Earlier this week I attended a very thoughtful and stimulating debate on the modernization of U.S. nuclear missiles hosted by the Project on Nuclear Issues (PONI) at CSIS. The debate addressed the merits and downsides of two planned U.S. nuclear delivery system recapitalization efforts: the Ground Based Strategic Deterrent intended to replace the Minuteman III ballistic missile system, and the Long-Range Stand-Off (LRSO) cruise missile that is supposed to replace the AGM-86 air-launched cruise missile (ALCM). The ALCM is a dual-capable missile, meaning it can carry either a nuclear or conventional payload. While the LRSO is planned to be only used for nuclear missions, in a conflict scenario it would be hard to discern between it and a conventionally-armed cruise missile until the moment of impact.

One topic raised during the debate was the effect of the LRSO on strategic stability, an important and hotly debated issue. The advocates of the LRSO downplayed the destabilizing potential of the system by pointing out that the United States has used dual-capable cruise missiles in past conflicts. Concerns about strategic stability should be kept in mind, they argued, but the United States has a track record of using dual-capable cruise missiles while safely navigating such concerns.

This argument may be technically true, but it ignores a critical fact: all past uses of dual-capable cruise missiles were in conflicts with countries that did not have nuclear weapons—not between two nuclear-armed countries. Policymakers should be wary of arguments that use historical evidence to dismiss or downplay the negative effects of LRSO on strategic stability because there are no adequate past cases to test such arguments against.

Such an oversight is especially damning when one considers the likely targets of the LRSO. The missile, and the B‑21 bombers supposed to carry them into combat, are designed to penetrate the dense and increasingly complex air defense networks of “near-peer” adversaries like China and Russia. This enhances the ability of the U.S. Air Force to hold high-value targets, such as command and control facilities, military bases, and enemy nuclear forces, at risk. However, the same bombers could also be armed with conventional cruise missiles.

The ambiguity about whether a cruise missile is nuclear or conventional poses a dilemma for nuclear-armed opponents in a conflict or crisis situation. If the United States starts destroying high-value targets necessary for the effective use of nuclear weapons, will adversaries feel pressure to either escalate the conflict in the hope of getting the strikes to stop or use nuclear weapons while they still have some ability to do so? Will the adversary be able to quickly determine what kind of cruise missile was used against it if communications links are damaged and they suspect more missiles are incoming? The decision to develop and field the LRSO greatly affects these questions. If the United States only possessed conventional cruise missiles, then the target would be more confident that they were not under nuclear attack.

Countries that the United States has already used dual-capable cruise missiles against did not possess nuclear weapons. Therefore, the United States and the targeted countries did not have to grapple with the dilemma. Firing Tomahawk missiles at a Syrian air base or using ALCMs to punish Saddam Hussein for attacking a Kurdish safe haven does not carry the same escalation risks as using conventional cruise missiles to tear down Russian or Chinese air defense networks.

It is misleading and irresponsible to point to past uses of dual-capable cruise missiles to downplay concerns about the LRSO. Historical evidence cannot settle this debate because there are no cases of the United States using a dual-capable cruise missile against a nuclear-armed adversary. There should be a lively discussion of the LRSO’s impact on strategic stability, but that discussion needs to have sound arguments.