About what topic did Congressmen Doug Lamborn of Colorado and Jim Langevin of Rhode Island ask Defense Secretary Jim Mattis during his first week on the job? “Lasers,” of course, for they run the Congressional Directed Energy Caucus. That’s a thing, apparently, for as one of us wrote in November 2013, “lasers will save us all—if they ever work.” Directed energy has been a fetching technological idea for decades, but as Sandra Irwin wrote in National Defense in July 2015, the technology seemingly “has perennially been on the cusp of a major breakthrough.” Last summer, though, Jason Ellis of the Lawrence Livermore National Laboratory wrote a report for the Center for a New American Security (CNAS) about a coming “inflection point” in development. “Technically credible, operationally usable, and policy friendly directed energy weapons” could soon be available—if only the Congress would fund them, and the Pentagon would prioritize their adoption. So, if the congressmen get through to the secretary, what could be possible?

Lasers weapons have been overhyped and underwhelmed ever since the first beam lit up. For decades, most efforts at high-energy laser weapons, such as the US Navy’s Mid-Infrared Advanced Chemical Laser (MIRACL) and the US Air Force’s Airborne Laser (ABL), have been chemical lasers. These have not proven practical as weapons. To begin, deploying them means adding volatile chemicals to the logistics train. The cost of a shot is more akin to that of expensive cannon ammunition—though that’s still much cheaper than guided missiles. The systems are quite large, involving multiple full-size trailers to hold to the chemical storage tanks and associated equipment. The chemical reactions that produce the beams are intense. Northrop Grumman notes that the exhaust from its Skyguard chemical laser is non-toxic, but the exhaust is similar to that of a jet engine, with a no-go zone of 30 meters.

The ABL made for a particularly famous but ultimately failed effort. That massive chemical laser was mounted on a 747 airliner, and intended to destroy ballistic missiles in boost-phase ascent. Cruising within range of a such a valuable target in an airliner was not an operationally relevant concept, so former Defense Secretary Robert Gates cancelled the program in December 2011. It’s thus notable that Lt. Gen. Ellen Pawlikowski, head of Air Force Materiel Command, cautions that we should “calibrate” our expectations of what lasers can accomplish. She once oversaw the ABL program.

Yet hope persists. As Yasmin Tadjdeh wrote for National Defense last August, the allure of lower cost is much of the interest. The marginal cost of melting a path through the engine block of an enemy’s truck may be a few dollars, for just a liter’s worth of fuel. Putting a Hellfire on that target expends about $100,000. The Israeli military rejected chemical lasers as a concept for its Iron Dome, but the missiles today cost at least $50,000. The defenders fire them at rockets costing less than $1,000. As I wrote in November 2012, the economics work only because the Gazans are destitute, and can’t afford enough outgoing rounds.

What may have changed in the past few years is the practicality of solid-state lasers. That design concept enables compact sizes that only require electricity to operate. The problem has been heat; at weapons-grade power levels, they generate enough to destroy the lasing medium. This is a result of their low efficiency and the mechanical difficulty in cooling a solid substrate. In a chemical laser, the flow of the chemicals themselves extracts the heat. Recently, however, American weapons engineers have demonstrated lasers that coherently combine the output of multiple fiber lasers at 30 kilowatts, and that is scalable to 100 kilowatts. Each individual fiber laser is able to stay below the thermal limit, while a single fiber laser at these levels would self-destruct. Perhaps more promising is DARPA and General Atomics' High Energy Liquid Laser Area Defense (HELLADS), in which coolant flows through the solid lasing medium to extract waste heat. HELLADS has already been demonstrated at 50 kilowatts, and the company thinks that it can produce a laser weapon for its Reaper drones at 50 to 300 kilowatts.

Apart from cost, the other enthusiasm is for the limitless magazine. Thus did the US Navy deploy last year a functional Laser Weapon System (LaWS)—the formally-named AN/SEQ-3—on the transport ship Ponce, currently stationed in the Persian Gulf. This 30-kilowatt bundle of welding lasers does not even produce a coherent beam, so the overlapping waveforms incur destructive interference in power-on-target at predictable ranges. Otherwise, though, the weapon is most adequate for short-range defense against drones and small boats. The Ponce could employ its Phalanx gun or an $800k Rolling Airframe Missile too, but either way, its ammunition load is constrained against an incoming small boat swarm. In the long run, the Navy would really like weapons of 150 kilowatts, for lighting up threats at longer ranges.

If those power levels at that size and weight prove operationally feasible, practical deployments of short-ranged weapons will proliferate—even to aircraft. Northrup Grumman’s AN/AAQ-24 has been protecting Army, Air Force, and special mission aircraft since 2005 with a laser dazzler designed to damage the optics of incoming heat-seekers and other electro-optically-guided missiles. They even market a podded version for legacy aircraft and commercial airliners. Others have followed suit, such as Israeli firm Elbit, which equipped the French presidential transport, as well as the airliners of El Al. But dazzlers are only a stopgap, as more sophisticated imaging IR seekers “may be very resistant to laser jamming,” and radar guided missiles are immune.

This explains the drive for lethal lasers that can destroy any type of incoming missile. The USAF has already hired Northrop Grumman to begin work on a prototype self-defense laser pod for fighter jets that could destroy air-to-air and surface-to-air missiles. General Carlton Everhart, head of Air Mobility Command, would like to get those on his transports and tankers to support operations in defended airspace. Apart from self-defense, Lt. Gen. Brad Webb, head of Air Force Special Operations Command, expects to test a laser on an AC-130 within a year with an eye toward offensive applications. Used offensively, a laser offers unique advantages over kinetic options, in particular the ability to scale effects and disable vehicles without destroying them while minimizing collateral damage. His predecessor, Lt. Gen. Bradley Heithold was so enthused that the notional weapon has been called the “Heithold laser”. Could an AC-130 armed with offensive and defensive lasers fight its way through air defenses?

Then there is space, the domain in which laser have captured the imagination of fiction writers. That’s understandable, because satellites are particularly vulnerable to laser attacks. Bill Gertz warned in the Asia Times just last week that the Chinese military has been working on directed energy for attacking space assets for over a decade. American efforts disappeared from public view with the cancellation of the Space-Based Laser Integrated Flight Experiment in 2002—long before the recent advances in solid-state lasers. Since then, either nothing has happened, or too much to talk about.

Our friend David Foster of Naval Air Systems Command cautions that all new awesomeness carries along its own vulnerabilities. Weapon systems wholly dependent on megawattage will go Winchester when the power goes down. Restoring partial power might not be enough, though at least the old-school guns may fire on a trickle from the diesel generators. Another limitation is the rate of fire. Like guns, lasers engage sequentially: charging the capacitors takes time, and the weapon must pivot towards and dwell on each ingressing target separately. Missile batteries offer greater range and some simultaneity: vertically-launched weapons can get airborne first, and vector towards bandits and vampires on cue from the ship. Lasers are also dependent on the quality of the air they pass through. Despite some success in fog, any type of particles in the air will disperse laser energy. With China already planning on filling the skies with smoke to block American lasers, pollution is now a defense.

Laser-based defenses also face growing competition from new kinetic options. The Navy’s Hyper Velocity Projectile not only aims to arm railguns, it promises to add a missile defense capability for existing gun barrels on land and sea. The Air Force Research Lab is pursuing a Miniature Self Defense Munition for aircraft defense, while Orbital’s Helicopter Active Protection System targets RPGs and MANPADs. And Boeing’s High Energy Laser Mobile Demonstrator will face competition from new mobile guns and missiles to defend ground forces against drones, rockets, and mortars.

However, probably the greatest indication of the reality of laser weapons is the growth of defenses against them. The Navy and Air Force are investigating coatings to reflect or redirect lasers and materials to dissipate heat to delay destruction. Ablative surfaces offer a double benefit in that the vaporization of the material dissipates thermal energy and produces a gas that absorbs directed energy. Ultimately, the best defense against lasers might just be more lasers. Adsys Controls’ Helios system tracks lasers to their source and uses a dazzler to disrupt their beam control. Even further down the road, the interaction of lasers and the atmosphere could turn from a weakness to a strength. BAE Systems’ Laser Developed Atmospheric Lens concept promises to use a laser to ionize a portion of the atmosphere and create a “deflector shield” against laser weapons.

CNAS’s Ellis thinks that more money is needed. Adjusted for inflation, the Defense Department’s spending on directed energy is down 84 percent from its peak at the end of the Cold War. That research, however, produced almost nothing useful, at least in the short run, explaining the terminal skepticism of policymakers. In his own report last year, Council member Byron Callan argued that forcing more money won’t force the technology to maturity. All the same, he called directed energy a “defense disruptor,” as it could upend the business of more than one defense contractor. Indeed, little known firm Kratos developed the LaWS in service aboard the Ponce. Nevertheless, government-spending research firm Govini calculates that the leading winners of laser weapons contracts so far have been traditional contractors Northrop Grumman, General Atomics, Lockheed Martin, Boeing, and Raytheon. The last may be particularly vulnerable to improvements in laser weapons, as missile sales account for more than a quarter of its revenues.

What’s less clear is how this technology would provide an enduring advantage for the United States. Similarly vulnerable to the disruptive change of directed energy is any military organization that depends on satellites and airpower for its supremacy. The advantages of cost and magazine depth combine to produce a real offset in laser weapons, but may also restore some ascendancy to the defensive. Don’t then count on those AC-130s or any other large manned aircraft to fly through air defenses, self-defense lasers or not. They are themselves big targets for bigger ground-based lasers, and the beam projectors can be hidden well away from the thermally obvious generators feeding them. With enough advance in laser technology, the US Navy may worry less about Chinese airpower in the western Pacific, but Chinese air defenders would worry less about US aircraft ingressing across the beach. Taiwan would be safer, but so would Beijing’s suzerainty on the mainland.

James Hasik is a senior fellow at the Brent Scowcroft Center on International Security.

Julian A. Platón is an international security researcher in Houston.