The United States officially observes September 2 as V-J Day for Japan's World War II surrender.
September 2 is the date on which Japanese representatives signed the surrender instrument aboard USS Missouri in Tokyo Bay. President Harry S. Truman designated the date as the official V-J Day in connection with the formal signing of the surrender terms.
August 15 is also strongly associated with V-J Day because Emperor Hirohito's surrender announcement was broadcast in Japan on that date. Because of time-zone differences, the announcement was heard on August 14 in the United States. The United Kingdom observes August 15 as its official V-J Day.
These different dates explain why historical sources sometimes list more than one V-J Day. The distinction is between the public announcement of Japan's acceptance and the later ceremony that formally signed and implemented the surrender document.