Analysts estimate about 850 US Tomahawk missiles have been fired during the Middle East war. (US Navy via AP)
In short:
The US is estimated to be burning through high-end weapons at a rapid pace in its war on Iran and stockpiles could take years to replenish.
Analysts say the weapons may not be available for use should other conflicts break out.
They say the duration and outcome of the war could be affected by which side runs out of critical weapons first.
The United States went into war with Iran with full force, unleashing some of its most advanced and expensive weapons.
In the first 16 days of the conflict the US burnt through 11,294 munitions at a cost of about $US26 billion ($38 billion), according to estimates from the Payne Institute for Public Policy.
It estimated more than 5,000 were fired in the first 96 hours alone.
With the war entering its fifth week and the possibility of a US ground invasion not ruled out, American allies have raised concerns about dwindling supplies.
On March 19 Armin Papperger, chief executive of major German arms manufacturer Rheinmetall, warned global stocks of missile interceptors needed for air defence systems were "nearly empty" as a result of the US-Israel war on Iran.
A building that was damaged by an Iranian drone attack in Manama, Bahrain. (Reuters: Hamad I Mohammed)
Analysts say weapons pressures could end up affecting the duration of conflict, with sizeable holes already blown in high-end munitions stockpiles.
They predict it could take years for some supplies to be replenished, making US allies "nervous" about the West's military readiness for other potential conflicts.
Neither side backing down
US President Donald Trump has given Iran several ultimatums, threatening to escalate attacks if a deal to end the war is not reached.
But Tehran has repeatedly rejected the proposals, saying the terms were "unrealistic" and issuing its own threats.
Amin Saikal, emeritus professor of Middle Eastern studies at the Australian National University, said the negotiating demands put forward by the US and Iran were "worlds apart".
As it stands, the scene could be set for a much longer war.
"So far both sides have displayed the capacity to be able to confront each other," Dr Saikal said.
"At this point, neither is willing to really back down."
[Pete's Lecturer/Tutor at Australian National University in the early 1980s] Amin Saikal does not think the war will be ending anytime soon. (ABC News)
He said if the war dragged on for several more weeks, the side that lost the most "hardware" could start pulling back.
"Whichever side depletes its stocks of missiles and interceptors first could signal a desire to end the fighting," Dr Saikal told the ABC.
US burns through crucial weapons
In early March Mr Trump boasted the US military had enough weapons stockpiled to fight wars "forever".
But recent estimates from the Payne Institute paint a different picture.
Analysts from the research centre at the Colorado School of Mines have been tracking daily weapons exchanges since about day five of the Middle East conflict.
Based on available data on prewar stocks, it assessed that the US had lost nearly 46 per cent of its Army Tactical Missile Systems (ATACMS).
The surface-to-surface missiles have a range of up to 300 kilometres and were designed to strike high-value targets such as missile sites.
The institute estimated supplies of Terminal High Altitude Area Defense (THAAD) missile systems, used by the US and its partners in the region to defend against Iranian missiles, were also dropping significantly.
Projections showed the THAAD interceptors could run out by mid-April.
Data from the Payne Institute for Public Policy estimating the use of critical weapons from March 24 and the dates of possible depletion. (ABC News Graphics/Payne Institute)
Jahara Matisek, a command pilot in the US Air Force and senior fellow at the Payne Institute, said only about 100 THAAD missiles were made a year.
"Our tracking system has tracked about 200 to 400 of those being used at this point, so how do you replace that?" he said on ABC Radio National Breakfast.
THAAD systems are being used extensively by the US and its partners to defend against Iranian missiles. (AP: US Air Force/Cory Payne)
Israel's Arrow 2 and Arrow 3 interceptors, used to take out Iran's powerful longer-range missiles, were also projected to be exhausted by the end of March.
Retired Marine Colonel Mark Cancian, a senior adviser at the US Center for Strategic and International Studies (CSIS) defence department, said the Payne Institute's data provided "a good estimate".
But he said it was impossible to know exactly how many weapons were in each side's stocks before the war broke out on February 28.
"If Israel was really about at the end of their Arrow missile inventory, I think we would be hearing reports that they wanted more Patriots [air defence systems] or another THAAD deployed to Israel," Colonel Cancian said.
"We haven't heard that."
Damage in a residential neighbourhood in southern Israel following a night of Iranian missile strikes. (Reuters: Ilan Rosenberg)
Tomahawks, Patriots in short supply
Colonel Cancian was not surprised that a modern conflict would burn up a lot of munitions in a relatively short time.
But he was shocked to see some critical weapons had been fired in such large numbers.
"Particularly Tomahawks and Patriots," Colonel Cancian told the ABC.
"These systems are a problem because they are in short supply and high demand."
Tomahawks have a range of about 1,600km and can be launched from land or sea.
The missiles are used to strike deep-territory targets with precision, without sending pilots into dangerous airspace.
A Tomahawk is fired from a US vessel in the early days of the Middle East conflict. (US Navy — Wikimedia Commons)
Only a few hundred Tomahawks are manufactured a year and cost about $US3.6 million ($5.2 million) per shot.
The US fired about 850 in the first month of the war, more than in any other military campaign in history, the CSIS estimated.
Colonel Cancian did not believe the Tomahawk stockpile would be completely depleted in the Middle East war, but there were concerns about whether enough supplies would be left to protect other regions.
"What's making people very nervous is a potential conflict with China," he said.
"In the Western Pacific, a US ship can stay well away from China and still be able to launch this missile at Chinese forces."
Expensive US Patriot defence systems are being used to defend against cheap Iranian drones. (AP: Sebastian Apel/US Department of Defense)
It was a similar situation with Patriot air defence systems, which the US and Gulf states were using to intercept Iranian ballistic and cruise missiles.
The Gulf states' Patriot interceptors in particular were at risk of running dangerously low, according to Payne Institute data.
Lieutenant Colonel Matisek said there were also reports of "very wasteful intercepts" using Patriot missiles, which cost about $US4 million to shoot down $US50,000 ($72,000) drones.
"If current munition burn rates keep occurring … it means you just run out of everything and now you can't support Ukraine, you can't defend Taiwan in a future crisis," he said.
Ukrainian President Volodymyr Zelenskyy warned that Kyiv would "definitely" face shortages of Patriots because of the US war against Iran.
Lockheed Martin produces about 600 Patriot PAC-3 interceptors a year.
The Payne Institute estimated about 402 were fired in the first 16 days of the war on Iran.
Iran's weapons not quite 'obliterated'
Before the war, it was estimated Iran had thousands of missiles and drones stockpiled in underground facilities.
It has been using those supplies to wreak havoc on its US-allied Gulf neighbours in waves of retaliatory strikes.
Mr Trump claims the US has "obliterated" Tehran's military abilities, after striking more than 10,000 targets in Iran.
But Jonathan Panikoff from the Atlantic Council's Middle East program said that did not appear to be the case.
"They are still managing," he told ABC News Daily.
Iran's missile capabilities had been "significantly diminished" but "certainly not obliterated", he added.
"Not to mention the thousands of drones Iran still has in its inventory," Mr Panikoff said.
Jonathan Panikoff says Iran could have plenty of firepower left. (Supplied)
Lieutenant Colonel Matisek said Iranian drone and missile attacks had fallen by 80 to 90 per cent from their initial peak, but were still straining US and Israeli defences across the region.
He said Iran's capabilities might have been underestimated.
"The ability for the Iranians to sustain the fight likely reflects they had way more [weapons] stockpiled," Lieutenant Colonel Matisek said.
"This is really troubling … because the US interceptors, the missiles that shoot down missiles and drones, those are running critically low."
Supply chain strains
Whether the US weapons stocks continue to hold up could be determined by the intensity of prolonged fighting.
"We could go into a new phase where there's ground combat — not on the mainland, but maybe on the islands," Colonel Cancian said.
"If we go into that, it's possible there may be strains on parts of the inventory, such as the Patriots, if the Iranians really let loose with whatever they have left."
Lieutenant Colonel Matisek said weapon production rates were already a major concern and that the White House would be looking for an off-ramp.
He said it could take at least five years to replenish 500 Tomahawk missiles and that there were wider supply chain issues to consider.
China controls many of the rare earths and materials needed to make a wide range of weapons.
Patriot air defence missile systems can cost millions of dollars. (AP: Mindaugas Kulbis)
Lieutenant Colonel Matisek said the US was already receiving F-35 fighter jet parts with missing radar components.
"We suspect it's because of Chinese export controls over germanium and gallium," he said.
"We do not have the supply chain … to replace a lot of these munitions."
A limited supply of minerals was not an issue you could "just throw money at", he added.