Whether or not it’s prudent for the United States to continue its war with Iran, a new constraint is becoming public knowledge: the depletion of crucial U.S. munitions. According to the Center for Strategic and International Studies (CSIS), the United States has used up as much as half of certain key defensive and offensive missiles in this year’s conflict with Iran. The running down of these munitions diminishes the White House’s ability to project power and emboldens its adversaries.

On the latest episode of FP Live, I spoke with Tom Karako, the director of CSIS’s Missile Defense Project, to understand the extent to which the United States has expended its inventory of missiles, and what that means for its foreign policy. Watch the full discussion on the video box atop this page, or try the FP Live podcast on Apple, Spotify, or YouTube. What follows here is an excerpted transcript of our discussion.

Whether or not it’s prudent for the United States to continue its war with Iran, a new constraint is becoming public knowledge: the depletion of crucial U.S. munitions. According to the Center for Strategic and International Studies (CSIS), the United States has used up as much as half of certain key defensive and offensive missiles in this year’s conflict with Iran. The running down of these munitions diminishes the White House’s ability to project power and emboldens its adversaries.

On the latest episode of FP Live, I spoke with Tom Karako, the director of CSIS’s Missile Defense Project, to understand the extent to which the United States has expended its inventory of missiles, and what that means for its foreign policy. Watch the full discussion on the video box atop this page, or try the FP Live podcast on Apple, Spotify, or YouTube. What follows here is an excerpted transcript of our discussion.

Ravi Agrawal: So we’re going to discuss several different types of munitions. Some of this is going to get wonky, but I just want to start with the one that seems to be the most well-known: the Patriot missile interceptors. Just very briefly, can you explain how they work in layman’s terms and why they seem to be so popular?

Tom Karako: They’re popular because people want to be defended against missiles, and missiles have become weapons of choice globally. In fact, there are 18 nations that count themselves members of the “Patriot family” and operate one or another kind of Patriot missile. So you’re alluding to essentially two different kinds: Patriot Advanced Capability-2 (PAC-2) and -3 (PAC-3). PAC-2 is a “blast frag”; it explodes. PAC-3 is “hit to kill”; it collides with the target. All of that is possible because sophisticated radars detect a threat, track the threat, develop a fire-control solution, and tell the missile where to fire. It’s a very sophisticated system, and that’s why the demand for it is out the door and around the block.

RA: And what is your understanding of how many of these the United States had before the war, which began in February, and how many it has now?

TK: The Pentagon—correctly—does not release exact numbers of inventory necessarily, or the numbers that have been used. That’s for good reason. Having said that, according to some public statements in the budget requests, you can guess there were probably about 2,500 or so before the war. Some of my colleagues have estimated on the basis of open-source information that probably over half of that, perhaps as many as 1,200 or more, have been expended. Those are probably for the United States; there’s also a number of Patriot operators in the Middle East—Saudi Arabia, United Arab Emirates, and others—that, according to news reports, have also been expending a lot of their........

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