Britain would have more nearby troops and ships available before later commitments in Europe and the Middle East drew them away. Forces could move from India, Australia, the Indian Ocean, the Mediterranean, and other imperial stations rather than only from Britain. Singapore would also have better-prepared local and jungle-trained troops. By 1941, deployments to Norway, North Africa, Iraq, and Iran, including protection of the Persian supply route to the Soviet Union, had already pulled forces away from the Far East. Those drains had not yet occurred in January 1939. Japan would be caught by the outbreak without the stockpiles, trained personnel, maps, and detailed planning assembled for the 1941 campaign.
Notable Point · 4:58-8:40
Malaya without a prepared Japanese campaign
An early war changes the Malayan campaign because Japan lacks the later invasion's stockpiles, training, mapping, and operational preparation.