That reminds me of one source of mystery that's easily explained:
On modern US sub models you may notice an odd array of, well, something between the stern planes and the rudders. It has nothing to do with sonar or any other sensor. They are called "zincs" or sacrificial anodes.
All ships have to use what is known as a floating ground for electric systems. That, coupled with how steel reacts with salt water is the main reason why the hull below the water line HAS to be painted- the steel HAS to be isolated from the water or it will rust, heavily.
A steel hull will also generate its own static electric charge as it moves through the water, that charge can cause the hull to become magnetized as well as speed up rusting.
Zincs are placed on the hull because paint isn't perfect, it wears thin or chips off, and I guess the easiest way to describe what zincs do is to say that they look a lot more tasty to the sea water than the steel hull. Another way to think of it is to imagine yourself as the sea water (and you're always hungry), the hull as a plate of fried liver and onions, and the zincs as a slice of cherry pie.
Which one will you try to eat first?
