Defense systems that shoot projectiles out of the sky have become one of the most important components of modern warfare, so much so that militaries face a diminishing supply. Since the start of the war in the Middle East, Iran has launched 23 cruise missiles, 498 ballistic missiles and a staggering 2,141 drones at the United Arab Emirates, according to the Emirati Ministry of Defense. Yet the glittering towers of cities like Abu Dhabi, Dubai and Sharjah stand largely unharmed, and fatalities have been minimal.

That is a testament to the effectiveness of modern military air-defense systems, which track and target missiles traveling faster than the speed of sound and shoot them out of the sky with another missile, saving many lives and sparing homes and property. The wars in Ukraine and now the Persian Gulf have highlighted the crucial role interceptors play in protecting cities like Kyiv or Tel Aviv or Riyadh, not to mention American bases in Bahrain, Kuwait and other Gulf states. But the supply chain behind those interceptors has been strained for years, stressed by the war in Ukraine, past engagements with Houthi rebels along the Red Sea and last year's 12-day war with Iran.

Missile defense experts are sounding increasingly dire warnings that if the war with Iran continues, stockpiles could become dangerously low, leaving allies around the world vulnerable to attacks. "We started this conflict with a big hole," said Tom Karako, the director of the Missile Defense Project at the Center for Strategic and International Studies in Washington. The center published a report on the depleting inventory of interceptors in December, before the current conflict even kicked off. "The hole got a lot bigger over the last month as we keep shooting these things off," Mr. Karako said of the interceptors.