It was the first time a nuclear weapon was used on a city in anger, and only one of two times, the second being 3 days later on Nagasaki, see this post

It is particularly poignant now, as observed in earlier posts, since the beginning of NATO’s war in Eastern Europe in February 2022 with the regular mention by its Warlords of using nuclear weapons which are today literally thousands of times bigger than the Hiroshima one, and which would result in much of civilisation looking like this — see this post.