him, too. This isn't to say he can't have awesome "block it with his arm" moments, but a heavy-duty mace or axe (or siege weapon) might make him hesitate.
• If the Warlock's not dead, he'll be checking himself for armor as an indicator of his squire's life. Whether or not she's alive, he'll be retreating hastily - either because he now has no armor, or because the squire needs a chance to swap armor.

Odd circumstance: Warlock dies, squire does not. (e.g. stabbed with a Rondel dagger)

• If the Warlock dies and the Squire does not, what happens is dependent on the nature of the spell.
• If the magic persists after the warlock's life ends, the squire and attendants may not even know he's dead unless they see him. This would leave the squire in danger of being hurt through the warlock's body, lying on the battle field. (If they see him dead, I think they would then get the squire out of the armor very quickly.) However, this circumstance begs the question, would that Warlock then always be connected to any armor the squire would wear? "Capture the warlock's body! If you ever feel armor on that body again, attack it!" Or crush it slightly to slowly hurt the squire...long-distance torture? The squire would likely never want to be in armor again.
• If the magic ends with the Warlock's death, the attendants and squire may sit there for quite some time, trying to figure out if the Warlock is dead, or if he simply retreated.

• The situation is not as extreme (or hilarious) as other answers describe. Perhaps the spell has only been recently discovered, does not have widespread use, is "forbidden, dark magic" that many dare not try, or has other limitations that prevent the use of non-traditional armor.
• The armor is traditional full-plate or equivalent, except maybe more modular (for swapping segments out quickly).
• The squire and warlock are working from a castle, keep, or other fortified location. One could instead sequester the squire where she could not be found by the enemy for the battle's duration. Per a comment I greatly agree with,

I think there would be a LOT of assassination of squires. – 23fc9a62-56de-47fb-97b4-737890

• so the squire would be protected somehow. Maybe that squire is also a warlock with a separate squire...share the damage? Or maybe Squire 1's armor would make the Warlock's armor not 'quite close' enough to the skin, thus avoiding another possible extreme of extensive-spell-armor-chaining.
• A warlock and squire in battle are the exception, not the rule. (This means that armies don't expect a warlock, and might not know the best way to deal with one. If they did expect them, this answer would also need to cover how armies would counter them, such as specific combatants with heavy-duty maces for "crushing squires via warlocks".)

As a final note, I do not disagree with the other answers. I think they are awesome and deserve the upvotes they got. I just think this view provides a less extreme (though perhaps less interesting) option.

With all the good ideas here, only one had the idea of multiple layers of differing materials, and I'd like to expand on that with my own ideas.

Armor would be considerably different than it is today. It wouldn't necessarily have to be feet thick, but it would be layered differently. Real knights metal armor is generally a single piece of metal in a specific shape and only overlaps where there's a joint to protect.

With offloading the weight and most of the cumbersomeness, you can get some really interesting layering going on. You'll probably want metal skining both the inside and outsides of the armor, but you can have wood layers that are cross grained to not only absorb some impact, but also grab and hold a pike/ spike, or arrow. You can also add more soft padding between the layers to avoid impacts better.

Metal is great at taking a blunt force, but it can be cut somewhat easily, so you put that on the outside. Wood can defend against cutting forces really well when it's against the grain, but breaks when hammered, so you have a layer of wood with vertical grain, another with horizontal grain, and maybe another layer or two with diagonal grain. Metal stretches/deforms before it breaks/tears/cuts, so having another layer on the inside would protect against anything that somehow makes it through all of that.

If you sandwich all of that together solidly, the wood still takes the force of the beatings and can break, reducing their sharps stopping power. Since we don't have any encumbering the knight or weighting them down, we can add even more layers. Put cotton, hay, horse hair, cloth, or other bits of padding between all the layers of the armor. We can also make the layers plenty thick. We still probably don't need feet of armor, but 1-2 inches per layer is plenty. You still need to be able to move the armor when not on the battlefield, and the bigger and heavier it is, the more likely it's going to fall behind the army and less likely to be part of an ambush, raid, or incidental battle. Also, 10 layers of 1 inch thick materials is still 10 inches thick total, which is something like 120 times thicker than real knights armor.

You also have to consider the quality and quantity of the roads during that time. Most battles weren't directly on a trade route, so wheels would have to be able to get over rough ground with moderate ease.

Also, the larger the armor, the more oxen, horses, animals in general needed to pull them. This means a more massive supply train. As the saying goes, "An army marches on its stomach". A large army already has a pretty good sized need for food, water, shelter, and more. Adding to this has diminishing returns. If you can't afford to take your super-massive-overly-armored knights to a battle because their armor is the size of a castle, then you aren't doing yourself a favor by having them.

You also have to consider the amount and what types of materials that can be sourced. Stone can be found easily (hence large castles), but it is susceptible to breakage. It can't be repaired like metals, nor can it be easily replaced on the hoof like wood. It's also geared more towards compression, rather than striking or sharp forces. You can gently put a ton of material on a rock and it'll be fine. Drop 100 lbs on it and it's rubble. Use a chisel on it with a 5 lb. hammer and it's split in two.