The problem with firing additional interceptors is that there will be only forty-four to go around, and a commander would not necessarily know how many missiles an adversary is capable of firing. They might be launched all at once, in an attempt to swamp the defenses, or staggered in an effort to cause an overcommitment of interceptors early on.

Even if you have more optimistic assumptions about the interceptor’s success rate—say, 70 percent of missiles hit, or 80 percent—the mathematical conundrum remains: how many missiles can you safely expend from a limited supply to ensure the safety of millions of lives?

This terrifying exercise in probability underscores why the GMD system has been of limited comfort to nuclear strategists.

Unfortunately, the GMD system has also elicited repeated complaints from Moscow and Beijing—even though it does not constitute an effective defense against their nuclear arsenals. Their chief concern is likely that the missile defense system could cause U.S. leaders to grow overconfident, and thus more aggressive. If an American leader mistakenly thinks the GMD missile defenses are better than they really are, that could lead to escalating tensions and an ill-judged tendency to discount the threat posed by an opposing country’s nuclear weapons.

The GMD defense system, even with its flaws, represents a remarkable technical achievement—a feat widely described as “striking a bullet with a bullet.” However, its current track record of frequent testing failures highlights that it remains far from the desired level of reliability, even as a defense against a limited nuclear strike. It’s vital that American leaders recognize that the GMD system comprises at best an uncertain hedge against the danger posed by a weaker foe, rather than a dependable shield from nuclear attack.

Sébastien Roblin holds a master’s degree in conflict resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing and refugee resettlement in France and the United States. He currently writes on security and military history for War Is Boring.

Image: KN-15 on parade, 2017. Wikimedia Commons/Creative Commons/@LionFlyer