Every weapon has its nemesis. The invention of the tank led to anti-tank guns; the rise of aircraft led to anti-aircraft guns; and now the growing use of military unmanned aircraft is spurring the development of multiple types of countermeasures, including lasers, guns and jammers.

Lasers are the most exotic of anti-unmanned aerial vehicle weapons, and the U.S. has several directed energy weapons projects underway. The Army's Space and Missile Defense/Army Strategic Forces Technical Center in Huntsville, Alabama, the lead Army agency for developing high-energy laser weapons, is working on three systems with anti-UAV capabilities.

The High Energy Mobile Laser Test Truck, or HELMTT, aims to demonstrate a vehicle-mounted 10-kilowatt laser rugged and practical enough to use on the battlefield. The project was originally the High Energy Laser Mobile Demonstrator (HEL MD), until the Army opted to mount a smaller laser on a Heavy Expanded Mobility Tactical Truck. HEL MD managed to shoot down a 22 to 55 pound Class 2 UAV during a 2014 test at the High Energy Laser Systems Test Facility at White Sands Missile Range, New Mexico. The Army's Space and Missile Defense Command plans to eventually develop a 100-kilowatt weapon.

Boeing's Company Laser Weapon System (Boeing)
Boeing's Company Laser Weapon System (Boeing)

While HELMTT focuses on mobility, the Solid State Laser Testbed (SSLT) aims at maximizing lethality. The SSLT is a demonstration project at the High Energy Laser Systems Test Facility, where directed energy weapons are tested against rockets, mortar shells and UAVs to determine their effectiveness against various aim points and materials.

"If you want to kill a UAV, you have to know where to shoot," said Richard DeFatta, director of the Air and Missile Defense Directorate at Space and Missile Defense Command. "Just shooting a hole in the wing may not bring it down. You have to know which component to aim at."

The Robust Electric Laser Initiative (RELI) focuses on designing a more efficient high-power laser for HELMTT. The project will conclude in late 2016 when Lockheed Martin is scheduled to deliver a 50-kilowatt laser. Meanwhile, the Air Force is using RELI technology, as is the Navy for its Ground-Based Air Defense laser development program. In fact, the Navy's 30-kilowatt Laser Weapon System, installed on the destroyer Ponce, destroyed a ScanEagle UAV in 2014.

The Compact Laser Weapon System damaged a moving, tethered UAV during testing in West Virginia. (Boeing)
The Compact Laser Weapon System damaged a moving, tethered UAV during testing in West Virginia. (Boeing)

As for private initiatives, Boeing has unveiled a mobile laser, based on off-the-shelf manufacturing lasers, that can be used against UAVs. The Compact Laser Weapon System (CLWS), a Boeing internal research project, is a 2-kilowatt weapon that shot down a Class 1 UAV with a 10-second laser shot during the Pentagon's Black Dart anti-drone exercise in 2015.

A Boeing data sheet puts the range of CLWS, in a counter-UAV role, at less than 3 kilometers, which extends to less than 7 kilometers when employed to blind ISR sensors.

The 600-pound CLWS can be man-packed into four cases, mounted on a tripod, or eventually be mounted on vehicles and helicopters.

Lasers certainly aren't the only way to kill drones. The Army's Research, Development and Engineering Center has used a 50mm cannon to shoot down a UAV last year as part of its Extended Area and Protection Survivability program.

But lasers are the most high-tech drone-killer, and what is interesting about these laser weapons is how far they have come since the bad old days of bulky, expensive and dangerous devices. No one wants to go back to chemically powered lasers that gulped tons of toxic fuel, like the Airborne Laser, a 747 airliner-mounted ballistic-missile killer that was canceled in 2011. Instead, the military is concentrating on electrically powered lasers.

"With an electric laser, you just run it off a battery or generator," DeFatta said. "The only consumable is fuel, which is cheap. The amount of fuel you use for a laser shot is typically less than $30."

In fact, the lasers themselves aren't the focus anymore, but rather how to make lasers mobile and useful on the battlefield.

"I will cautiously say that the laser issue has become more engineering than physics," DeFatta said. "Yes, the laser is important and we still have development to do. But the engineering around the vehicle is the more important piece of this. And making it reliable and useable."

Boeing's CLWS uses a commercial industrial laser, the kind found in places like automobile manufacturing plants, rather than some expensive, custom device. The trick for Boeing was to make that laser mobile, rugged and able to hit its target.

"We found some COTS [commercial-off-the-shelf] lasers that provide good power and beam quality, and we're combining those with our capability in acquisition, tracking and pointing, and beam control," said David DeYoung, director of Boeing Laser & Electro-Optical Systems.

"The takeaway is that it's good enough," DeYoung adds. "You can keep spending money on more and more powerful lasers, but why not use what's good enough?"

What is also interesting is none of these projects are specifically designed to shoot down unmanned systems. They are designed for a variety of targets, perhaps most importantly missiles, rockets and mortar shells. They can also be used to blind ISR sensors or disable improvised explosive devices. Thus, UAVs are only one potential target, and not the most difficult.

"Actually, a UAV to our laser system is a much easier target," DeFatta said. "They flow slow, low, and they're easy to track. With a mortar shell, you almost have to have automatic engagement because of the timeline. Most UAVs are also fairly soft. There are a lot of ways to kill them, everything from blasting a hole in it to cutting a wire. The payloads are pretty soft to a laser, too."

Experts are cagey about the precise details of a drone-killing laser, such as the diameter (though they are said to be the size of a dime or a quarter). The same applies to the number of seconds that the laser needs to focus on the target, or "dwell time." Boeing claims that CLWS knocked down a Class I UAV weighing less than 20 pounds in 10 seconds.

Dwell time is a function of how much energy can be applied to the target. "The more power you get, the less dwell time on a target to have the same effect, if the range is equal," DeFatta said. "So at a given range, you can get twice as much laser energy, and dwell half as much. It's a little more complicated than that, but the rule of thumb is 'twice the power, half the dwell time.' "

But even when the laser dwells long enough to have an effect, there remains a dilemma between destroying the unmanned aircraft or merely disabling its sensors. "We would like, in most cases, to shoot it down," DeFatta said. "That makes the soldiers happy, as opposed to telling them: 'We killed the sensor on that thing, even though it's still out there flying around the racetrack [flying its surveillance pattern].' "

It's important to remember that there are drones, and then there are drones. The Army and Boeing are aiming at Class 1 and 2 UAVs, which are small battlefield drones typically flying at less than 3,500 feet and at a speed of 100 miles per hour or less. These lasers can take down an unmanned aircraft like a four-pound Raven, but not a one-ton Predator nor an airliner-sized Global Hawk.

But then, why should they? Conventional air defense weapons — guns, surface-to-air missiles, jet interceptors — can handle the larger unmanned systems. It's simply cheaper to use a laser to down the small fry. "We're primarily talking small UAVs, things we don't have other countermeasures for," DeFatta said. "We can already kill the smaller UAVs, but do you want to send a Stinger missile to kill something like that?"