The United States military, as well as other militaries around the world, are racing to develop high-energy weapons—lasers, high-powered microwaves, and electromagnetic rail guns—in order to compete with near-peer competitors on the next generation of military technologies. But the electricity to power these systems will need to derive from somewhere, and so military planners are eyeing a new generation of energy-dense nuclear reactors, despite potential policy and legal challenges to doing so.

The Pentagon’s high-energy weapons efforts include the Navy’s planned deployment of a 60-kilowatt (kW) laser on a destroyer; the Army’s plans to field-test a 50-kW vehicle-mounted laser next year and an anti-cruise-missile 250- to 300-kW fixed system by 2024; and the Air Force test last May that shot down incoming anti-air missiles with lasers. The Navy and the Army are both working on electromagnetic rail guns, while the Missile Defense Agency is eyeing megawatt-class lasers for ballistic missile defense. Efforts abroad include Russia’s mysterious Peresvet laser weapon, deployed last year; and China’s efforts to build ground- and ship-based lasers. Both countries are also believed to be building ground-based anti-satellite lasers. China, which tested a railgun at sea in 2018, may be the first nation to deploy an operational version of that technology.

How will these energy weapons get their power? Commercial innovation in batteries, capacitors, and related storage technologies have expanded the options. But militaries are increasingly reexamining nuclear energy, whose power density and ability to operate for long periods without resupply make it attractive. Russia is building nuclear-powered ice-breakers, some of which may be combatant ships armed with 200-kW lasers. China is building a floating nuclear power plant to power its militarized, artificial islands in the South China Sea. In the U.S., the Navy is building the nuclear-powered Ford-class aircraft carriers to produce 25 percent more power than their predecessors, to feed new sensors, electromagnetic catapults, and high-energy weapons. The Army is considering mobile nuclear power plants, in part to drive high-energy weapons, an idea one retired three-star hailed as a potential logistics revolution. And should the U.S. build space-based lasers for missile defense, nuclear energy may be the only way to provide the needed megawatts.

All this raises key policy concerns in relation to international law, rules of engagement, and the laws of warfare. Basing, or even deploying, nuclear reactors in the territorial waters or land of an overseas ally requires the permission of the host government, which may be averse to expanding nuclear power as in the case of major bases like Yokosuka, Japan. Diego Garcia, an island in the Indian Ocean, provides another challenging case as the ongoing territorial dispute between the United Kingdom and Mauritius threatens the U.S. base there, and a nuclear plant would only complicate the existing dispute. The U.S. Navy already faces constraints on where their nuclear-powered ships can visit. Floating nuclear power plants, like those developed by Russia and China, face similar concerns if they transit foreign waters or, in the case of the South China Sea, are stationed in disputed territories. Similarly, mobile reactors, like those considered by the U.S. Army, would likely be transported by air, requiring permission of all overflight countries.

Beyond basing, a critical question is whether the U.S. military would own and operate these new reactors, as the Navy currently does, or whether they would pursue commercial alternatives, as the Army is considering. The U.S. Army report on mobile reactors noted that, with either government or commercial ownership, there are concerns about international rules and licensing that present potential barriers to deployment. In some cases, potential host countries do not even have nuclear regulatory agencies. Further, commercial ownership raises liability concerns, both in the case of a military incident or an accident. International nuclear liability treaties are not well harmonized between the U.S. and most of its allies, especially when it comes to the unique concerns of transportable reactors.

Using nuclear power for high-energy weapons also creates targeting dilemmas for the U.S. and foreign militaries. High-energy weapons and their support infrastructure, including reactors, may be initial targets in a conflict. The social, environmental, and reputational impacts of damaging a nuclear reactor, particularly on a country’s home territory, or with effects on a third country, could lead to conflict escalation and international condemnation. While customary international humanitarian law may assign special protection to “nuclear electrical generating stations,” there is some debate over the scope of that rule. Nevertheless, as with any military objective, the traditional condition of proportionality applies, and reactors can still present collateral damage concerns when they are located near civilians, in international waters, third-party host states, or outer space.

Nuclear-powered laser satellites could aggravate concerns about nuclear arms controls as such systems could be used for anti-ballistic missile or anti-satellite applications. While the Outer Space Treaty prohibits weapons of mass destruction in orbit, it does not prohibit other types of weaponry. During the Cold War, Soviet military space reactors raised calls for bans on space nuclear power, particularly after one accidentally crashed in Canada. Recent calls for space arms control have been unsuccessful. As with terrestrial nuclear-powered lasers, the unique role of laser satellites would make them early targets in any major power conflict, leading to risks of collateral damage from radioactive and dangerous space debris, as occurred after the accidental 2009 collision involving a decommissioned Soviet nuclear satellite.

It appears likely that these futuristic weapons systems will be deployed. The U.S. military has been at the forefront of energy innovations for decades, and these new developments offer opportunities to continue that leadership. However, their complex policy consequences must be thoroughly evaluated first.

Image: An electromagnetic railgun is fired at 10.64 megajoules with a muzzle velocity of 2,520 meters per second at Naval Surface Warfare Center, Dahlgren, Va., Jan. 31, 2008. Photo: U.S. Department of Defense