Following an informal discussion with a student at work - were the WWII nuclear bombings of Hiroshima and Nagasaki war crimes?
Caveat 1: By your standards, not international law at any given time.
Caveat 2: No, not a poll, this is a highly nuanced argument which doesn't benefit from "click a button yes/no".
Me? I tend toward yes. I get the arguments against e.g. demonstrating the weapon in an unpopulated or military-only area, but not convinced.