Several japanese midget submarines were part of this operation. Had war already been declared, it's hard to imagine that this would not have prompted a major response. The fact that hawaiiis like a giant aircraft carrier all by itself makes it easier for the radar operation people to rationalize the many, many planes.
Deep themes run through this show, with allegations of Japanese war crimes and atrocities in China at the start leading to eerily familiar, almost modern questions over how the world should respond. And then Dec 7, 1941 arrives...