Some Cautionary Notes on the New ‘Knife Missile’

On May 9, The Wall Street Journal revealed a secret U.S. missile that has been used in a handful of drone strikes in recent years. A variant of the Hellfire missile, the R9X carries no explosives. Instead, it relies on the sheer force of impact—it weighs 100 pounds and travels at a thousand miles an hour—plus a corona of six sword-like blades that fan out from its body in flight. The idea is that it can kill one single person without hurting those around them, thus reducing unnecessary harm. The reality is likely a little more complicated than that.

As it happens, this is not the first time that the Hellfire has been modified. A decade before the R9X was conceived, the Hellfire underwent the original transformation that gave us the weapon—feared by some, revered by others—that we all know today. Only that time, the goal was to make it more lethal and less precise. 

Here’s the backstory. Long before the age of drone warfare, the Army developed the Hellfire to help its helicopters kill Soviet tanks. In 2000, the Air Force used the missile to weaponize the previously unarmed Predator. The following year, the CIA began firing Hellfires from Predators at targets in Afghanistan. 

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But there was a problem. The original Hellfire used something called a shaped charge, which channels all the pressure generated by the explosive into a single extremely intense, but narrow, blast. This was good for puncturing thick steel armor, but bad, it turned out, for going after America’s new enemies. 

So in 2002, the CIA asked the Army’s engineers to make the Hellfire more effective against groups of people. The agency also wanted the missile to be able to kill everybody inside a room if the missile were shot through the roof or into the window. Evidently, the original Hellfire wasn’t quite up to that task. (This account is based on several interviews I conducted for a Wired story on the history of the Predator.)

The engineers’ solution was as simple as it was diabolical. They fitted the Hellfire with a sleeve of tantalum — a heavy metal — that burst upon detonation, forming a 360-degree barrage of shrapnel so hot, according to one source, that it could ignite diesel fuel. Now, a single drone strike could take out multiple people, indoors or outdoors. 

It took just two weeks for the engineers to complete the modification. That’s a millisecond in military acquisition time. But the effects of the project have been felt far and wide for years. One can only imagine how much carnage has since sprung from this single innovation—how many extra lives and limbs were lost (some justifiably so under the rules of war, others by mistake) thanks to nothing more than a simple sheet of machined metal. 

The R9X represents a conscious effort to step in the opposite direction. Perhaps the “flying Ginsu” Hellfire is a harbinger of a new chapter of strike operations that present little to no danger to innocent bystanders. Everyone can probably agree that this would be a welcome development.

However, there are a few notes of caution that we should keep in mind.

First, the actual employment of the R9X may end up being very limited, at least in the near-term. According to officials who spoke with the Journal, the missile has only been used about half a dozen times in recent years. 

This is likely because it serves its purpose only under very specific conditions: when a single person is targeted in an area where the probability of collateral damage from a regular Hellfire would be high. 

The fact that the missile has been employed so rarely also probably suggests that even under conditions where U.S. operators determined that there was some likelihood of civilian harm, regular Hellfires were used nonetheless. During the several years that the R9X has been available for drone strikes, dozens of civilians have been reported killed in regular Hellfire operations in Syria, Yemen, and Somalia. 

What we do not know is whether the R9X was available in any of those operations and, if it was, why commanders opted against using it. That is important information, with a direct bearing on the R9X’s real utility for reducing civilian harm. Without that information, it is hard to make a firm judgment on how much, if anything, the R9X will change.

Perhaps commanders with the R9X at their disposal held back for another reason. Because the missile is so incredibly precise, its effective use hinges on the availability of commensurately precise and accurate intelligence, which is exceedingly difficult to come by. Say, for instance, that one intends to kill a terrorist leader inside his home without harming his wife and children; one would need to know exactly where in the building he is located at the precise moment of the strike while also having knowledge that he is not, say, holding one of his children in his arms. (One also needs to be certain that the specific individual in the R9X’s crosshairs is, indeed, an active combatant—another matter altogether).

One official who spoke with the Journal suggested that the R9X could even be used to kill the passenger in a vehicle without killing the driver. This, also, would require specific intelligence, on who’s driving and who’s riding shotgun. 

Even if you did have such intel, the idea that you could fling a sword-twirling missile at nearly one and a half times the speed of sound at a moving vehicle with any certainty that it would only kill the intended occupant is, in reality, preposterous. It’s also hard to believe that one could put the missile into a room and not run a significant risk of harming multiple people beside the intended target. 

In other words, we should take care not to be over-sold on the technology's precision. After all, it’s still a missile. One official likened it to “a speeding anvil” falling from above.

Finally, there’s a possibility that the R9X could lead to more strikes, particularly outside of declared war zones, since it would expand the range of scenarios under which commanders could meet targeting policies that require a high level of confidence that no civilians will die. 

In practice, this means that whereas a unit equipped with only explosive Hellfires would be forbidden from making strikes in, say, a very crowded city thoroughfare, the same environment might be open season for a team with the R9X. (The Pentagon and CIA’s toolkit for covert strikes has been growing steadily over the years; in Somalia, it has also targeted al-Shabab with 500lb bombs and silent “glide bombs,” in addition to Hellfires and R9X’s.)

While any tool that might reduce civilian casualties ought to be celebrated and its use in place of less precise options encouraged, we should take care that it actually does what it claims to do, and that it won’t further bring down the threshold for lethal action—lest it become a double-edged sword akin to the six blades that fan out from the R9X’s skin, mere seconds before impact.