With USN subs around? A tanker full of gasoline and another full of aviation fuel going up before going down will certainly negatively affect the fuel supply available to the occupation forces. Remember Oscar and Charlie doing their windsurfing trip around Oahu? They came across a convoy just before it was attacked by a sub, and one of the ships hit was likely a tanker, though Turtledove describes it as a Maru (wartime slang for freighter), and one was a freighter.