USS Scorpion Submarine
Evidence for a more mundane explanation comes from the sub's propeller shaft, Boyne says. Undersea photographs show it rests about 20 yards outside the wreck on the seafloor, about 11,220 feet underwater. Boyne suggests that rubber bearings holding the propeller shaft failed, putting stress on the coupling connecting it to the engine. The coupling's bolts failed catastrophically during a deep test dive, the theory goes, spilling water into the sub too rapidly to allow ballast maneuvers to raise the ship to the surface. Ref. Source 3