Upon further exploration, it might be a bug. Port of Maffin has no naval transports in a campaign mode, see screenshots of campaign vs. scenario.
Also, couldn't win Wakde by destroying all enemy units. Checked the Japanese side in the scenario and seemingly destroyed all of them. Still, might have missed some unit.
Update: seems I missed some unit. Decided to cheat, disabled the fog of war, and got the brilliant by destroying all enemy units.