Is Israel running low on missile interceptors? How long can it withstand Iran’s retaliatory attacks?

As the US–Israeli war with Iran enters its third week, reports are emerging that Israel is potentially running out of air defence interceptors due to Iran’s retaliatory attacks.

The Israel Defence Forces (IDF) and Israeli foreign minister have denied the reports. The government did reportedly approve around US$826 million (A$1.17 billion) for “urgent and essential defence procurement” over the weekend, however.

It’s difficult to gauge just how many interceptors are remaining, as the IDF does not disclose this type of information. But the possibility of this occurring was not entirely unexpected before Israel and the US began bombing Iran more than two weeks ago.

What are these interceptors?

Israel has a sophisticated and layered air defence system, capable of repelling attacks from ballistic missiles, cruise missiles, aircraft, drones and artillery shells at multiple altitudes, both inside and outside the atmosphere.

The famous “Iron Dome” makes up just one of these layers – it intercepts short-range artillery shells and rockets.

While there are technological differences between all of these systems, they are comprised of three basic elements:

• the IDF personnel to operate them
• the radar systems to detect incoming attacks
• the interceptors themselves.

Israel has a new “Iron Beam” laser system that can be used to destroy missiles and drones, but the most common interceptors are surface-to-air missiles.

Ballistic missile defence interceptors, in particular, are incredibly complex and expensive weapons. The more capable they are, the more expensive they are to build. They are also limited in number. A sustained attack can quickly deplete even Israel’s stockpile.

Why might Israel be running low?

The 12-day war that Israel fought with Iran last year significantly depleted both its stockpile of anti-ballistic missiles, as well as that of its ally, the United States.

One Washington-based research centre calculated that Israel and the US intercepted 273 of 322 Iranian missiles they attempted to stop in the war, an 85% success rate.

Given a large number of these interceptors were used so recently, Israel and the US are unlikely to have fully replenished their stockpiles before launching the current war.

Another sign this is the case: the US is reportedly moving parts of its THAAD missile defence system from South Korea to the Middle East. This means the US will need to carry more of the defensive burden in the region, which could quickly deplete its own assets.

Ballistic missiles are also very difficult to intercept due to the speed and altitude they attain. Several interceptors are usually required to ensure each incoming missile is stopped. Iran is also using cluster munitions on some of its ballistic missiles, which further compounds the problem.

Iran has cheap, easy-to-replace drones, which it is using to try to overwhelm Israeli and American air defence systems, as well. These can also be launched from dispersed locations that are difficult to detect, making them harder to destroy on the ground than ballistic missiles.

Iran has so far launched more than 500 missiles and 2,000 drones since the war began.

Jet fighters can help defend against these drone attacks and have done so with great success, but the missiles they fire are also more expensive than the drones themselves. And other weapons platforms (such as the Iron Beam) are currently in limited supply.

The US and Israel are not the only ones reportedly running low on interceptors. The Persian Gulf states have also come under Iranian attack, and are burning through what defensive assets they have.

The Iranians have specifically targeted missile defence radars across the region, with reports they have successfully destroyed or damaged several systems.

All of this, of course, raises the question of why Israel and the US would start another conflict in the first place if their stockpiles were not fully replenished. There could be several potential reasons:

• they had managed to rebuild their stockpiles faster than anyone anticipated, though this is unlikely

• they were confident they could destroy a sufficient amount of Iran’s offensive weapons before they ran out of defensive munitions

• they believed Iran would want to end the war sooner than it has.

How long can Iran keep this up?

There’s no way of knowing what Iran’s strategy is, besides extending the war as long as possible and creating chaos in the region and with global energy markets.

Some have speculated Iran may be deliberately holding back its more advanced missile technologies to use after the US and Israeli interceptors are depleted. But other analysts say there is no evidence this is the case. This would also be a risky strategy on Iran’s part.

One thing is certain, though: the US and Israel do have finite numbers of interceptors at their disposal. Iran, too, will not be able to keep up the same level of attacks indefinitely.

While the economic impacts of the war are placing significant pressure on all parties – and the world more widely – Iran seems to be in a better position for a longer conflict, given the costs involved for the US and Israel and their reluctance to commit to a potentially even more disastrous ground invasion.