I need help here! (spoilers)

I watched this movie last night on Encore Action or one of those channels. I'd seen bits and pieces of it before but last night I thought, great, I have time to sit down and watch the entire movie.

And then, at the end, I got a phone call that I had to take and I missed most of the last few minutes of the frigging movie!

I saw the woman pick up the book on Shakespeare and look at it and then, phone rings, and the next thing I know, the "captain" is on deck about to shoot the woman, then shoots himself, and the survivors are rescued.

So the subs real captain was the ghost, right? He was murdered and wanted revenge, right? But if Bruce Greenwood and the other two officers had killed him why did he take his revenge on most of the rest of the crew too? From the flashbacks I saw they had nothing to do with it. And also why did he let the few crewmembers who survived survive? Did I miss something that explained that?

And was there a German U-boat sunk next to the hospital ship too? I thought I saw one...

Anyone?