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I'm trying to determine the added value of having literal light infantry in my story. This type of infantry is basically the same as the rest but weighs much less.

To truly determine the advantages and disadvantages of light infantry I want to eliminate what specific light materials and such would do for them, so I'm assuming that this infantry is exactly the same as a normal human but lighter. Its bones have the same strength, resilience, elasticity etc, it's fat has the same energy content, it's brain is just as capable, it's muscles just as strong etc. Nothing is different but one thing: Their weight. Currently, I'm exaggerating their weight difference in saying that the lightweight human is 10% of the weight of the "real" human.

Advantages as far as I can determine:

• higher jumps


• faster acceleration to their maximum speed


• slower terminal velocity


• can fall from higher before a fall will wound or kill


• better climbers


• can carry more weight before it becomes a problem -->techniqually not true. They can carry the same amount of weight, but the reduced amount of bodyweight means more weight of equipment can be carried.


• requires much less equipment to hover or fly.

Disadvantages as far as I can determine:

• slower falls --> when jumping or trying to run, it takes longer to reach the ground again, meaning you can run slower and take longer to recover from a jump.


• When in a car crash (or explosion) you are more likely to die --> your organs are easier to accelerate/decelerate causing them to receive more damage. This might be a moot point as there's also less force behind your own organs, IE they require less force to be stopped and thus might experience fewer problems from a crash.


• Similar to a car crash, being in a fight will mean getting hit is more lethal to you (might be just as moot a point).


• In hand-to-hand combat, you are much more ineffective as any blunt-force attempt has much less weight and therefore energy behind it (any other technique still works assuming you don't need your weight). Can be countered by wearing more heavy gear to compensate.


• high winds have much more effect on the light human


• much more problems handling recoil.

Lightweight humans (whose sole difference is weight, with strength and resilience unaffected) are basically a straight upgrade from normal humans. That improved strength ratio (muscle capacity vs body weight) means they can move faster and carry more stuff.

Your question identifies positives and negatives pretty well, but I would make a few corrections

• Fall speed is largely unaffected. Recall Galileo's experiments that objects fall at the same rate regardless of weight. Fall speed only changes significantly when the object is so light that aerodynamic forces [ie. air resistance] are similar to the gravitational force acting on an object. A lightweight human doesn't meet that criterion unless they are wearing a wingsuit or are EXTREMELY low density, like a balloon or aerogel.




• I think hits will be LESS lethal, as their bodies are easily accelerated away with an impact, rather than their bones/organs being forced to elastically resist an incoming blow while the body's momentum changes to match the blow. Imagine trying to pop an airborne balloon with a hammer.

Other thoughts:

• There will be a range of inconveniences for the lightweight humans interacting with objects designed for heavy humans. Heavy doors would have to be braced against to open them (hell, they might even lack the friction against the ground needed to open a big door), a backpack full of stuff would overbalance them (totally changed gait for carrying objects perhaps?), Heavy weapon martial art forms would be unusable as the centre of rotation for a human holding the weapon is vastly different.... Basically, I'm saying the lightweights will move and interact with the world in unusual ways, they are kind of like humans permanently living on the moon.




• We might expect the lightweight humans to end up weaker than normal humans, just because they don't experience the continual weight training of lugging a fat body around. Training may be necessary.




• I would expect lightweight humans to develop solo spear-based combat styles, taking advantage of their superior speed to evade and make lightning, piercing strikes to the opponent from range.

Light humans would also probably float better (if they are the same size than a normal human, they are less "dense") and could be able to swim with more burden than a normal man.

I think a lighter human would work very well in amphibious operations (crossing rivers, landing on beaches...): being able to swim carrying a heavier equipment, they could easily establish well-equipped bridgeheads.
Similarly, they would behave well also in difficult and soft terrains (mud, ice, high mountain in general, crossing rivers on improvised bridges), since they would stick less and the terrain would be less likely to collapse under their weight

One huge advantage is much easier logistics. Lighter people will burn less energy while doing anything than heavier people will. So they will need less food and maybe less water. They'll also be easier for vehicles to transport, especially in the case of aircraft. A big consideration for transport aircraft is load balancing. Lighter people will make that less of a problem. And for fighter or strike aircraft, every kilogram of dead weight you can save is one more kilogram of ordnance or fuel you can carry, or one less kilogram slowing you down. This kind of thing holds true even for pre-modern societies. Lighter people are easier for horses to carry, and they also are easier to pull in a chariot.

Word play aside, Your light infantry is probably not going to be a really good infantry at all. They could be useful at so many other things.

What you are proposing is that the light humans are the roughly the same size and shape of normal humans, just without the mass. To get to your proposed mass, you need some seriously radical changes to the basic materials in human anatomy. Think about it, your skelton alone is 15% of your overall mass. That by itself is half again more than your proposed light people. A bit can be done with air sacs in the bones, like birds, but probably not enough. So magic magic or radical science would be necessary to get a similar strength from an alternative material. Next you have muscle and other tissue That's a lot of volume to fill if you want to cover a normal sized human skeleton. Last but not least you have blood. it's made of water (sort of) and masses in a similar way. 5.5 liters of water masses 5.5 kg. So you end up in a place where the only way possible to get a 10% of the mass human is to use Magic or Extreme science fiction. But this only gives you a base of things you have to account for.

Now what can you do with them. Regular infantry is right out unless you have them carrying some sort of energy weapon with no recoil. That puts you in the sci fi category. In the era of muscle powered weaponry they simply will not have the mass to be effective. To strike hard with muscle power, you need momentum. Momentum needs mass, and these guys just don't have any. One standard human with a mace would wade right through a bunch of these guys in a world with normal physics. In a modern military, you need a variety of projectile weapons. These weapons have a lot of mass. When it comes to recoil, you do not get a pass on the laws of physics.

ONe thing you might consider for these ultra lightweight humans might be light Calvary. A role that means you have to move a lot of people and stuff really fast. Ranged weapons on a moving platform, whether that be horse or helicopter. Less mass means you can either move faster or carry more stuff. A light horseman can go farther, faster than the same horse with a standard human. Same goes for a helicopter or other conveyance. an 8kg pilot means you can carry 72 more kg of ammo.

Also, you could even look at all sorts of flight or glider possibilities for recon and intelligence gathering.