The Americans believed that the Japanese would fight them every mile of the way to the homeland and that American forces would suffer many casualties,
There is also the thought that America wanted to punish Japan for Pearl Harbour and also to warn the Soviets that they could be next if they became aggressive.
Yes they did because it killed many people
See atomic bombings of Hiroshima and Nagaski
"fat man" was the name of the atomic bomb dropped on Nagaski. "little boy" was dropped in Hiroshima.
Hiroshima and Nagaski
August 8, 1945 (two days after Hiroshima)
They are famous for being bombed by the United States atomic bombs
The official reason for dropping the bombs were that the casualties in taking the Japanese mainland would be unacceptable. I believe that bomb was a show of strength from Truman to Stalin. Which Stalin pointedly ignored
Little Boy was used at Hiroshima and Fat Man targeted Nagaski.
This was the only time atomic weapons were used against mankind. They were dropped on August 6 and 9 1945.
Those cities were never deployed. They stayed still even with the atomic bombs dropped over them.
President Truman.
1945