Why would giant mechs use melee weapons?

Question

Mechs are really just giant usually bipedal walking tin cans with their human pilot inside. I mean, shoot the legs and they can't move much anymore. Not really realistic.

Regardless, in a futuristic world where for some reason mechs are the main fighting forces supported by infantry and air forces, why would the mechs ever use melee weapons to fight other mechs? I have seen and read a few novels and games where they have mechs where a melee weapon[chainsaw, giant sword, lightsabers etc etc etc] was prominently used instead of a ranged weapon.

Like the reason to have mechs would be to act as giant walking artillery units right? They need to be big to carry their equally big weapons to shoot far and destroy their enemies and even if the distance minimized, I'm sure charging at a giant mech which has two miniguns, a plasma cannon, lasers and enough rockets to raze an island with a melee weapon is a really bad idea.

To summarize, what kinda reason or situation would mechs have to use a melee weapon to engage another mech?

They kinda look like this, hopefully with arms if they are using melee weapons.

Answer 1

As far as we know IRL, mech fights will not be good way to wage a war, so this answer is meant more as an excuse for the writer, not the actual reasons. That said...

Limited ammo.

Sword would weight about the same as two, three rockets? But with it, you could destroy more than three enemy mechs, if you are a good enough pilot.

This does not make sense if you are close to your supply lines and your nation's resources are not limited. But guided missiles can cost millions of USD. Literally. Thousands is pretty normal, if not cheap. Even unguided rockets are expensive. For the cost of few reloads, you could get one more mech. And of course you would need either transport mechs to bring rockets to your line, or maintain non-mech supply lines. These would be pretty hard to defend. Tanks, using non-rocket missiles, can carry more ammo, but they are low and can withstand a lot of recoil. Mechs, as high bipedals, cannot. So no large ammo storage for them, and no cheap ammo for them.

Even if you can afford to make and deliver enough rockets, it won't work for special units you would drop behind an enemy's back. And you sure want some of these, for strategically critical missions. These missions may be suicidal, but that's the duty sometimes.

Urban war

In dense urban areas, you don't see an opponent until he is one or two blocks away. For a mech, this is a few steps' distance, and at such a close distance a sword can be more efficient. The time needed to slash is shorter than the time needed to aim a gun. And with a gun, if you miss you are destroying infrastructure your side will need, a problem which is nonexistent for swords.

Answer 2

Shield Technology

Technology exists that can protect against small projectile weapons, but not against the much larger force and energy that comes with the swing of a melee weapon(as in Frank Herbert's Dune).

For instance, a mech could be protected by auto-guided lasers that can vaporize small things like rockets and bullets before impact. Or, there's some type of surrounding magnetic braking system that slows bullets down to a speed where they can't hurt the mech. Only A melee weapon swung by another mech would have the energy needed to make it through the magnetic field.

Hence, it would be necessary to outfit the mechs with large, sturdy melee weapons to destroy each other with.

Answer 3

Why would giant Mechs use melee weapons?

Actually my answer is more for this question "Why using giant Mechs in the first place?"

Answer: Demoralisation

The party that uses the Mechs instead of conventional weapons has high advanced tech and wants to show it. Their Mechs are so advanced, that they can easily compete with Tanks of other parties and outperform them.

Everyone knows how dangerous these things are. With the height of a small building they can be seen and more important, better identified than tanks.

The tactic is to lower the morale of the enemy. Taking advantage of the fact that you are there and everyone knows it.

Now we come to the part why using melee weapons

The Mechs should be able to get in close range to their target in a short amount of time. The longer that will take the more hits it needs to evade or absorb before doing anything. Actually I don't know how good tanks are in close combat, but I assume that they perform not as well as on distance. Everything that explodes would also harm the tank. Maybe the turret can't aim at the Mech because it is too close. The inability to attack the enemy with full efficiency could have an even more demoralizing effect.

So the reason to use mechs is not because they are better in combat, but to strike fear to your enemies. You could make the mechs bigger than trees and houses. So advancing enemies will definitely see them when they stand up in the woods.

In the end the mechs exists to prevent fighting in the first place. No one wants to fight the mech.

Answer 4

Serious radar jamming technology

Take a note out of Gundam, one of the pioneers of the giant mecha genre. Wanting to write a plausible humongous mecha story but realizing that giant humanoid combat robots are pointless and impractical, the author created a world where a newly discovered particle made radar jamming easy, rendering long-range weapons useless against mobile enemies. Also I think it made problems for delicate equipment and computers. So human-piloted humanoid mecha fighting with melee weapons made sense.

Answer 5

Fight The Enemy, Not Your Weapons

The leading responses are all assuming an enemy similarly equipped, with similar tactics, when it is clear that asymmetric warfare is the most common sort of conflict. The only reason to use a mech with a melee weapon - or indeed a mech at all - is if that is the ideal weapon for the enemy you're facing.

Such an enemy would be one that is most easily countered by a larger-than-life metal humanoid with melee weapons. These enemies would include ones who are easily intimidated by size, who are numerous enough that ammunition is a problem, who are embedded enough that supply lines are a problem, or who are constructed in such a way that projectile weapons are insufficient or inefficient (how many .50 caliber rounds does it take to stop a triceratops?)

Note that while sticking artillery on a mecha seems 'a natural step', it's not necessarily the case that artillery is needed for the enemy at hand. If the mecha is primarily a sensor platform, for instance, which must be mobile over a variety of terrain but doesn't usually partake in combat. Or, the artillery in question is so long range (such as surface to space artillery) that using it in direct combat is impractical, then backup weapons are preferable which are, in turn, geared towards the sort of combat you're likely to face. Which brings us to...

Equip For The Job At Hand

About this image, ask yourself: why didn't they just use rockets? Contrary to a lot of answers here, urban warfare may be exactly why you want a mech with 'melee' weapons not because you protect the environment but because you are more dangerous to the environment. The ability to, on a rolling basis, demolish some or all of the environment you're in is a large tactical advantage. Such 'combat engineer mecha' can reduce enemy entrenchments and build your own while being protected against unexpected (or expected) attack. In this case the enemy is buildings, or open fields that need ditches, and the melee weapon (read: 'fancy shovel') is the best thing for the job.

While it is a narrow set of circumstances where a large, bipedal mechanized humanoid is the best weapon of choice, should you also need a tool for your mecha for jobs such as destroying buildings or entrenching open ground, we can assume that pilots will quickly learn to use that tool to squash endless waves of mimics - you know, should they need to.

Likewise, if the requirement is that the pilot is armored and unsupported for long periods over treacherous terrain, mecha may present a better option than, say, helicopters or other high-fuel devices or tanks with their reliance on some form of flatish ground. (Obviously there are different problems: the ability of the ground to support the mecha, etc. etc.)

Be Aware of Your Environment

Is the cargo loader from Aliens the ideal mechanized combat instrument? No. But is it an effective one? Yes. Why? First, it equalizes the disadvantages the human has: provides armor, size and strength against an opponent that is larger, stronger and has blades. Secondly, and most importantly, it doesn't risk turning the environment against the humans. In this case, the environment is a space ship that, if breached, will mean defeat. Rockets and projectiles in this situation are exactly the wrong sort of weapon - for the same reason the marines should have avoided using firearms when underneath the main cooling tower for the nuclear reactor.

In any situation where targets in the 'background' present a very high risk should they be inadvertently damaged, one must choose a weapon that reduces the chance of that happening. Space is one such environment: not only do bullets and rockets whizzing around often defeat the purpose of destroying your enemy, but due to Newton's Third Law (and indeed, the other two) shooting a bullet means you're forever accepting an equal and opposite trajectory (I'm eliding the actual physics here). Swinging an axe presents a different but more easily managed physics problem.

Be In Control of Your Equipment

While it has been mentioned that projectiles can be stopped or confused in several other answers, this concept has not been abstracted to the general case: while that bullet/rocket/rock currently arcing towards your target might be 'yours', it is only that way so long as no one else messes with it.

In a world comprised of EMPs, hacking, shields and other mishagus, once an object leaves your orbit of control you can't truly count on it being 'yours'. (And, notably, combat lasers and other 'beam' weapons might be prohibitively hard to make work, so 'instant hit' weaponry may not be on the table.) The nice thing about using a weapon physically attached your vehicle is that you are in direct control of it: if you lose that control you've already lost control of your vehicle, which is the far worse problem. The hardened electronics, active EW and black ice that is cost-effective for your vehicle but not for your rocketry can also protect a melee weapon. And, for that matter, in a super-high-tech environment, 'dumb' weapons generally need less protection (even if they are riskier).

Answer 6

Same reason knights in medieval battles carried daggers;

As a backup weapon, and for utility.

Battlefields are unpredictable, and no soldier will want to go into a situation where they might have to fight against someone who will have a total advantage. Imagine trying to direct ungainly arm/weapon pods of a mech while ducking and weaving at an enemy whose only a few feet away from you and doesn't have that limitation.

Molot makes good points about ammo conservation and the cost of shooting things, but if you're going to build mechs anyways, I feel cost can't be TOO much in the forefront of your mind.

An enemy mech that is melee equipped only has to swing his arm in your general direction when engaged at that range. If you get hit, even if it doesn't do much actual damage, your knocked about; your facing is probably changed, and your mech might very well end up on its butt and out of the fight. And, as with knights, someone quick and with a dagger was a real danger; they could get around you and shove it into one of the weak points of your armor quicker than you could turn to face them (especially) if you were bogged down in the terrain and they were not.

Melee weapons grow in effectiveness if the ranged weapons (guns, lasers, missiles) require multiple hits to penetrate/kill. The longer it takes to down the other person, the more chance they have to close that distance and knock you off target.

These type of encounters WILL happen in a limited visibility environment if both sides employ high mobility mechs; cities, fog banks, dust and rain storms. This is more endemic of warrior style combat then soldier style, where individuals and small groups engage without support, but is perfectly reasonable for commando style fights.

Another major factor is the utility of melee weapons for mechs. Maybe your “sword” is in reality a giant shovel; its main job is to dig trenches and help construct a forward operating base. Even current soldiers digging tools (E-Tools) can in an emergency double as a melee weapon. Knights used their daggers off the battle fields for various tasks, including to eat with, and while probably not ever expecting to have to use them on the battlefield, took them anyways because “just in case”.

Answer 7

Momentum

If mechs have extremely strong armor then you need to deal extreme damage. You can't kill an elephant by pocking him one thousand times.

You need a ram (call it a spear to sound more noble) with the momentum of a mech behind. This will have much more momentum or kinetic energy that any kind of bullet or rocket.

To be a bit more scientific, there are mostly 2 reasons a ram can deliver more impact than a kinetic missile:

delocalized burner

A rocket can only deliver as much kinetic energy that it can afford to burn in its travel time. If this power gets too high, the engine burn or melt. Same problem with a cannon.

The engine of a mech has the same constraint, but it has one engine for each joint and can afford a complex cooling system. Hence a mech can cool MUCH faster and can produce more energy over any given time.

Aerodynamics

Aerodynamics is on the melee weapon's side (maybe on the rocket's, but certainly not on the bullet's)

To deal extreme damage, a missile needs to reach extreme speed... but then have to face extreme air resistance.

A very large mass with a lesser speed does not have this problem.
A 100kg Warhammer slashing at 200 m/s is possibly more realistic than a 500g bullet at 2800 m/s (10 000 km/h) and would have the same kinetic energy.

And a 10t mech need only 20m/s to reach the same energy.

You can increase this by setting your story on a high density atmosphere or even under water.

Answer 8

Can I recommend the Battletech universe as a reference? The entire system there revolves around mechs of one form or other. The major reason for using mechs in melee fights was that they weren't battlemechs. Many common mechs were construction, lumber or transport mechs, which wwere retrofitted for combat. So, lumber mechs had their chainsaws, construction mechs had mechanized hammers and so forth.
The actual battlemechs had no melee weapons, whatsoever.

However, I can think of a couple of tactical needs for bothering with melee weapons. As I pointed out in my earlier comment, any sort of interference with sensors, with some sort of terrain obstruction--be it fog or a steep mountain would mean you can't see the enemy till they're right on top of you. Since the sensors don't work, you can't risk sending tanks into the fog for fear they'll get stuck, unless somebody opens up a hatch in order to guide the vehicle--and then they'll be sitting ducks. That's when you send in mechs armed for melee combat. The mechs can cover any kind of uneven terrain better than a wheeled or tracked vehicle can, the transparent visor means the pilot can see where it's going without having to pop their head out. And most importantly, if they do see an enemy vehicle or mech, since they'll be right on top of them, they can respond immediately, without having to fall back in order to aim.

Answer 9

Because you want to rattle that squishy human INSIDE the mech without damaging the mech too much.

It seems highly unlikely that a mech sized mace, axe, or hammer would pack more punch than a laser, PPC, gauss rifle, missile, or whatever ranged weapons it is using. But what a good thump with a chuck of steel is going to do is shake the crap out of the chassis, possibly stunning or outright killing the pilot inside without trashing the mech itself. Might knock loose some circuit boards, bust hydraulic seals, or the like which will also reduce the mechs operational efficiency without completely destroying it.

Or, conversely, smashing exterior weapons or limbs can disarm the mech without destroying the (presumably) more valuable central control systems and perhaps even allowing the pilot to survive, to be ransomed later. Otherwise all you are doing is lobbing high explosives at each other, probably with all sorts of toxic byproducts (just read up on what happens to a tank hit by a depleted uranium sabot round, or that had DU containing chobham armor).

The fundamentals of mech combat, at least in popular fiction like Battletech, assume a general withdrawal from the "total war" philosophy of killing your opponent by any means necessary and a return to a more, for lack of a better term, "gentlemanly sportsman-like" code of combat that allows for big fat high value targets to tromp around like the aristocracy of old, secure in the knowledge that if they fall in battle their personal safety is somewhat guaranteed. Plus factions wouldn't devote their entire economies into the war effort, so salvage and conserving fighting equipment would be paramount. Simply blasting your opponent into radioactive rubble might win you the battle, but lose you the war because now you have no way to salvage equipment to resupply yourself, make money to pay for your troops, and get hostages to exchange for your own/ransom off. Under these conditions, melee weapons make sense as a way to reduce lethality on the battlefield (at least for the mechwarriors, who are the only ones anyone cares about anyway).

Answer 10

Bad sensors

Range weapons require you to be able to accurately detect the location of your opponent in real time and have weapons able to hit him.

You could have situations were sensors are easy to jam or that there is snow or ash falling that blocks sight more than a few yards away. Frequent use of emp would kill sensors as well, so if you have to wait till a foe is a few dozen yards away you might as well use melee weapons.

Unstable platform

A biped walker is much more unstable when walking than a tracked or wheeled vehicle, this will make the weapons they fire less accurate at range, again encouraging close range.

Durability

Humans are odd if you punch a thumb-sized hole basically anywhere in them they can bleed out and die quickly without treatment. But a mech could survive dozens of holes in limbs and keep fighting, it could have valves to cut off the flow of oil or electricity to damaged sections and so survive and keep fighting despite the loss of 3 limbs. It would be hard to dismember a mech completely enough at a distance to take it out of the fight (basically punch small holes in it till it stops working). It might be faster to attack it in melee (cut large slashes in it) (especially if you have lightsabers) Robots survive better than humans if small holes are punched into them so gunfire might not be the best way to destroy them.

Answer 11

Why do humans that carry a machine gun still carry a knife, a sword like in japan, or an axe like the Indians and vikings did.

I'd say as many already have ammunition. It can run out, it weights a ton.

But the foremost reason I'd use a melee weapon in combat over high explosives, nuclear bombs, Plasma bombs and other explosive devices including mines is proximity and precision.

Do you really want a nuclear bomb to go off near you even if you have centimeters thick composite armour when another mach stands near you? No you take your knife and find the weak spot in the armour.

Personally I would like a spiked club that is electrified. he he

Answer 12

Extreme close quarters combat. I'd note a 'traditional' mace or axe would be a pretty terrible weapon on this situation. A Jackhammer the size of a small truck on the other hand, might be more useful in short range combat. Unlike a gun, you can power this off the same power supply as the mech itself, and it would be useful for combat engineer type work, demolishing and building fortifications and so on. After all, hitting someone in the head till they stop moving is a valid combat tactic.

Likewise a high speed spinning blade might make more sense than a sword. A sword against armour might stop. A high speed blade would slice through.

And similar weapons are in use in robot fighting tournaments, so you might have a 'in universe' explaination of pilots being familiar with such weapons - you'd have 'military' mechs with mainly energy and projectile weapons and 'gladiatorial' mechs that combine top notch pilots with limited armaments and physical weapons.

Answer 13

There's one thing that hasn't been mentioned, and I think it's a very salient point here.

CULTURE

In the West, we have this notion of the weapon as being a tool to be used and then thrown away and replaced when no longer useful (the culture of the gun) This gives the every-man a chance to stand up for his liberties and, in the case of the American Revolution, allowed a previously occupied colony to break free of its imperial masters and strike out on its own.

In the East, however, they have much more of a focus of the weapon being an extension of the self. (Samurai Culture) This sort of weapon is generally always something that is either close combat, or in the rare-case of guns, then they're arm-cannons like Megaman and Samus Aran. These types of weapons take years to learn and many lifetimes to master fully. In the Sengoku Jidai (Warring states period) you had whole clans of Samurai, many who were descendants of Samurai themselves fighting it out for the title of Shogun.

So when it comes to mechs, things like Gundam and NeonGenesis, which have their origins in the East have a much higher focus on melee weapons in their arsenal as that is the culture that that country is based off.

EDIT - Thanks TechZen for the great point in your comment as added below:

Actually there is little difference in the "Cult of the Sword" across world cultures. Medieval western warrior classes where every bit as mystical about swords as Samurai. Weapons become identity when an individuals status and general role in society depends solely on their ability to fight. The horrific reality of being trained from toddlerhood to kill, and belonging to social class were everyone else is a killer as well, creates a need to justify killing and that leads to the mystical veneration of killing tools as being something more spiritual, serving a great good. – TechZen 15 mins ago

Answer 14

Pure Intimidation

As Howard Taylor said in his review of Pacific Rim:

... every technological advance necessary to create a walking mech will be obviated by better uses of that advance. As my friend Dave put it so brilliantly several years ago, (and I paraphrase) "If your tech is so superior that you can get away with giant killer robots, the only reason to use them is for sheer intimidation. This means that what you should be building is giant killer robot clowns."

What's more intimidating: a gun, or a massive sword? There's something just psychologically terrifying about a sharp blade in close quarters. Sure, we all know a gun can kill us... but a blade can HURT us - and we know that at the level of our brain that raises the hair on the back of our neck. Aim for the primal hind-brain and intimidate it: hit someone hard enough they either cannot or will not come after you... and fear is a good way of getting to the latter.

... although now I want to see a movie with giant sword-wielding killer robot clowns.

Answer 15

Consider this: The world is a changed place. Warfare is mechanised, and sending humans to the slaughter, to "die for their country" is no longer done - people don't stand for it any more. Battles take place between civilised organisations or even corporations, and civilian casualties or "collateral damage" is no longer considered acceptable. People no longer buy into the psychology and politics of hate, nationalism, or religious extremism.

But battles still take place. The belligerents are powerful enough that governments are not able or willing to stop them, but not powerful enough that if they started killing people and destroying hospitals, orphanages and kitten sanctuaries, that they would get away with it.

And battles still rage within urban areas. Now how do you approach it? You can't just start lobbing missiles and shells around because you might miss and turn the city into a wasteland. Instead, you have large lumbering mechs, armed with large melee weapons made of highly advanced pneumatics and technologium - a metal composite that is so hard and sharp that it can cut through enemy armour, buildings and machinery without damage to itself. And with no chance of stray missiles or big explosions, it minimises the risk of killing innocent bystanders.

Perhaps the weapon can also be electrified, doing further damage to enemy machinery (if cutting by itself isn't enough)

Edit

Maybe there's some outdated law that forbids projection of a potentially lethal missile - updating the law to stop melee weapons has become tied up in the bureaucracy.

Answer 16

Many many good reasons in many answers here, but here's another one: your projectile weaponry is too dangerous to yourself to use at close range.

Why would depend on the weapons. Missiles are not something you want exploding into your face - if they can damage an enemy mech they can presumably damage yours as well. If you're using energy weapons, maybe it's not the weapon itself but the splashback as it burns its way into the enemy's armour, sending a jet of incredibly hot plasma right back at you.

So when you get close enough for this to be a risk, you switch to something that doesn't set you on fire.

Answer 17

The author of Dune, Frank Herbert was brilliant in that, although he did not use mechs, in his novel the weapons cannot almost never be used, they have laser weapons but they don't use them because if a laser weapon hits something protected by a shield that result in an atomic explosion.

In a world where weapons are so advanced and damaging that they can cause devastating side effects it is preferable to not use weapons:

Conquering a city: if you are fighting for a city maybe you want to avoid civilian kills and damaging useful buildings and facilities. Bullets cannot pierce armored stuff they just get deflected and hit random targets, you could use U-238 bullets but those are radioactive and not suitable for urban environments, RPGs are not an option again because they can do big damage to small sections (yes they can pierce armors, even reactive armors, but if the target is big and moving they do less damage).

Killing specific targets: If you want to kill only a specific target maybe you can prefer melee weapons because you save money on ammunition.

You want actually to kill pilots: If mechs are heavily armored it is likely that just hitting a obstacle could kill the pilot but leave the mech undamaged (you now head bones are weak, and mechs armor is very hard). Using melee weapons could result in killing pilots and leave mechs undamaged so you ca reuse them (if you are able to win the battle).

You actually own the "ignitor": there was a novel where a scientist find the weapon that could put a end to all wars, it was a weapon able to ignite anything flammable at any distance, so basically that weapon was able to destroy all ammunition and explosives and fuels, this open for worlds with chemical weapons, battery powered mechs, melee weapons and biological warfare. So that weapon in reality just not ended all wars, but removed explosives.

If you have not explosives, melee weapons are most efficient: yes you can use a laser, but lasers require great power and have the side effect of make blind everyone in nearby surrounds not wearing protective sunglasses (and anyway cutting through a whole mech armor is not an option, to cut metal with laser you need to move it slowly, no target would stay still).

Probably you want weapons to put enemy mech unable to move, and then later use eventually a laser to cut it while he is hold still on ground.

Answer 18

Energy Shields

You know those things that stop particles from going through your ships when they travel with their faster-than light speed? Well slap one on the mech - the faster the enemy projectile the more resistance the shield exerts. King of like falling in water with high speed vs slowly dipping in.

Sure you can chug a grenade under the shield and blow the mech's legs, but if the shield is very tightly wrapped around the body instead of an umbrella style that tactic doesn't work anymore.

If you want to still keep ranged weapons viable then you can just make the shield generators "overheat" if they sustain too much fire. Tanks (and maybe soldiers) will be equipped with the same shielding and remain relevant (although at a disadvantage).

The return of mele weapons

So now using a "slowly" swinging sword isn't that unfeasible anymore... Your mechs can run around and chop tanks, infantry and other mechs as much as they like without worrying about being turned into cheddar cheese.

Make them carry a metal shield (or a fancy energy one with same shape) and sword for extra protection and epicenes while fighting. Though if melee is truly the best options then you'd probably see most mechs use Shield & Spear instead

... just don't step on a landmine

Answer 19

"I mean, shoot the legs and they can't move much anymore."

There's your answer. Mechs need to be armoured to withstand enemy action and remain in the fight. But they can't be too heavily armoured because then they won't be mobile enough, which defeats much of the purpose of a mech.

Given that the greatest threat to a mech would be ranged projectile weapons, often aimed at the legs, this means that the logical armour selection would be reactive and/or composite, similar to what is used on armoured fighting vehicles today. The end result is that in close-quarters combat against another mech, their projectile weapons are likely to be ineffective against one another (assuming they can even track at that range).

Now I don't know much about the effectiveness of reactive/composite armour against mech-sized melee weapons, and unsurprisingly there appears to be little research on this topic. What I do know is that a melee weapon of that size is going to have a lot of mass, which means a lot of kinetic energy; quite possibly more than a projectile-defeating layer of armour can absorb. (Not to mention the difference between how that energy is being applied; compare a blade's edge strike against a sabot round impact.)

Thus a melee weapon has two purposes for a mech. Firstly it's likely to be the only viable way for mechs to engage each other at close quarters. Secondly it makes use of one of the innate strengths of a mech - massive amounts of power, backed by high mass (both of the weapon and the mech itself).

Answer 20

Pathos

If creator of the universe practices Rule of Cool, then inhabitants of the universe would eventually notice this and deliberately do cooler things. Cool things would work despite boring physics and common sense.

Well, from their perspective, Rule of Cool would be a part of physics itself.

Take a look at spiral power as an example.

Answer 21

Projectile weapons may become prohibited

Similar to chemical weapons, projectiles could be prohibited in war. They often go off target, result in significant non-target casualties, and are a very blunt instrument for war.

It's possible that such weapons may simply be banned in the future, leaving melee combat as the only option.

Answer 22

There's some great answers in this thread already, but I'll add a couple reason in-universe reasons from various mecha media.

Mobile Suit Gundam

In the original UC Gundam universe, the development of compact fusion reactors led to the discovery of the Minovsky particle. This particle is high-energy and had a side-effect of forming a regular grid-like lattice when released into the air or space. This lattice has many in-universe uses, but the most important aspect of it was that it acted as a sort of particle-based Faraday cage, blocking electromagnetic radiation, including radio waves. With Minovsky fusion reactors being used in most starship, and soon miniaturized by the Federation of Zeon and used in their new Mobile Suits, Minovsky interference caused radio-guided and other non-Line of Site weapons to become effectively useless, moving combat back into close quarters. Mobile Suit combat became the standard after the One Week Battle, and most Zeon mobile suits were armed with standard solid ammunition weapons like machine guns and rocket launchers, so many of the were equipped with Heat Axes and other physical close combat weapons as well.

Most of the other Gundam franchise shows don't really follow this, however, so it only really makes sense in the UC universe.

In Gundam Iron Blood Orphans, all Gundams' armors are made of beam deflecting materials (to encounter the Mobile Armor they were designed to fight against) and a Mobile Suits' frame is almost indestructible, so the only way to take down a Mobile Suit is to use blunt force to deform the frame (skeleton, if you will) enough to squeeze the pilot to death.

BattleTech/Mechwarrior

When the BattleMech was first developed during the days of the Terran Hegemony and up until the last days of the Star League, Mechs were a combination of mobile tank and artillery platform. However, after the collapse of the Star League and the beginning of the Succession Wars plunging the galaxy into total war, the method and means to design and manufacture advanced weapons, and indeed even some Mechs, was soon lost or no longer understood. Warfare devolved into close combat affairs, with Mechs becoming heirloom objects passed down through the generations. Most combat also took place in urban areas, where close-combat weapons like the Hatchetman Mech's eponymous hatchet has the advantage, while many Mechs also make use of fists or feet to deliver blows of tons of steel.

For almost 300 years, combat in the Inner Sphere is waged like this, until the return of the Clans. As a contrast to the Inner Sphere, the Clans are descendants of a commander named Alexander Kerensky who fled the Inner Sphere before the First Succession War and established a new culture of peoples. With advanced weaponry and brilliant military tactics, they took the Inner Sphere by surprise and cut a deep swath toward their main objective: Terra. However, the Clans are also an honor-bound military culture, and they look down on things like close-combat as dishonorable. This, along with some clever maneuvering by another faction in the Inner Sphere, ComStar, allowed the Inner Sphere to defeat the clans at Tukayyid and halted the Clan invasion.

Answer 23

Mecha can probably be defined to range from anything the size of powered exoskeletons (which are currently being researched/developed by DARPA) up to the Godzilla-sized monstrosities of the Gundam series and other works of fiction.

In a space-station or similarly enclosed environment the need for well-armored peace-keeping soldiers may necessitate some use of these smaller-sized mecha, while the close-quarters environment and high-cost and high-risk of collateral damage may pose strong disincentives to the use of projectile weapons. (All police would carry batons/tasers/swords instead of guns if a hull-breach is an immediate and apparent danger, right?)

If these peace-keeper models are mass-produced to far greater extent than their full-scale total war counterparts, then it seems quite feasible that a number of different locales may see a large number of these smaller bots used in conflict even if the big-dollar top-tier bots are more effective in combat. Furthermore, if the littler bots are in widespread use they might already be on-the-scene as conflicts develop, meaning they might transition from peace-keeping to warlike roles to fill the void as heavy mecha are still in transit.

Answer 24

Have you ever played with 'gak'? It's a non-newtonian fluid made from corn starch and water. If you hit it or apply a lot of pressure, it hardens, but if you press it slowly, your hand will slip in.

I've always thought that in these melee-ed mech futures, it must be that shield technology works a similar way. Something going too fast? Apply resistance. Something moving slow? Probably just the pilot getting in or out, let through. A melee weapon isn't fast-moving enough to trigger the shield resistance, so it it is suitable for taking out enemy shielded vehicles and mechs.

Answer 25

The environment might require it

It has been suggested that the lack of line of sight in an urban environment, especially coupled with dense fighting where ammunition might be limited could advantage a fast, repeatable weapons system. This also seems to allow things like laser cannons. These sorts of atmospheres would also help explain the odd absence of air superiority already mentioned.

Dense atmosphere

But what if the 'air' of the world the fight was taking place on was especially opaque? A near equivalent on earth would be fighting in a very strong sandstorm, or underwater. This sort of environment could plausibly prevent optical weapons and small arms fire from functioning, and an urban or choppy terrain would prevent/discourage rocket based weaponry.

Reactive atmosphere

A highly flammable or chemically reactive atmosphere, perhaps one very high in gaseous hydrogen and oxygen, would cause large fires/explosions when a rocket or laser was fired. The mechs could well be shielded or armored sufficiently to prevent machine gun fire from being strong enough to damage them meaningfully for the weight it imposes on the holder.

There might not be room on a mech to defend against everything

It's not hard for me to imagine that the shielding/defense/armor strategies that defend against lasers/swords/rockets might all be different. If there wasn't a unified technology to defend against the varied attacks you would have to make speed/size and energy tradeoffs in defending a mech. These things are going to be awfully heavy, and on the sort of rough terrain already described as preventing tanks, maybe you just can't have all the different technologies on the mech and still have it able to transverse the terrain. It could also provide to much of a power or resource drain on either the mech or the society building them. This sort of scenario is, to some extent, why we don't only use tanks as it is. There are just places you can't go if you weigh 100 or 200 tons.

Those weapons don't exist

As in some of S.M. Stirling's books, you might imagine a world where the technology for lasers/rockets either can't or doesn't exist. If gunpowder and rocket fuel were much more complicated to invent, it doesn't necessarily preclude the invention of computers, robotics and nuclear power. So you could have this sort of weaponry evolve from a society that never develops any sort of firearm. A similar scenario could be accomplished by envisioning the development by an alien species with very limited sight. They might never develop firearms because they can't use them, but they are able to develop mechs that interface well with their other senses, and are armed as the society has always been, with swords and the like.

Answer 26

Stealth/Ammo

For me the first step to figuring out why I'd prefer melee over ranged weaponry was thinking about what other situation I would prefer melee in. My first thought was zombies. In every book about zombies it is recommended that you bring melee weapons only. Why? Because they're quite and wont attract more zombies and because you don't have to worry about running out of ammo.

This same logic can be applied in military combat. In stealth mission you may want to get in, kill a target, and get out without anyone knowing. Sure a sniper could do this but I'm sure you can think of some reason that long range silenced weapons are out of the question (i.e. shielded walls, underground bunker, etc.) So instead of going in guns a'blazin you can sneak in (the best you can with a mech) and do you job without alerting the whole infantry down the street.

During this stealth mission you may find yourself way behind enemy lines. With no time for a supply drop or perhaps your command doesn't even formally recognize that you're there, you're on your own. Why risk running out of ammo and becoming sitting ducks, your sword never runs out of killing power.

Answer 27

Hmm... assuming a world where humanoid mecha are a viable combat option, it would depend on the weapon, really.

Normal melee weapons, as already said, can be used until they break, instead of needing to be reloaded every so often; even a mecha-sized bladed weapon will be heavy enough to make a good club if the blade dulls; this prevents the mecha from becoming a giant, helpless bullseye after it runs out of ammo. Assuming the mecha already has humanoid arms so it can cover a wider area with its ranged weapons, they're also more cost-effective than ranged weapons.

Melee energy weapons, on the other hand, would mainly differ in that they can be more efficient than ranged energy weapons. A lightsabre, for example, bleeds very little energy while active, except when in contact with another object. A ranged weapon, on the other hand, would consume energy every time it's fired, regardless of whether the shot hits anything or not. This could potentially allow it to remain operational longer, or get in more attacks before having to refuel, assuming it isn't offset by the energy consumed while closing in.

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Alterntively, it could be used to help counter mecha with ranged weapons. All things considered, most mecha-sized ranged weapons are going to be unwieldy at point-blank range, meaning that if you can get close enough for melee, you can destroy or heavily damage the mecha with little resistance. This could lead to the production of melee-oriented mecha for veteran pilots, which combine melee weapons and high maneuverability & speed to serve as "mage killers", closing in on ranged units while evading their attacks. This, in turn, would lead to ranged mecha being given backup melee weapons so they can defend themselves up close, and soon enough all mecha will be armed for both close- and long-range combat.

This is especially true if the mecha are designed for aerospace combat, and thus will be much more maneuverable than purely land-based units. There's a very real possibility that they'll be able to approach enemy units very quickly, which would mean that giving them melee weapons would be a logical choice.

Answer 28

1. More damage

Momentum: m1*v1 = m2*v2

Whatever damage a missile, cannon, or armor piercing round does, it can be dealt significantly higher in melee.

A 2-ton sword will deal far more damage than a 20kg AP missile.

2. Recoil

Past a certain point, firing heavy cannons will cause so much recoil that it will topple a mech. Missiles will require a lot of fuel to carry a heavy payload.

You'll still get recoil through melee, but a good pilot can control it in such a way to prevent from falling over.

3. Ripping off limbs

Missiles and rockets can have great armor piercing and damaging internal components. However, they are ineffective for simply ripping off another mech's arms.

A heavily armored head could be able to withstand high explosives and a direct plasma blast. But put two tons of force behind a punch and it can probably rip the head off, even if the mech's arm is broken in the process.

Answer 29

Why Mecha/Mechs at all?

I believe the plausibility lies with instinct. Is it easier to lift and stack cargo crates with a crane or lift and stack bricks by hand? The brick stacking does not require much in the way of training; you already know how to operate your hand and arm. Assuming the tech level is sufficient where the system is integrated with the user, and the system operated as a sort of augmented reality where the nerve impulses controlled the machine and provided sense feedback ("what am I grabbing, what am I stepping on" kind of stuff).

We will probably see them first in industrial and exploratory roles in inhospitable terrain. There are some pretty cool logging technologies being used right now like the Hexapod, it can walk where trucks and tracks can't go to harvest trees. Logging operations in mecha would probably be about like clearing brush for a human.

This only works where the mecha is an extension of the user and integrated into their nervous system. Just operating a mecha-shaped machine would likely make it more complicated.

Answer 30

Both sides possess a weapon that destabilizes explosives. It's an energy projector that can't be shielded against. (I forget the story but some major Sci-Fi author has a book (novella?) based around such a device, although used for peaceful purposes.) Get too close to such a generator and any warheads detonate, any rockets take off, any bullets fire. In such a battlefield you're not going to carry anything of the sort, thus you are limited to melee weapons, lasers, railguns and coilguns.

Lasers have severe power density problems. The sort of laser you could mount on a mech would be hard pressed to do much to enemy armor but would cause you severe heat problems. Both railguns and coilguns won't be able to do much given the short barrel length possible on a mech and if you manage to put enough punch into them you run into the recoil problem mentioned in another post.