The Iran war has depleted key US missile stockpiles that could take years to replenish.
The same weapons used in Iran are also vital for defending Taiwan and supporting Ukraine.
Washington says it has enough munitions for now, but production is struggling to keep pace with demand.
The pause in US military operations against Iran has shifted attention from the battlefield to another question facing Washington: has the conflict exposed cracks in America's military arsenal? After nearly 40 days of intensive strikes and missile interceptions during Operation Epic Fury, the Trump administration insists the United States has more than enough weapons to meet its military objectives. But defence analysts say the pace at which advanced missiles have been used has highlighted a longer-term problem—many of those weapons take years to replace.
The debate reaches far beyond Iran. The same long-range strike missiles and air defence interceptors used during the conflict would be central to any future crisis involving Taiwan, continued military support for Ukraine or responding to threats from countries such as China, Russia and North Korea. The immediate question is not whether the US is running out of weapons today, but whether it can replenish its most sophisticated munitions quickly enough if another conflict erupts before production catches up.
The Iran war has exposed a production challenge
Earlier this month, US President Donald Trump stood alongside the heads of some of America's biggest defence companies at the Pennsylvania Defense and Innovation Summit with a straightforward message: build more weapons, and build them faster.
"We have the best quality in the world," Trump said at the US Army War College. "But we need a little more speed."
Standing beside Defence Secretary Pete Hegseth, Trump presented the initiative as an effort to strengthen American industry and reinforce what Hegseth called the country's "arsenal of freedom".
According to the BBC, those remarks came after a conflict that placed heavy demands on some of America's most advanced munitions. The US government estimates Operation Epic Fury has cost $37.5 billion (£28 billion), with the overwhelming share of that expenditure going towards munitions.
Before a ceasefire took effect on 8 April, the White House said US forces had struck more than 13,000 targets across Iran. During the same period, American air defence systems intercepted over 1,700 Iranian drones and ballistic missiles, showing that the campaign relied as heavily on defending against incoming attacks as it did on carrying out offensive strikes.
The New York Times has reported that Trump was advised against expanding military operations because doing so would further reduce US reserves. Trump has dismissed those suggestions.
"We have far more munitions than anyone in the world, and far more than we need," he told the Wall Street Journal.
The administration's messaging has also evolved. While Hegseth initially rejected suggestions that supplies were thinning out, he later told the Senate Appropriations Committee that the Pentagon needed another $87 billion (£68 billion) to address "critical shortfalls", including military equipment.
Exact figures remain classified, but estimates compiled by the Washington-based Centre for Strategic and International Studies (CSIS), cited by the BBC, indicate that replenishing stockpiles of several key missile systems will take years.
"It depends on the munition - but one to five years [to make a single missile] is the bottom line," said Mark Cancian, a retired Marine Corps colonel and senior adviser at CSIS. "And there's nothing you can do to speed that up."
Which weapons matter most?
The conflict relied on two broad categories of weapons: long-range missiles used to strike targets inside Iran and defensive systems designed to intercept incoming drones and missiles.
Among the most heavily used offensive weapons was the Tomahawk Land Attack Missile (TLAM), a long-range cruise missile fired from ships and submarines that can strike targets more than 1,000 miles (1,600 kilometres) away. It allows the US to strike hardened military facilities and command bunkers without putting manned aircraft in harm's way.
CSIS estimates that more than 1,000 Tomahawks were fired during the conflict. Each missile costs about $2.6 million (£2 million), and CSIS estimates the stockpile may not return to pre-war levels until 2031.
The Patriot missile system formed the backbone of America's air defences during the campaign. Designed to intercept aircraft, cruise missiles and ballistic missiles, Patriots were also repeatedly used against relatively inexpensive Iranian drones.
According to CSIS estimates, about 1,430 Patriot interceptors were fired from an estimated pre-war inventory of roughly 2,330. Each interceptor costs about $4 million, while many of the Iranian drones they destroyed are estimated to have cost between $20,000 and $50,000.
"It takes several years to produce a missile. If you put money into the system today, you wouldn't get a missile for three or four years. Sometimes even five," Cancian said. "What we're getting [now] are missiles that were funded in 2023."
The US also used the more advanced Terminal High Altitude Area Defense (THAAD) system, which intercepts ballistic missiles at higher altitudes and over longer distances than Patriot batteries.
According to CSIS estimates referenced by the BBC, between 190 and 290 THAAD interceptors were fired from a pre-war inventory of around 360. With only nine THAAD batteries operational worldwide—seven of them belonging to the United States—continued use on this scale could leave the US with fewer systems available to counter ballistic missile threats elsewhere.
That is why concerns over US munitions have quickly expanded beyond the Iran conflict. For military planners, the issue is not simply how many missiles were used, but how many would be available if another major crisis emerged before production recovered.
Why Taiwan and Ukraine are central to the debate
One reason the issue has attracted so much attention is its timing.
The Iran conflict comes just before what many US military planners refer to as the "Davidson window"—a period during which some believe China could become capable of launching an invasion of Taiwan. The concept stems from a 2021 warning by Admiral Philip Davidson, then commander of US Indo-Pacific Command, that such an invasion could happen within six years. Former CIA director William Burns later said China could be ready by 2027.
China has invested heavily in missile technology, including hypersonic glide missiles and large-scale drone swarm capabilities, including hypersonic glide missiles and large-scale drone swarm capabilities, while continuing to insist Taiwan is part of its territory.
Cancian described the current situation as a "window of vulnerability", arguing that the US may not have the depth of preferred munitions it would want if conflict broke out in the Indo-Pacific. According to the BBC, US officials also believe China has been closely studying how American air defence systems performed during the Iran war.
Others argue the conflict has strengthened US deterrence rather than weakened it.
"Weapons create deterrence, not merely because nations have them, but also because they demonstrate a willingness to use them," said Jacob Olidort, a former CIA officer and former adviser on Middle East policy in the Office of the Secretary of Defense.
He added that US "successes at eroding Iran's military capabilities with precision, with record time, send a signal to other adversaries, including China and their ambitions."
The same tension between supporting allies and preserving US reserves has already shaped Washington's approach to Ukraine.
Months before Operation Epic Fury, Trump declined to provide Ukraine with Tomahawk missiles, citing concerns about preserving US reserves. Ukrainian officials continue to say they urgently need Patriot systems and other air defences to counter repeated Russian drone and missile attacks.
"In addition to energy prices, it [the Iran war] means the depletion of US reserves, and the depletion of air defence manufacturers," Ukrainian President Volodymyr Zelensky told the BBC in March. "So we [Ukraine] have a depletion of resources."
Zelensky also pointed to the production challenge, saying the US manufactures roughly 60 to 65 missiles each month—around 700 to 800 a year—while 803 were reportedly used on the first day of Operation Epic Fury alone.
The Trump administration has since proposed allowing Ukraine to manufacture Patriot systems domestically, adding to similar arrangements already in place in Germany and Japan.
Former Pentagon official Elaine McCusker believes the wars in Ukraine and Iran could accelerate the development of cheaper systems capable of countering inexpensive drones.
"We've known for a long time that we don't want to be shooting $6m interceptors at $1,000 drones," she said. "I think we now have more focus on that solution, and more people focusing on manufacturing more attritable solutions that don't cost so much".
Is the US really running out of weapons?
Based on the available evidence, not yet.
While the US is not facing an immediate shortage of munitions, rebuilding advanced missile inventories remains a slow process measured in years rather than months.
White House spokesperson Anna Kelly rejected suggestions that the US faces an immediate shortage.
"The United States military has more than enough munitions, ammo, and stockpiles to serve all of President Trump's strategic goals and beyond, and Operation Epic Fury has exposed what happens when you mess with the United States," she said.
"Even still, the president has urged our defence contractors to constantly produce more made-in-America weapons," she added.
Iran, meanwhile, appears to face a far steeper challenge. Recent US military operations have focused on degrading Tehran's ability to threaten shipping through the Strait of Hormuz. According to the BBC, analysts believe repeated US and Israeli strikes have severely weakened Iran's capacity to manufacture missiles, drones and other weapons at scale.
Jason Brodsky, policy director at United Against Nuclear Iran, argued that Tehran is now directing its remaining arsenal towards what he described as its "trump card"—its ability to threaten the Strait of Hormuz.
"I think we have to realise that there are limitations there, and that the US has degraded their defence industrial base to a very significant extent," he said.
"The Iranian regime is running out of time here," he added.
Brodsky also argued that the current, manageable conflict with Iran has become the US military's "centre of gravity", even though ignoring the wider picture would be "irresponsible". In his view, policymakers have little choice but to prioritise immediate challenges. "The Indo-Pacific is a more distant threat right now," he said. "Policymakers have to prioritise, and the Middle East right now has the president's attention."
For now, there is little near-term alarm that the US lacks the munitions needed to meet its immediate military objectives. The bigger question is how quickly it can replenish advanced missile stockpiles that take years to replace. Every Tomahawk fired at Iran, every Patriot supplied to Ukraine and every interceptor reserved for a potential conflict in the Indo-Pacific comes from the same finite pool. Washington is betting it can manage today's conflict while defence manufacturers rebuild those stockpiles before another crisis demands them.
