There are two options I see to implementing the user interface for Point Defense:
After missiles are rolled and dice assigned, clicking done shows...
1. A single view that shows the results of the Point Defense cannon fire die roll and allows you to select dice/missiles to hit.
2. A preliminary view that shows you the intended dice to be rolled for cannon fire (this view would confirm the code is rolling dice appropriately). A secondary view that shows the same thing as #1 above.
#1 is simpler but involves some trust of the user. #2 Is slightly more user friendly for newer players and those who might wonder about the calculation of dice to be used for Point Defense.