The problem is that my invading naval force tries to defend my attacking "marines", however, sometimes an enemy destroyer pops out from no where and kills the unit.
This had perplexed me on occasion as to how this could happen. Especially since I utilize a defence with my navy where the only gaps would cause the enemy unit to move past my defence in an adjacent fashion, thus losing any remaining moves.
I have since worked out that the unit usually is within the city I am attacking and that I cannot see it because they are hidden/covered by a land unit in the city.
What is the best way to see the destroyer or any other units in the city when the rule of having multiple units on a hex is allowed?