What happens if a ground unit uses normal ground movement to enter a hex that is an enemy controlled port that with only an enemy ship in it? Does this become a battle hex? One rule states that the player gains control of the hex immediately upon moving into it if there are no enemy ground or air units in the hex. This would make it seem to me that it is not a battle hex but then again another rule says that any hex containing both offensives and reaction player units must be declared a battle hex and emergency naval move does not occurs until the end of the offensive.
The simple answer is follow the sequence of play (6.2). The ground unit enters the port and it changes control. Since there is no air or land units, the moving ground unit, if it has remaining MA can move on. If it is still in the hex during the battle declaration step, then there it becomes a battle hex. If there is a battle and the ground unit has no air or naval support, the enemy unit in the port fires at the ground unit, apply results. At the conclusion of battles, if the naval unit is still alive it makes an Emergency Naval Move.