Complex sentence: It was subordinate to the Japan Defence Army until August of 1945 when the Soviets Red Army launched Operation August Storm when it was transferred to the Kwangtung Army, where it didn't see combat.
Split into simpler sentences: It was subordinate to the Japan Defence Army until August of 1945 when the Soviets Red Army launched Operation August Storm. Then it was transferred to the Kwangtung Army but it didn't see combat.