日ソ中立条約
Due to the Soviet–Japanese Neutrality Pact, the Soviets made it policy to intern Allied aircrews who landed in Soviet territory following operations against Japan, although airmen held in the Soviet Union under such circumstances were usually allowed to "escape" after some period of time. Nevertheless, even before the defeat of Germany the Soviet buildup in the Far East steadily accelerated. By early 1945 it had become apparent to the Japanese that the Soviets were preparing to invade Manchuria, though they were unlikely to attack prior to Germany's defeat. In addition to their problems in the Pacific, the Japanese realised they needed to determine when and where a Soviet invasion would occur.