Working on the steam catapults, you have two cylinders with a piston in each cylinder and connected by a bridge. WIth those pistons moving at 150mph+, there was an elaborate water brake at the end of the cylinders in order to prevent metal-to-metal contact.
A steel box forms the water resevoir, holding about 2,000 gallons of water. We had to perform maintanence and tolerance checks on the brakes. This required going through a hatch, into the unlighted tank holding a flashlight, with the water warmed up by all the steam and half an inch of industrial lubricant floating on the surface. You then passed through a bulkhead and climbed up into the brake assemblies, literally lying in the path of the pistons.
Prior to doing this check/maintanence, the procedure was to chain the shuttle/grab on the flightdeck to a padeye, rendering it immovable. But there were stories…and while you were in the water brakes you could hear movement on deck at all times. Sliding sound, shine light up cylinder…nothing. Continue working, dragging sound…look, still nothing.
One of my NCOs was on the Nimitz doing that maintanence, when someone unchained the grab and started the pistons forward. Dude rolled out just escaping getting squashed with a giant spear up his arse. Shook for like 10 minutes, then went looking for blood.