This is a really good question which came up in my last game and I just want to echo that I’d also love to hear an answer. In my game it was almost the opposite situation. I had a bomber in Hawaii that wanted to bomb 3 transports the Japanese player built in the Japan SZ with no other naval units. He had 2 Fighters and 2 Tac Bombers on Japan though and said he’d just scramble, I looked it up and we couldn’t decide on what the rules said, but we decided common sense dictated he could scramble and also reasoned he wouldn’t have put them there without naval proctection (and wouldn’t have left planes on Japan) if he thought they couldn’t scramble so we played it that they could.
Sorry I don’t have an asnwer though.