First used in the 1991 Gulf War, the US Patriot air defence system has seen demand spike sharply this year, with supplies of interceptor missiles depleted by Ukraine's war against the Russian invasion and the widening war in the Middle East.

Ukraine is urgently seeking more Patriot interceptors to defend against a nightly barrage of Russian ballistic missile strikes. But the Iran war has drained arsenals in the US and the Gulf, and some European countries are holding onto missiles they may need for their own defence.

Following are some details about the Patriot air defence system, one of the most advanced weapons in the US arsenal:

What is the Patriot system?

Patriot, short for Phased Array Tracking Radar for Intercept on Target, is a mobile surface-to-air missile defence system built by US weapons maker Raytheon Technologies (RTX.N) that can be used in all kinds of weather and at long range.

Developed in the 1980s, the Patriot system has been modernised over the past decades, expanding its capabilities and reach. It is slated to remain in service through 2048.

A typical battery includes radar and control systems, a power unit, launchers, and support vehicles. The system can intercept aircraft, tactical ballistic missiles and cruise missiles, depending on the interceptor used.

What can the Patriot system do?

The system has different capabilities depending on the type of interceptor used.

The earlier PAC-2 interceptor uses a blast-fragmentation warhead that detonates in the vicinity of a target, while the PAC-3 family of missiles uses more accurate "hit-to-kill" technology to physically collide with the target.

Raytheon makes the PAC-2 GEM-T interceptor, which can defeat smaller, short-range ballistic missiles, cruise missiles or enemy aircraft. Lockheed Martin (LMT.N), the world's largest arms maker, builds the more advanced PAC-3 Missile Segment Enhancement (MSE), which can hit longer-range ballistic missiles, cruise missiles, aircraft and also hypersonics.

In July, Lockheed introduced a new interceptor, the PAC-3 Adapted Capability Effector (ACE), which it says will cost half as much while still being able to target short-range ballistic missiles, aircraft and cruise missiles.

The system's radar has a range of over 150 km (93 miles) and can simultaneously track up to 100 potential targets, the North Atlantic Treaty Organization (Nato) said in 2015.

Although not originally designed to intercept hypersonic weapons, in May 2023 the US confirmed Ukraine had used the Patriot system to shoot down a Russian Kinzhal missile, which Moscow claims is hypersonic.

Countries closely guard details about the number of targets destroyed by Patriot systems, although Ukraine said in January it had destroyed 250 targets, including 140 ballistic missiles. Patriot has also destroyed dozens of Iranian ballistic missiles in the Gulf, although details have not been released.

How widely is it used?

Raytheon has built and delivered over 240 Patriot fire units, according to its website. Raytheon and Lockheed together have manufactured thousands of interceptor missiles.

Nineteen countries now operate the Patriot system, according to Raytheon, including the US, Germany, Poland, Ukraine, Japan, Qatar, Saudi Arabia and Egypt. Sixteen have the newest PAC-3 MSE missiles. Six to eight countries have requested additional missiles to replenish their depleted stocks.

How much does it cost?

A newly produced single Patriot battery costs over $1 billion, including $400 million for the system and $690 million for the missiles in a battery, according to the Center for Strategic and International Studies (CSIS).

Patriot PAC-3 interceptors are estimated at around $4 million to $5 million per missile.

Why are supplies dwindling?

Specific inventory numbers are classified, but CSIS estimates that about 65% of US Patriot interceptors were expended between February and July, with less than 850 left on hand, down from 2,330 before the Iran war began.

Current inventories in the Gulf states are also severely depleted, and several European countries have transferred some of their supplies to Ukraine, experts say.

Saudi Arabia used about 86% of its 2,800 PAC-3 interceptors in the first 38 days of combat, leaving it with 400 missiles left in April. Other Gulf nations used up similar amounts of their inventories, CSIS said.

Are countries buying more Patriots to boost inventories?

The US has approved the sale of 5,250 interceptors to Bahrain, Kuwait, Qatar, and the United Arab Emirates for replenishment.

The US is also pressing ahead with talks on allowing Ukraine to make Patriot interceptor missiles, even after President Donald Trump cast doubt on such a deal, sources familiar with the discussions said. The talks include an option for Ukraine to build some components for final assembly elsewhere in Europe.

Last month, the US Army awarded Lockheed Martin a contract worth up to $58.6 billion to produce Patriot interceptor missiles.