On what date did the Soviet Union declare war on Japan in the final week before V-J Day?

The Soviet Union declared war on Japan on August 8, 1945.

Soviet Foreign Minister Vyacheslav Molotov informed Japan’s ambassador, Naotake Satō, in Moscow on the evening of August 8. The declaration stated that the Soviet Union would consider itself at war with Japan from August 9. Soviet forces then began their offensive in Manchuria shortly after midnight on August 9.

The timing fulfilled the Soviet commitment made at the Yalta Conference to enter the war against Japan within three months of Germany’s defeat. Germany’s surrender took effect in May 1945, so the Soviet entry occurred within the promised period.

A common date mix-up results from separating the declaration from the invasion. August 8 was the declaration date in Moscow, while August 9 was the date associated with the opening of the Soviet invasion and, in the United States, the Nagasaki bombing. Japan announced acceptance of surrender terms on August 15.