Simeon Bourgeois' Torpedo Shell

Origin
Simeon Bourgeois (1815 - 1887) was a 19th-century French Navy vice-admiral who was involved in the development of early submarines. When he was captain he presented the project for the submarine Plongeur with Charles Brun. In 1860 the Plongeur would be the first submarine to be propelled by mechanical (by opposition to human) power. Later in his life, from 1870 to 1872, while Bourgeois was Commander of the Naval Division of the Western Coasts of Africa when he launched the first program to develop torpedo boats in the French Navy.

Effects
When submerged underwater or attached to a submarine, it allows anything attached to it to survive extreme depths. If the shells aren't polished every two months, the surrounding area can drop in barometric pressure making it feel like the bottom of the sea floor.