I could see changing this to one round to be like airbase attacks and strategic attacks if folks think that is what makes most sense. It my allow fleets to have more longevity with only one round of port bombing.
It may make Pearl Harbor fell a bit better too. If the Japanese have to retreat their planes after one round of bombing, the US would still control the sea zone. As the rules work now, it is the Americans that have to retreat, leaving the Japanese in control of the sea zone (and making Hawaii out of Supply for the Spring turn) which always kind of bugged me. . .