Tornadoes and other fast jets don't have time or space for the pilots and other aircrew to use conventional lavatories; so they pee into a disposable `piddle-pack'. This is a plastic bag like a colostomy bag, strapped to the leg inside the flying suit, which is rubberized like a wet-suit. The bag has a plastic valve, and a sponge inside to prevent the urine from sloshing about.
Both the RAF and the USAF are having to think fast about providing for the female pilots coming into service.
See also aircraft.
If the users were unlucky and the waves were rough, a good deal of the sea came up through the holes. On ships as big as the Victory the heads were safer because they were high above the waterline.
The lavatories were called `heads' because the whole of the front of the ship is called the head. A rival theory that the sitter shouted `heads' to warn anyone below not to stick their head out of a porthole seems highly unlikely; there are never portholes in the extreme bows.