From finding the biggest stick, to nuclear arms race, humans have a natural tendency to attempt to outgun their opponents, either to defeat them or to provoke enough fear to establish order, or just to discourage others from doing the same to them. On this basis it can be assumed that humans will develop new weapons from new technologies or even to develop new technologies to make new weapons possible.
Weapons that fire a solid projectile via electromagnetism have been hypothesized and if this technology were to come to fruition then these rail-guns or coil-guns may very well replace current firearms. These weapons, other than being more expensive than current small arms, would probably fire a similar projectile to similar effect, except that it may be possible to very quickly change a power setting and an adjustable rail to switch the rail-gun from one calibre to another within minutes. Essentially it could be used as something akin to a P90 for fighting in built up areas against an unarmoured opponent while reducing the risk of collateral damage (a higher powered projectile may pass through a hostage-taker into a hostage), and then switched to something more like an M82 for an urban sniper role. This could happen if current trends continue to work towards modular platforms for small arms rather than a single object (consider the XM312 being converted to an XM307 within minutes, and the XM8 family)
A laser weapon would work by heating it's target with a concentrated beam of light (not necessarily visible) causing it to melt or burn. If a sufficient and portable power supply where available, these weapons could become cost-effective and logical.
As anti-tank weapons they can most easily damage optical, electro-optical and thermal sensors.
As an air defense weapon they could hit any target they could see (at the same wavelength) within their effective range unlike guided missiles or ballistic projectiles which have to compensate for the movement of the target, so long as the light was not refracted somehow.
- Many counter measures against laser damage to missiles have been proposed, these range from ablative coatings on the missile to spinning the missile to spread the heat over a larger area.
Many ideas and concepts about plasma canons, plasma gun or just plasma weapons has been done in both real life, and in science fiction literature. The idea is to take the ionied plasma gas, and turn it into another stage: liquid. And then use it as a burning material, but as a firing laser. Both concepts about plasma weapons that fires laser-look-a-like beams has been made, but also ideas about weapons that fires heated liquid plasma.
Unmanned Aerial Vehicles (UAVs)
Currently important in reconnaissance, UAVs will become increasingly important in warfare against slow moving targets. This will put a premium on light weapons that they can carry easily. Initial 'weapons' are likely to be designed to damage sensors. UAVs will be able to approach very close to their targets, and target sensors with great accuracy. Currently limited by communications links to the ground control stations, the sensitivity of sensor technologies and the reluctance of commanders to provide total autonomy for weapons releases.
Unmanned Ground Vehicles (UGVs)
In the early stages of development, UGVs primarily role looks to be either reconnaissance in dangerous areas (with the high value control station/soldier located in a safe location) or recovery of high value assets/injured soldiers from dangerous locations. Current development is centered upon sensor technology and data processing of sensor data. It is important to differentiate UGVs that have the ability to perform and complete a pre-determined "mission" without human assistance, from remote controlled platforms such as bomb disposal equipment that provides humans with extended sensors, and need constant human supervision. UGVs with attached missile weapons platforms have been trialled, but the released weapon destroyed the platform when launched. As with UAVs, there is a reluctance of Commander's to provide total autonomy because of the risk of friendly fire incidents. Some of the most advanced research is happening in the automotive industry, but this is associated with car following and keeping safe distances from other vehicles and other obstacles along roadways. There is still significant work to be done before robust systems are available to traverse off road conditions safely both to the vehicle itself and to the environment and by-standers.
- See nanoshield discussion at LifeBoat
Active Defenses / Active Protection
Active protection is a protection that seeks to prevent hits after the munition has already been launched at the target.
Active defensive suites can interfere with the guidance of guided munitions (decoys, jammers, concealment and possibly signature changes that break a lock). That's being called "soft kill".
"hard kill" active defensive suites seek to destroy/damage/deflect/turn incoming munitions and can also protect against unguided munitions.
Defensive combat against munitions (instead of only against the weapon-launching platforms) has been common in naval warfare since WW2 (anti-guided torpedo decoys, later air defenses and ECM against aerial missiles). It has also been practiced by air forces (radar jammers, chaff/flares decoys).
This principle (to counter munitions instead of only platforms) has been adopted by modern land forces since about the 80's (on a very small scale) and is becoming very popular.
It is quite predictable that active defensive suites (including hard kill) for armoured vehicles will become very relevant in the near future. There are about 50 such systems known.
The future of C-RAM (counter rocket artillery mortar) defenses as a function of battlefield air defenses is less clear.
The widespread introduction of active defenses will add to the protection of modern land forces and likely influence the military technology offense-defense spiral very much.