Japan and the Allies race to assemble their forces

Would Japan rush south before British and American forces learned to operate together?

Japan would have that incentive, but replenishment, other operations and the location of the Allied fleet would constrain how quickly it could attack.

Improving Anglo-American cooperation would give Japan a reason to attack promptly, but its ships would still need replenishment and reorganization after the Pearl Harbor operation. The Allied concentration would also take time, potentially extending from December into January. Britain could keep much of the force on the Indian Ocean side of Singapore while using the base's submarines farther forward. If Singapore and Malaya held, Japanese ships would face a longer route or a passage close to coastal guns and submarines. The naval contest would therefore remain tied to the land campaign. Better command and a rushed mechanized reinforcement are suggested as possible ways to stop the Japanese advance, without making that outcome certain.