Why Did the US Bomb Japan Nearly 3000 Kilometers From the US Mainland and Not on German Civilians?

Dungar Singh Johan says why did the US bomb Japan nearly 3000 kilometers from the US mainland. Dungar: "The justification for the nuclear bombing, the nuclear tests on Japanese civilians is that it helped America end the war early" The Australians probably don't have the know-how of how to operate the submarines so most likely even the crew will be American. So it's America parking five or six nucleus of marines on Australian soil and Australian waters and Australia will pay the Americans for the privilege.