USA, by the command of President Truman to stop the World War II.
There was no battle per-se, in those cities of Japan, the US drooped atomic bombs resulting with the end of the war.
The Germans did not drop an atomic bomb on Japan or on anyone. It was the US which dropped two atomic bombs on Japan (specifically on the cities of Hiroshima and Nagasaki) in 1945.
Hiroshima - August 6, 1945 (Monday) Nagasaki - August 9, 1945 (Thursday)
The United States which remained neutral in the war, entered it and at the end they drooped the atomic bombs ending the war.
After the second atomic bomb was dropped over Nagasaki, there were no more bomb drooped in war until the Korean war.
There two atomic bombs used against man kind. The Hiroshima bomb drooped on August 6 1945 and the other one dropped over Nagasaki on August 9 1945.
On August 6 1945 the first one was drooped over Hiroshima. On August 9 1945, the next one was dropped over Nagasaki. On August 14 Japan surrendered.
No, at no time have the Japanese ever had atomic bombs!
The US employed Atomic Bombs as a last resort. The first bomb's widespread aftereffects.
NM
20 kilotons
In the United States.