Not a homemade submarine story but very much related. When my dad was a teenager he saw a film by Jacques Cousteau, one of the coinventors of the first aqualun

Not a homemade submarine story but very much related. When my dad was a teenager he saw a film by Jacques Cousteau, one of the coinventors of the first aqualung and became obsessed with the idea. He lived on a smallholding and had been taught to be self-reliant, so by borrowing his dad’s welding gear he made himself a home-made aqualung. But how to test it? On the smallholding there was a water reservoir that was deep enough but when he tried it of course he had positive buoyancy so kept floating to the surface. Normal divers have a weight belt, but my dad decided to chain himself to a heavy wooden railway sleeper and just throw it in. So there he was, dragged to the bottom of the reservoir, chained to a railway sleeper with a semi-functioning home-made underwater breathing apparatus. He must have escaped somehow but when he told the story he would just leave that part a mystery and he’s dead now so there’s no way of finding out.