The US is amphibious assaulting Korea and can the planes in japan scramble to kill the transports in the seazone. The are no jap ships in the sea zone.
The scrambling fighters will defend the seazone, not the territory.
Yeah that would be hilarious to screw your teammates cause one forgot to bring beer over, which means as playing as the US I would buy infantry and anti aircraft guns to protect Alaska and my crab fishing grounds.