When General Mark Milley outlined the U.S. Army’s future priorities in 2017, he said that new long-range missiles, improved tanks, and better-armed, better-trained infantrymen were vital to America’s domination of the next major conflict. But those plans, the then–Army chief and soon-to-be chairman of the Joint Chiefs said, came with an important caveat: The upgrades would be useless unless the military came up with a more effective air defense. “None of the above,” he noted, “will matter if you are dead.”The Trump administration is finding out just how much air defense matters in its war with Iran. The open-ended campaign poses the biggest-ever test of America’s 21st-century sky shield, a network of weapons to protect against incoming missiles, drones, and ordnance.So far, that system has mostly held up against the barrage of drones and missiles that Iran has fired at U.S., Arab, and Israeli targets since Saturday morning. But that won’t remain true indefinitely. U.S. military leaders may soon be forced to choose between protecting troops and civilians near Iran and maintaining U.S. combat readiness against larger, more consistent threats from Russia and China. Even though President Trump and other officials have suggested that the war could last at least four or five weeks, and maybe longer, the conflict in some ways has already become a race to weaken Iran’s missile-launch capacity before Tehran can deplete Washington’s finite air-defense supplies.Trump appears aware of the threat. In a late-night post on Truth Social yesterday, he said that the U.S. munitions stockpiles “have, at the medium and upper medium grade, never been higher or better” but added, “At the highest end, we have a good supply, but are not where we want to be.” He went on to blame Joe Biden for not replacing weapons provided to Ukraine.Tom Karako, who heads the missile-defense project at the Center for Strategic and International Studies, told us that the strain on U.S. weapons stockpiles could become so severe that the Trump administration would be forced to dispatch troops to Iran—a move that Trump has not ruled out—to neutralize underground missile-launch sites and hunt down Soviet-designed Scud missiles. “We can’t afford to keep doing this,” Karako said. “That’s why there’s such an urgency to finish the job.”Before Trump launched Operation Epic Fury on Saturday, Chairman of the Joint Chiefs of Staff General Dan Caine and other officials had expressed concerns about the supply of interceptor missiles and about the threat to troops of not having enough, U.S. officials told us. Even with plentiful supplies, U.S. air-defense systems are not impregnable. Six American service members have been killed since the war began, all of them in an Iranian retaliatory strike on a U.S. facility in Kuwait. Iranian attacks also killed civilians in Israel and the United Arab Emirates, hit a British base in Cyprus, grounded much of the region’s airline travel, and brought maritime commerce to a near halt in some of the world’s busiest shipping lanes. The State Department closed embassies in Kuwait and Saudi Arabia after a drone attack on the U.S. diplomatic compound in Riyadh and urged hundreds of thousands of American citizens to depart 14 Middle Eastern nations.Read: [Trump opens the Pandora’s box of assassination]The buildup for Iran has already come at a strategic cost: The military added to Middle Eastern stockpiles ahead of Epic Fury by pulling supplies from Asia and the Western Hemisphere, the two areas the administration has identified as its national-security priorities. Last summer, the Trump administration cited a limited supply of interceptors as a reason to temporarily suspend a shipment of weapons, including missiles that run on the Patriot defense system, to Ukraine.“We were told some months ago that they were worried about what we could supply to Ukraine because it would deplete our magazine capacity,” Senator Angus King of Maine told us. “That implies that there is a limit to what we have.”At the outset of the war, Iran was estimated to have roughly 2,000 medium-range ballistic missiles capable of hitting Israel, and 6,000 to 8,000 short-range ballistic missiles capable of striking the Gulf, former U.S. and Israeli officials told us. The bottleneck for Tehran, however, is missile launchers, Daniel Shapiro, a former Pentagon official and former ambassador to Israel who is now a fellow at the Atlantic Council, told us. Medium-range missile launchers, which Israeli and U.S. forces are now racing to destroy, are believed to number in the mid-hundreds, Shapiro said. But the United States and Israel have far fewer interceptor missiles available to shoot down those Iranian projectiles. That means that U.S. success may hinge on being prudent about when it fires those interceptors. Experts say that Iran will have little trouble replenishing its massive supply of drones, which can be made relatively quickly and cheaply while still causing serious damage. (U.S. Central Command declined to comment on the matter.)A formidable ballistic arsenal has for decades been Iran’s most potent offensive weapon, considering that its air force has been neutralized by past conflicts and years of sanctions. Now those missiles are the central pillar of Iran’s defense against the U.S.-led attacks on its leadership, its conventional weapons, and its nuclear facilities. Every time Iran launches a missile toward a U.S. base or ally in the region, the U.S., Israel, and Gulf states must fire costly interceptors. The rate of attrition is all the greater because air defenders typically fire two interceptor missiles at an incoming projectile to ensure its destruction.Read: [The death of Khamenei and the end of an era]The U.S. military hasn’t provided a precise figure on Iranian ballistic-missile launches since the conflict began. Qatar said today that it has been the target of more than 100 in the past four days; the UAE said today that it has intercepted more than 170 ballistic missiles since Saturday. Iran has at times launched a cluster of missiles and drones simultaneously at the same target. Some experts calculate that the United States and Israel have, between them, enough supplies to blunt Iranian attacks at their current pace for several weeks; longer than that would be more difficult, though Trump sought in his Truth Social post to downplay the risk. “Wars can be fought ‘forever,’ and very successfully, using just these supplies,” he wrote.Mick Mulroy, a former Pentagon official and Marine Corps and CIA officer, told us that the conflict may come down to a battle of logistics and supplies. “Broadly, this is really about attriting Iran’s ability to wage war,” he said.The U.S. uses interceptor missiles to knock down enemy missiles before they can reach their target, which experts liken to hitting a bullet with a bullet. Defensive platforms now in the Middle East include the THAAD system, which can intercept ballistic missiles; Patriot batteries that can shoot down ballistic and cruise missiles (in addition to U.S. Patriots, some Arab partners have their own); and sea-launched standard missiles. The military also has shorter-range defense systems to deploy outside an embassy or base, such as the C-RAM and the drone-targeting Coyote. The Pentagon uses electronic warfare systems to jam or disrupt drones, and military pilots can shoot down cruise missiles and drones before they land.So far, Operation Epic Fury has aimed its fire in large part at Iran’s ballistic-missile capabilities, a tactic designed to eradicate the threat at its source. In more than 1,700 strikes, the U.S. has targeted launch sites, command-and-control centers, missile warehouses, and roads used to transport both missiles and launchers. In previous conflicts with the United States and Israel in 2024 and 2025, Tehran fired massive retaliatory barrages, including dozens of missiles in each salvo. This time, Iran has fired smaller clusters of missiles in an apparent attempt to preserve firepower and maintain a steady rhythm of strikes over a longer period, Danny Citrinowicz, a former senior Israeli military intelligence official, told us. Israel is now battling on another front, too, after missile strikes from the Iranian proxy Hezbollah, in Lebanon. If other Iran-linked militias jump into the fight, strains on U.S. supplies will be even more severe. The war with Iran, however long it lasts, will require the United States and its allies to replenish their stockpiles. The production of interceptors has been plodding. The U.S. made an average of 270 advanced Patriot missiles a year from 2015 to 2024, according to the Center for Strategic and International Studies; the number of THAAD missiles produced was even lower. In a high-tempo fight, those interceptors can be used astonishingly fast. The Pentagon is now prioritizing air defense as it seeks to accelerate weapons manufacturing and revitalize the United States’ sclerotic military-industrial base, recently unveiling a deal for Lockheed Martin to more than triple its production of Patriot missiles over the next seven years. But no contract has been signed, and, if congressional budgetary fights persist, it’s unclear whether those missiles will be delivered on schedule.Kelly Grieco, a fellow at the Stimson Center, a think tank, told us that because of the U.S.’s military dominance and annual budget of roughly $1 trillion, Americans don’t often have to consider the need for strategic sacrifices. But there is likely to be a dearth of air defense supplies. “This is one of the few places where the defense trade-offs are really acute and really visible,” she said. Even if those supplies outlast Iran’s ability to retaliate, the Pentagon may have to ration what it can spare for other theaters, whether that’s the demands of Ukraine as it seeks to repel Russian forces after four years of war or the western Pacific, where U.S. forces are in a constant state of alert should China decide the time is ripe to move on Taiwan.