While other allies, including Germany, have recently promised to provide more Patriot air defence systems, the US is the only producer of interceptor missiles they fire.

Spare parts for Bradley fighting vehicles and barrels for M777 howitzers also have to come from America.

As well as promising more military aid, the US confirmed it would increase the number of military advisers posted to its embassy in Kyiv, prompting jeers from the Kremlin, which said that the US risked tripping into a military quagmire.

Maria Zakharova, a spokesman for the Russian foreign ministry, said: “Washington’s deeper and deeper immersion in the hybrid war against Russia will turn into a loud and humiliating fiasco for the United States such as Vietnam and Afghanistan.”

Franz-Stefan Gady, an associate fellow at the International Institute for Strategic Studies, said that the aid gave Ukraine breathing space for trying to solve the even bigger problem of replenishing its battered army with more soldiers.

“The new aid package also gives Europe some temporary breathing space to ramp up air/artillery ammo production and launchers,” he said. “We should see a noticeable increase in European industrial output in late autumn or winter.”

That points to the deepest vulnerability in Ukraine’s war effort.