What is the Patriot missile system and why are supplies depleted worldwide?

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...