A large portion of the Japanese Army is committed in northern China during the winter, facing or preparing to face the Soviet Union. Long and difficult lines of communication make those formations slow to redeploy south. That delay reduces Japan's ability to mount a quick attack on Hong Kong while Britain moves reinforcements through India, the Middle East, and Singapore. Army geography becomes a naval factor because it changes which ports and bases each side can threaten before fleets concentrate. This is a scenario judgement about January 1939 commitments, not evidence that a specific southern operation had already been ordered.
Notable Point · 38:43-39:20
Japan's northern army commitments slow a southern response
Troops committed in northern China and toward the Soviet frontier cannot rapidly shift across poor communications to attack Hong Kong or the southern colonies.