US military planners face critical shortages of defensive munitions that could constrain any offensive against Iran, according to defense officials and analysts. During last year's 12-day conflict, the US and Israel burned through interceptor stockpiles at an unprecedented rate, raising concerns about magazine depth for Terminal High-Altitude Area Defense (THAAD) systems.

Washington has ordered fewer than 650 THAAD munitions since 2010, yet fired up to 150 during the 2024 conflict alone. The Pentagon's limited production capacity extends beyond THAAD systems. The navy expended roughly 200 SM-2 and SM-6 missiles against Houthi militants in the Red Sea, while planning to purchase only 12 SM-3 missiles this fiscal year for $445 million.

These shortages force difficult strategic calculations. Military officials warn that a sustained air campaign against Iran would require conserving defensive munitions for other theaters, potentially leaving Israel to shoulder more of its own protection. The munitions production issue stems from inconsistent Pentagon demand signals, which have discouraged defense companies from boosting output. With interceptor stockpiles already strained by conflicts in Ukraine, the Middle East, and against Houthi rebels, US military leaders acknowledge that any air campaign would be fundamentally governed by available magazine depth.