When Eugene Stoner first introduced his aluminum and plastic Armalite rifle that would later become the basis for the M16 and M4, he scarcely could have imagined his little black rifle would still be in the hands of infantrymen more than 50 years later. Yet, after dozens of conflicts, Stoner's lightweight automatic rifle persists — though it's been modernized along the way.
The M16 evolved into the M16A1 all the way through M16A4 before being retired to non-frontline units. But along the way a shorter, handier carbine version was introduced. The earliest version of the M4 that featured most of the telltale aspects of the design was the CAR-15 SMG. Despite being labeled a submachine gun, the CAR-15 SMG still used the 5.56mm cartridge.
The SMG featured an overly-complex (yet functional) collapsible stock, shortened barrel and fixed carry handle. The biggest difference between early versions of the M16 and modern variations is modularity. Older models needed either modification, or special components to attach accessories like tac lights, lasers or optics. Yet underneath the anodized aluminum shell of every M4, lies the original M16.
Why does this matter? Because it shows that the M4 (in one form or another) is here to stay. It may evolve and grow, but the rifle itself will likely only leave U.S. service when something truly revolutionary emerges. Not a different rifle, nor a different caliber, but a different method of launching projectiles than smokeless powder altogether.
Imagine the cost and logistical nightmare of replacing all M4 rifles in service with all branches of the military. The price would be staggering. And that's largely why the Army balked at replacing the M4 several years ago — too expensive, and not enough of a "leap" in technology to justify the cost.
The only way Congress would green light a true replacement weapon system is if something arrived that instantly made all modern firearms obsolete.
What would that weapon be? It's difficult to pinpoint exactly what that might look like, but it's reasonably simple to determine what it wouldn't do – launch solid projectiles.
First on the chopping block – solid or liquid-fueled rockets. Sounds obvious, but inventor Robert Mainhardt successfully built a series guns that fired small rockets known as microjets back in the late 1950s. While the rifles (really launchers) had many issues, the core problem that could never be solved is the lack of velocity close to the muzzle.
Whereas gunpowder-propelled bullets are at their peak velocity at the muzzle of the barrel, rockets accelerate much more slowly. So at close range the rounds would be ineffective. Add to this the complex nature of the round's construction and the limited magazine capacity due to projectile size, and any weapon utilizing these rounds is objectively inferior to the M4.
What about magnets? The concept of a railgun isn't new and has been around since the World War I, and the German air force even designed anti-aircraft batteries of railguns in WWII – but these never even reached prototype status. The biggest issue has been power supply, the large magnets required to launch projectiles at hypersonic speeds consume insane amounts of energy.
One of two electromagnetic railgun prototypes on display aboard joint high speed vessel USS Millinocket (JHSV 3) in port at Naval Base San Diego. The railguns are being displayed in San Diego as part of the Electromagnetic Launch Symposium, which brought together representatives from the U.S. and allied navies, industry and academia to discuss directed energy technologies. (U.S. Navy photo by Mass Communication Specialist 2nd Class Kristopher Kirsop/Released)
Modern physicists and engineers have successfully developed methods of magnetic propulsion that don't require as much power, and have made railguns feasible. So feasible that railguns are currently being developed by the US Navy with one slated to deploy on a vessel this year.
For the uninitiated, the advantage of these guns over traditional cannons or guided missiles has to do with the incredible velocities of the projectiles themselves. When the Army worked alongside the University of Texas at Austin's Center for Electromagnetics, they found that railguns could fire a 4-pound tungsten rod at nearly two miles per second, or 6,840 mph. At this velocity, the round not only defeats the armor of a main battle tank like the M1 Abrams, it passes clean through both sides.
Sounds great, but currently the technology isn't capable of being scaled down for use by individual soldiers. Also, the amount of power required still isn't man-portable with current battery technology. Though even if it were, railguns are currently single-shot weapons, making them inferior to the M4 in close combat or urban fighting.
So what is the likely replacement for the M4? As crazy as it sounds, a directed energy weapon. Think more Star Trek than Star Wars – weaponized lasers would offer an enormous advantages over solid projectile firearms and cannons.
One of the largest benefits of a laser weapon would be velocity. With your beam traveling at the speed of sound and being relatively unaffected by gravity. So hitting a distant target wouldn't require adjusting for wind or drop. But that's impossible, right?
The Afloat Forward Staging Base (Interim) USS Ponce (ASB(I) 15) conducts an operational demonstration of the Office of Naval Research (ONR)-sponsored Laser Weapon System (LaWS) while deployed to the Arabian Gulf. (U.S. Navy photo by John F. Williams/Released)
Actually, the United States and Israel have been developing and deploying a Tactical High Energy Laser for more than a decade. Israel's IDF even used the THEL to shoot down 28 incoming Katyusha rockets in 2000. Like the railgun, the THEL is currently far too massive and consumes too much power to be man-portable. But, the same thing was said about computers only a few decades ago. Who knows, maybe the M5A2 laser carbine is only a decade away.
Until then, the US military is stuck with upgrading, tweaking and tuning the M4 carbine. It might not be bleeding edge tech, but the old warhorse still accurately slings lead further than most soldiers can see, and it doesn't weigh a ton.