In Mission window select the mission. Then on the sub screen is 
the sub you have to use cause the arrow keys are in active and 
the player can pick any sub. Well if you put the mouse cursor on
the sub name and press tab, the arrow that was in active turns 
red. The player can then take the mouse and click on the red arrow
that is now active and pick any sub from the list making it player's
choice instead of computer choice.