German Saboteurs

Since the battle of the Marshall Islands, the Imperial Japanese Navy had completely lost the ability to ferry troops and supplies to the island of Borneo. What with the German fleets patrolling the South China Sea, and eliminating any Japanese vessels which dare to enter the region.

Meanwhile, the German wolf packs continued to harass Japanese shipping, and transport as far north as the Sea of Japan. Causing a massive headache to the Imperial Japanese Navy and Army alike. 

As a result, the only means of support the Japanese were able to give their troops on Borneo was via the Air. With their air bases stationed in the northern and southern Philippines, the Osaka Armory could pump out aircraft and hop them across the islands until they reached Borneo.