Just started playing SH3 this month and am on my third campaign. I scuttled the first two due to human error. Haven't any experience yet with the game, but I do know that opening fire on a destroyer in the straits south of Scapa Flow results in an unhealthy number of depth charges being dumped on my head. I did manage to hug the floor long enough to convince the destroyers (four of them total) that they'd done their job, but man that was a long scary wait.
Grats on the completion of your campaign, maillemaker.