The first two paragraphs of a NYTimes article on getting Leopard tanks for Ukraine:
" Nearly a month after Berlin gave European allies permission to send German-made tanks to Ukraine, the flow of tanks so many leaders vowed would follow seems more like a trickle.
Some nations have discovered that the tanks in their armory don’t actually work or lack spare parts. Political leaders have encountered unanticipated resistance within their own coalitions, and even from their defense ministries. And some armies had to pull trainers out of retirement to teach Ukrainian soldiers how to use old-model tanks."
I particularly laughed at the second sentence: maintenance is always problematic, particularly in armies which haven't fought wars.