Are your spies visible to the other players? when you enter their territory can they see you and then would naturally send a unit to stop you or you are invisible and if captured but someone it was just their luck that they sent troops to that square.
Are subs visible to everyone or just if you have a sub or cruiser close do you see the other guys' sub?
Are subs visible to everyone or just if you have a sub or cruiser close do you see the other guys' sub?