[Emperor's Child]

If you want to have a retreat option, you almost need to be in simultaneous movement mode. Consider this: At the very end of your movement phase you move into a zone with an enemy ship. This enemy ship then has the ability to chase you out of the zone you occupied, and you could possibly retreat further ahead depending on the logic of where you retreated to. This would be tantamount to getting extra moves.

And from the other perspective, consider the possibility of an enemy coming in to your zone during his movement phase, and your ships retreat from them. He could just simply re-attack you several times, and when it was all said and done you could find your fleet significanty further away from where they started. So how much move would your fleet have to use? I guess you (ie: the computer) would have to just keep track of it and consider that as forced movement which would reduce your fleets own movement in your own phase.