[HtotheNootch]

Shadow Divers by Robert Kurson. I cannot recommend this book enough. It's the story of a group of divers who discover a U-Boat off the NJ coast. Two divers in particular become obsessed with identifying the boat, since nobody knows what it is, and there supposedly aren't any sunken U-Boats in the area.

I've probably read it 5 times or better. It's that good.