[JMHawkins]

The ships you see in enemy ports are the ships that are based there between turns, but as Strider said, you don't know where those ships are actually headed. A large force of Japanese ships at Truk might be headed off to invade Guadalcanal, or Palmyra, or they could split up to patrol several Japanese bases. They will probably be headed for somewhere in South Pacific, but you don't know exactly where.