How long can the United States sustain the war against Iran?

WashingtonDonald Trump is relying on the military hegemony of the U.S. military to sustain a military campaign in Iran "for as long as necessary." The U.S. president said on Monday that the war could last. "four or five weeks", but that if necessary they still had "capacity for more time". This is not what the military leadership was saying two weeks ago, when General Dan Caine, Chairman of the Joint Chiefs of Staff, outlined to the president the list of risks involved in attacking Iran: one, the high probability of casualties—six American soldiers have already died; the other, the depleted Pentagon arsenal after defending Israel in the region and four years of supplying weapons to Ukraine. How long can the US afford to wage war against Tehran?

The US offensive employs Tomahawk missiles, ground-launched cruise missiles, and also the Patriot and THAAD air defense systems, with which they must cover all their positions in the region. The batteries of these two weapons can intercept both Iranian drones and ballistic missiles. Although the Department of Defense provided a list of the weapons used in the operation, called Epic Fury, it did not report the ammunition fired so far. The Pentagon did confirm that, for example, Tomahawk missiles were used in the first wave of bombing raids on Saturday morning to launch the attack on Iran. In the first 24 hours, "more than 1,000 targets" were bombed, as Caine explained on Monday morning. Firing a Tomahawk or activating the THAAD system takes only a few seconds, but manufacturing a single one requires at least a year. Replenishing them is not easy, and although the stockpile of the US arsenal is classified, it is clear that the United States' recent conflicts in the Middle East have consumed ammunition. The deployment of Tomahawks and Patriots to Ukraine has also depleted the stockpiles over the past four years. One of the Pentagon's major concerns is to quickly replenish this weaponry and maintain sufficient stockpiles for the other systems it has deployed in other regions. This is especially important because the Department of Defense operates on the principle of always having sufficient inventory and troops ready to deter or respond to any type of conflict with China.

Compromised situation of the THAADs

Of the seven THAAD systems that the United States has at its disposal, One is located in South Korea and the other in Guam. Both serve as a deterrent against North Korea and China, and this air defense system is precisely one of those most compromised in the last year. Needless to say, Beijing has been taking note of the rate at which Washington is consuming its arsenal, and is probably following the developments in the new war with Iran very closely.

During the 12-day war last June, the two THAAD systems in Israel fired continuously. It is estimated that of the 550 ballistic missiles launched by the ayatollahs against Israel, the United States neutralized many with more than 150 THAAD interceptors and approximately 80 SM-3 missiles, which can counter missiles fired above the atmosphere. The rate of fire was so intense that the Pentagon even considered bringing in other THAAD systems deployed in other sensitive locations in the region. The conflict concluded with 25% of the THAAD interceptor stockpile consumed. In other words, approximately a quarter of the entire ammunition inventory was depleted in just 12 days.

This situation raised concerns about a deficiency in the US supply chain. In 2024, the US produced only 11 new THAAD interceptor batteries, and only 12 more were expected during fiscal year 2025, according to the Department of Defense's 2026 budget estimates. The Center for Strategic and International Studies (CSIS) could already be warning of a shortage in the Pentagon's weapons stockpile. More recent CSIS analyses highlight the disparity between the volume of drones and attack missiles, produced at low cost, and the number of air defense systems, which are far more expensive to produce. A document published last December highlighted that the use and deployment of defense systems by the US has increased, while the demand observed in the industry that manufactures them "is inconsistent." In other words, weapons are being consumed faster than they are produced to replenish stockpiles. It also emphasized that "the deployment of THAAD systems during the summer of 2025 is concerning."

Even the United States acknowledges in its National Security Strategy published in 2025 The existence of a "huge gap" between low-cost offensive weapons and "the expensive systems needed for defense." "America requires a national mobilization to innovate powerful, low-cost defenses and produce the most capable and modern systems and munitions on a large scale," the text states, advocating for "reactivating the US defense industrial base."

Seth Jones, a defense analyst at CSIS, noted this weekend that "sooner or later, in some areas, such as defense systems, the US will begin to suffer from ammunition shortages." He added: "I believe that neither Israel nor the United States has enough munitions, offensive or defensive, for a war that goes from lasting weeks to lasting months."

THAAD ammunition is not the only type of ammunition that has been decreasing within the arsenal. During the Twelve-Day War, the US also deployed a classified number of Patriots in Qatar to defend its Al Udeid military base against Iran's response to the bombing of its nuclear facilities. Furthermore, the June operation came just after nearly a year of campaigning against the Houthis in the Red Sea. The operation, codenamed Rough Rider, also involved the deployment of Tomahawks, as well as some 200 SM-2 and SM-6 missile interceptors.