The same geographic logic that made it a "must" to attack the PI
...would have mandated an attack on the Soviet Far East as well, but the Japanese military rationalized not doing so.
The Philippines were indeed adjacent to the shipping lanes carrying oil and other supplies from Southeast Asia, but US forces in the Philippines were limited, far from reinforcement, and not capable of impeding Japanese attacks on European colonies. Relatively minor re-routing, for instance, running most South China sea shipping through the Taiwan Straits instead of the Luzon straits, could protect Japanese shipping pretty well in the early forties.
The Soviet Far East was even more proximate to the Soviet homeland, and more chock full of hazardous Soviet ground, air and naval forces than the Philippines was. If US air power or subs in the Philippines were an unacceptable threat, than consider the threat of Soviet airpower against shipping between Korea and Japan. While these lanes were not Japan's oil lifeline, they were its lifeline for troop redeployment from the home islands and imports of foodstuffs and metals from Northeast Asia. The geography of the Soviet position posed a greater threat of bombardment of the Japanese homeland, or interference with Japanese forces in Asia, than the relatively small capability the US had in the Philippines.
...would have mandated an attack on the Soviet Far East as well, but the Japanese military rationalized not doing so.
The Philippines were indeed adjacent to the shipping lanes carrying oil and other supplies from Southeast Asia, but US forces in the Philippines were limited, far from reinforcement, and not capable of impeding Japanese attacks on European colonies. Relatively minor re-routing, for instance, running most South China sea shipping through the Taiwan Straits instead of the Luzon straits, could protect Japanese shipping pretty well in the early forties.
The Soviet Far East was even more proximate to the Soviet homeland, and more chock full of hazardous Soviet ground, air and naval forces than the Philippines was. If US air power or subs in the Philippines were an unacceptable threat, than consider the threat of Soviet airpower against shipping between Korea and Japan. While these lanes were not Japan's oil lifeline, they were its lifeline for troop redeployment from the home islands and imports of foodstuffs and metals from Northeast Asia. The geography of the Soviet position posed a greater threat of bombardment of the Japanese homeland, or interference with Japanese forces in Asia, than the relatively small capability the US had in the Philippines.