While there are simple US weapons that have been provided (things like TOW missiles, M777 howitzers, etc.) and a small handful of complex ones (the famous HIMARS) many of the weapons provided have actually been of Soviet manufacture- since the Ukrainians already know how to take care of and use them, it is easier to give them Polish MiG-29's that the Ukrainian Air Force already can operate than to spend months training everyone on how to take care of a F-16. (Though in the end, I don't believe the Poles ended up giving any MiGs to the UAF, that was the central topic of negotiations for some time.)

The current signals (UKR having low artillery stocks and US and other NATO countries inability to provide more, with Russians stocks also apparently low) have reminded me of 1915 in the First Big Mistake, when everyone had used up their prewar stocks of artillery shells, and waited to bring the factories online to make vastly more of them- the build-up to the mega-deaths at Verdun and the Somme. Hopefully we won't see that level of death in this war.