Dave Saxton wrote:Steve Crandell wrote:Oahu's defenses were very strong from a military point of view, and the Japanese would not have had shore based air power with which to oppose them. Their only air support would have to have been provided by carriers, which were themselves vulnerable to air attack. Ships couldn't come close enough to provide shore gunfire support to an invasion because of the heavy shore batteries. Diamond Head alone was a significant fort, and there were others, including 16" guns. The latter were able to traverse 360 degrees, unlike the Singapore defenses. There were 360 degree heavy mortars in Diamond Head and other places. There were railway guns. This is not a push over, and the IJN would have been very far from home with no significant logistics capability. The US on the other hand had some aircraft which could be easily modified to self deploy from the US, like the heavy and medium bombers and the P-38 fighter.
The initial invasion would have been by far the most difficult part, and that ignores the resistance in the very unlikely event it would have succeeded.
The Japanese would probably establish an airbase and logistics center on one or more of the nearby islands (which would be relatively easy to take and hold) so they would not need to maintain a large naval task force in the area over an extended period of time. Meanwhile they would isolate and cut off US military forces and facilities throughout the Islands, and only later take Oahu when they are good and ready, only after establishing complete air superiority.
... Historically, complete air superiority was achieved as of Dec 7th 1941, 10:00hr.