Western armies have been very interested in improving the individual equipment of soldiers since the end of the Cold War: Soldier modernization programs added body armour, better clothes, different camouflage, personal radios, lots of gadgets on the personal weapon and much more. The interest in driving quality up instead of quantity was apparently sparked in great part by the end of the Cold War.
These efforts are experiencing declining returns on additional improvements; most of the potential for equipment improvement that was accumulated during decades has been used up, and further improvements are difficult (unless you chose a stupid "universal" camouflage patter in between).
An old and extreme dream for soldier equipment is the superhuman strength and endurance exoskeleton. The existing prototypes are astonishing, but a rule of thumb says that moving parts are a source of trouble - and these exoskeletons are all about that. They might be too unreliable or require too much maintenance for decades to come.
Another strain of development is about the display of information; helmet visors, goggles or even contact lenses that display information without distracting the soldier from observing what he's meant to observe.
Nanotechnology and bionics are another field of interest. Super friction gloves that allow to climb a wall like a Gecko may become available, for example.
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There may be a change of direction in these "Soldier modernization programs"; they might actually switch from improving the gear towards improvement of the soldier himself. And yes, this may turn ugly.
DARPA today has a long-term, $3 billion program to help make such a “Metabolically Dominant Soldier.” In other words, the military is studying how to use technology and biology to meld man and machine and transcend the limits of the human body.
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Examples of possible improvements of a soldier's body functions:
Steroids are out; modern research is about blocking Myostatin, the protein that limits the body's muscle growth.
The effect of blocking Myostatin on health is apparently not very bad (or it's simply unknown) - maybe nature blocks it simply because super-strong beings are too hungry.
An "exercise pill" may trick the body into believing it has exercised. That would be a good addition to the Myostatin blocker because blocking Myostatin alone doesn't yield maximum effect without workout. The pill may help to increase endurance at the same time.
There's the prospect of drugs and other stuff that improves the speed of the human body. The brain's ability to coordinate movements and to react in time is a tough barrier to such improvements. Nevertheless, it's somewhat plausible year 2030 sci-fi that soldiers might almost run like top athletes while carrying their full equipment.
The combination of speed and strength may make aforementioned Gecko gloves pointless; one might become able to jump instead of climb over an obstacle.
Bones may break under the stress caused by great strength and speed. Someone might need to fix that problem as well.
It's an established medical procedure to use lasers to correct poor eyesight. A relatively new technology (wavefront aberrometry guided excimer laser operation) can boost the eyesight to 200% or normal eyesight. Maybe all well-funded armies will boost the eyesight of all (combat) troops (age 20-40 yrs) for free in the future.
Pills: Staying awake, concentrated and more
"Go pills". We've seen these for decades, and drugs may become even more important in the future as ever more performance is being expected by single "force multiplied" soldiers.
There's also research into super-memory pills and who knows - maybe there'll be a super-forget pill for after the war?
Another idea: A "less fear" pill.
I bet they'll forget to develop the ultimate pill for the soldier: One against boredom.
Drug: Survive huge loss of blood, shock
This is another possibility, and the drug may actually already be known.
Finally: Regenerate lost limbs
Some animals can regenerate lost body parts, such as tails. We can do that with our liver (if it wasn't lost completely). Many scientists are looking into this issue, and the civilian interest in such a therapy is large enough to mobilize much money. We might see results in a few years; relevant genes have already been identified.
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People, Ideas and Hardware in That Order! That's what Boyd disciples quote quite often. Well, the modernization efforts may indeed turn towards such an order in the near future. Let's hope that people learn how to make money off ideas, it would be a good idea to channel more incentives towards the creation of ideas as well.
Super soldiers with top athlete strength, speed, endurance, great survivability and super eyesight who don't even need to train much to get and retain their physical abilities are imaginable. Much money is being spent on project to achieve such advances.
Those soldiers would certainly be quite hungry, and well - I bet they'll forget to spend money on more tasty military meals.
Anyway; it's been interesting to do read reports about these possible advances and the idea is quite enticing. Such projects might face serious objections, though. Tuning a citizen's body functions is a violation of privacy that's difficult to exceed.
P.S.: My casual reading of the Nextbigfuture blog paid off. It was a great help in compiling this as can be seen at the links. Nextbigfuture is at times a bit questionable in its promotion of questionable science, but nevertheless an interesting read.
edit 2015: http://www.gizmag.com/biohackers-night-vision-eyedrops/36797/