> creaking of the bulkheads One of the counterintuitive features of submarines is that they're not built to be waterproof at the surface. The various parts of

> creaking of the bulkheads One of the counterintuitive features of submarines is that they're not built to be waterproof at the surface. The various parts of the hull aren't welded shut and instead rely on the external pressure to press them shut at depth. Making them waterproof at the surface ends up making them less able to resist the pressure at depth.