Maybe a double question, but what harbor is the most well-defended/difficult to penetrate. Originally I was going to say Bergen, as it is labyrinth to navigate around, but then I woke up and realised that it is one of ours

I'm forever getting lost there.
But for me the most difficult to penetrate is Port Said. Not a difficult port to get into as such, but a lot of DD and torpedo boats there. Also it is extremely shallow so if you are detected, you have no chance to evade. Any other votes for different ports?