New Study Warns U.S. Suffering Extreme Depletion of Missile Stockpiles Due to Iran War

Defence affairs - Def-Geopolitics

The U.S. Armed Forces depleted their stockpiles of critical missiles to dangerous levels during the country’s seven week war against Iran, resulting in a “near term risk” that could leave it vulnerable, according to a new assessment published by the Center for Strategic and International Studies (CSIS).

Intense combat operations have exhausted a staggering proportion of the country’s most advanced weaponry, including Precision Strike Missiles (PrSM), Patriot, THAAD, SM-3, and SM-6 air defence interceptors, and Tomahawk cruise missiles, with figures remaining classified by the Pentagon. Although the Pentagon maintains it has sufficient firepower to continue operations against Iran and its strategic partners, the CSIS report warns that the depletion of munitions has fundamentally undercut the United Sates’ ability to fight a major war, which has particularly serious implications for the Pacific theatre, where the United States faces peer and near peer challenges from China and North Korea respectively. 

Analysts at CSIS have warned that rebuilding U.S. arsenals will be a slow and costly process, with an expert from the think tank cited by CNN observing that it would take “one to four years to replenish these inventories and several years after that to expand them to where they need to be.” Statements by Pentagon officials have consistently been assessed to be downplaying the extent of the fallout from the war. Iran’s sustained air defence capability limited the ability of hostile aircraft to operate deep inside its territory. This prevented U.S. and Israeli aircraft from relying primarily on low cost gravity bombs to strike targets, and meant that high cost missiles launched from the air, from on land, and from at sea were more heavily depended on to strike targets from safer distances. Lower value aircraft such as MQ-9 Reapers, which were widely used to operate deep inside Iran, have suffered very high rates of losses to local air defences. 

Analysts have estimated that the U.S. launched attacks on more than 6,000 Iranian targets in the first 10 days of attacks, almost all using costly beyond visual range weaponry, while also firing at estimated more than 2000 anti-ballistic missiles to intercept Iranian counter strikes. By the final week of March, the Navy was estimated to have expended close to 1,000 of Tomahawk cruise missiles, of a total arsenal of between 3,000 and 4,500 in its total inventory. To place this in perspective, just 57 Tomahawks were included in the United States’ defence budget in 2025, despite depletion of the arsenal from strikes on targets in Iran and Yemen in 2024-2025. Alongside anti-ballistic missiles from the THAAD, system, one of the most heavily depleted inventories has been that of GBU-57 bunker buster bombs, which estimated to have been almost totally used up, while being extremely challenging and costly to replace with costs of over $370 million per bomb.

Director of the Missile Defense Program at CSIS Tom Karako has been among several to warn that while the Pentagon claims its stockpiles are sufficient for current operations, the continued high-rate expenditure has placed immense pressure on the U.S. Armed Forces’ long-range weapons inventory. He highlighted that the United States' failure to maintain sufficient missile stockpiles over the past few years has now forced massive depletion in the war, putting military planning officials at risk of running out of ammunition. Karako further noted that avoiding ammunition shortages requires swift action from Congress and the Pentagon to replenish the ammunition replenishment budget, while particularly warning that shortages could seriously undermine warfighting capabilities in the Pacific.