Say that some U.S. ally came under attack (we could say Ukraine getting attacked by Russia, although I don’t want to get too bogged down in specifics - any other nation would do, too.) And the United States, for whatever bizarre reason, decided to donate all sorts of military gear such as Abrams tanks, Arleigh Burkes, Apache helos, AC-130 gunships, even stealth fighters (hey, let’s even go further and say B-2 bombers, too) - …but without teaching the Ukrainians how to use any of it. The Ukranians are only accustomed to the existing warplanes, tanks, warships, etc. that they already have, which share no commonality with the gifted American stuff.
How long would it take the Ukrainians (or any other ally - Kurds, Jordanians, etc.), to master the stuff and put it to effective use in a war - or is the amount of stuff to be cram-learned simply way too much to overcome?