Having been stripped of most heavy equipment and experienced formations, its forces had an average efficiency of under 30 percent relative to prewar units.

The Japanese force tasked with defending Manchuria, the Kwantung Army, had been reduced from the Imperial Japanese Army's premier fighting force to a shell of its former self. The Japanese were thus being taken by surprise when the Soviet attack actually began on August 8. The Japanese monitored the buildup but did not believe the Soviets would be ready to attack until mid-September. To meet that deadline, the Soviet Union and the Western Allies co-operated in stockpiling supplies in the Far East, and the Red Army dispatched additional forces along the Trans-Siberian Railway. In February 1945 at the Yalta Conference, the Soviet Union under Joseph Stalin agreed to enter the war against Japan within three months of Germany's defeat. Nevertheless, the Japanese defenders at Mutanchiang achieved their goal of allowing the main forces to escape. Though casualties on both sides were heavy, the Red Army forces were able to break through the hastily organized Japanese defenses and capture the city ten days ahead of schedule. During the action, elements of the Japanese Fifth Army attempted to delay the Soviet Fifth Army and First Red Banner Army long enough to allow the bulk of the Japanese forces to retreat to more defensible positions. The rapid conclusion of the Manchurian campaign meant that this was one of the only set-piece battles that took place before the end of hostilities.

The Battle of Mutanchiang, or Battle of Mudanjiang, was a large-scale military engagement fought between the forces of the Union of Soviet Socialist Republics and the Empire of Japan from August 12 to 16, 1945, as part of the Soviet invasion of Manchuria in World War II.

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