Last month the US Air Force accidentally released a document soliciting proposals for upgrades to its Ground-Based Strategic Deterrent (GBSD), an intercontinental ballistic missile (ICBM) now under development and slated to replace the current nuclear-armed ICBM fleet. This document indicated interest in a hypersonic glider modification to the GBSD, prompting speculation that the United States might be planning a nuclear-armed hypersonic missile.
This would be a dramatic reversal of US policy, which currently limits hypersonic weapons to conventionally-armed, non-nuclear roles. A spokesman for the Department of Defense was quick to point out this policy, asserting that the solicitation did not signal plans for deployment.
Still, the lines between hypersonic missiles and nuclear-armed ICBMs have long been blurred. Many of the hypersonic weapons now under development could, once deployed, carry nuclear warheads as easily as they could conventional explosives. Regardless of current policy, these weapons will influence global nuclear security for decades to come.
Hypersonic missiles, ICBMs, and dual-use capabilities
The policy distinction between conventionally-armed hypersonic missiles and nuclear-armed ICBMs is central to the US contention that hypersonic weapons should be excluded from nuclear arms control agreements. Abandoning it could lead adversaries to mistake the launch of a conventionally-armed hypersonic missile for a nuclear attack, increasing the likelihood of unintentional nuclear war.
Yet, despite its importance, this distinction is one of policy, not technology. Mounting a hypersonic glider onto an ICBM rocket is not a new idea. In flight testing, the United States launches hypersonic gliders on Minotaur IV rockets, modifications of old Peacekeeper ICBMs that were previously armed with nuclear warheads.
The Air Force has long considered deploying hypersonic weapons on these modified ICBM rockets. Given that a Peacekeeper ICBM carrying ten small nuclear warheads had a range of ~6000 km, one could easily accelerate a hypersonic glider to speeds sufficient for intercontinental range flight (defined as greater than 5500 km). It is therefore unsurprising that the Air Force might envision pairing the GBSD, their newest ICBM, with a hypersonic glider.
Even if these hypersonic weapons were designed for use with conventional, non-nuclear explosive payloads, substitution with a nuclear warhead is unlikely to be a problem. In recent US flight testing, hypersonic gliders have carried up to 450 kg of extra tungsten metal as ballast, heavier than many modern US nuclear warheads. Russia’s hypersonic glider, the Avangard, is specifically designed to carry nuclear payloads.
Just what are hypersonic weapons for?
Regardless of whether the Air Force pursues a hypersonic modification to its nuclear-armed GBSD, the advent of hypersonic weaponry is a pressing nuclear security concern. The GBSD is slated for deployment in 2027. Meanwhile, US hypersonic weapons currently under development—which will likely be capable of carrying nuclear warheads over long ranges, should the United States choose to do so—might be fielded as early as 2023.
While it would not represent a new technical capability for hypersonic weapons, the recent commotion about a potential hypersonic GBSD draws attention to the uncertainty that accompanies the US hypersonic weapon program. The Department of Defense has yet to make clear precisely what role these weapons are meant to play in US strategy.
Until a clear rationale for these weapons is articulated, statements regarding US hypersonic weapon policy should be taken with a grain of salt. That policy could change quickly if hypersonic weapons begin to look attractive for nuclear use. Given their intrinsic dual-use character (conventional or nuclear), the world would be a safer place if these weapons were swiftly integrated into the global nuclear arms control regime, before they are widely deployed.
Featured image: An unarmed Minuteman III intercontinental ballistic missile launches during an operational test at Vandenberg Air Force Base, Calif. U.S. Air Force photo/Senior Airman Ian Dudley