Stocks of Terminal High Altitude Area Defense (THAAD) air defence interceptors have been reduced by up to 80 per cent, CNN reported this week. The Pentagon has also burned through two thirds of Patriot air defence missiles, according to analysis from the Center for Strategic and International Studies (CSIS). Shortages are being felt far beyond the US, which supplies Patriot systems and munitions to many of its allies. Other types of air defence systems cannot easily plug the gaps. But for now, air and missile defence remains a serious concern for militaries around the world – whatever Trump might say.