Japan announces surrender and acceptance of the Potsdam Declaration
A little after noon, Japan standard time on August 15, 1945, Emperor Hirohito’s announcement of Japan’s acceptance of the terms of the Potsdam Declaration was broadcast to the Japanese people over the radio. Earlier the same day, the Japanese government had broadcast an announcement over Radio Tokyo that “acceptance of the Potsdam Proclamation [would be] coming soon,” and had advised the Allies of the surrender by sending a cable to U.S. President Harry S Truman via the Swiss diplomatic mission in Washington, D.C.
In his announcement of Japan’s surrender on August 14, President Truman said that “the proclamation of V-J Day must wait upon the formal signing of the surrender terms by Japan”. The formal Japanese signing of the surrender terms took place on board the battleship USS Missouri in Tokyo Bay on September 2, 1945, and at that time Truman declared September 2 to be the official V-J Day.
More info:
Victory over Japan Day
Victory in Japan (V-J) Day (History.com)