#031–How long have ships had “watertight compartments” & how were they developed?

I've had this question in the back of my mind since I became a Titanic nut around age 5. It's the mythology as much as the technology that keep me coming back to this piece of history. And the biggest question in my mind is, how did watertight technology develop and how was it tested? The Titanic's design always left me scratching my head.