Battle of Lake Khasan ( July 29 — August 11, 1938) was an attempted incursion by the Japanese into the territory of the USSR.

The conflict started on July 15, 1938, when the Japanese attaché in Moscow demanded the removal of Soviet border troops from the Bezymyannaya (высота Безымянная) and Zaozernaya (высота Заозерная) Hills to the West of Lake Khasan in the south of Primorye, not far from Vladivostok, claiming this territory by the Russia-Korea border. The demand was rejected.

The first Japanese attack on July 29 was repelled, but on July 31 the Soviet troops had to retreat. Under the command of the chief of the Far East Front , Vasily Blyukher, additional forces were moved to the zone of conflict and after several engagements during August 2-9 the Japanese forces were pushed off the Soviet territory.

On August 10, the Japanese attaché asked for peace and the hostilities ceased on August 11.

This incident has been mostly unnoticed in the West, since the initial aggression of Japan in Asia has traditionally not been counted into the World War II. This battle was the first defeat of the Axis powers. However Soviet losses were significant, and the Japanese military, while taking the lesson seriously, was willing to engage with the Soviets once more, in 1939 – see Battle of Halhin Gol.