European theatre of World War II
The operation was carried out as a classic double pincer movement over an area the size of the entire Western European theatre of World War II. In the western pincer, the Soviet Red Army advanced over the deserts and mountains from Mongolia, far from their resupply railways. This confounded the Japanese military analysis of Soviet logistics, and the defenders were caught by surprise in unfortified positions. The Kwantung Army commanders were engaged in a planning exercise at the time of the invasion, and were away from their forces for the first eighteen hours of conflict.