As with any specialty, there are terms which are unique to any environment - and submarines are no different. As a subset of Naval terminology, sub have a twist of linguistics all their own. To add upon that, though not all transfer to a Steampunk subset, many do, as some below are listed (with their possible Steampunk associations in parenthesis)...
1-MC: The ship-wide intercom system aboard U.S. submarines.
(Steampunk translation - I'm confident that there would be some translation of inter-ship communications aboard a vessel, be it air or sea. So though it may not be a shipboard system run off of electricity, it would be an essential component of a ship. If the captain has to make a ship-wide announcement, it would be over a general announcing circuit.
One thought, still used to day is a "sound powered phone", which as one can see an interesting concept dating back literally decades. Some version of this might work, and the genre being what it is, pushing it back a bit further to the 1890's wouldn't be too much of a stretch, I'd say!)
Ballast Tanks: Large tanks are filled with seawater, which acts as weight, causing the submarine to lose buoyancy and sink. To surface, compressed air is pumped into the tanks, forcing the seawater out and restoring positive buoyancy.
(Steampunk translation - Physics are physics, and since the first implementation of a using a ballast system, I'd say it wouldn't have changed much, though it might affect the ship design.)
Battle Stations (aka, General Quarters): Areas throughout the ship which crew members man during engagements with the enemy. These may or may not be their standard assigned sections.
(Steampunk Translation - Conflict is essential to just about every story, and if a person is part of a ship's compliment, they will have a job to do, somewhere on the ship - navigation, gunnery, engineering, damage control, etc... If a person is a guest (aka - "rider"), unless they have an amazing skill, and are trained on a specific useful combat system, and have the Captain's blessing... they'll likely be sent to the mess decks, standing by to help in any way they can.)
Boat: Submarines were originally referred to as boats due to their smaller size. They are now as large or larger than many naval vessels and are considered ships. Generally a boat is a vessel that can be carried by a ship.
Bridge: On a submarine, the small observation area on top of the fairwater or sail.
Captain’s Mast: Session aboard ship at which the captain administers non-judicial punishment or commends outstanding performance.
(Steampunk Translation - Originally based on the "Rocks and Shoals", and after being consolidated with the other use forces regulations to become the "Uniform Code of Military Justice" (aka "UCMJ"), going to Captain's Mast is a big step down from a "Court Martial", and usually issued for lesser infractions at sea. They are usually decided by the Captain, and the accursed attends in their formal dress uniform. Also called "shooting pool with the old man", as the table the Captain and two officers in judgement sit behind a table with a green felt. Not a fun time.)
Head: An original naval term for a toilet. On olden ships (aka, wooden surface ships), it was at the "head" (forward bow) of the ship. No toilet paper, just salt water to be refreshed. Subs are a bit more civilized, but the "special" tanks need to be blown to sea, so they can be refilled.
Helmsman: Crew position from which the attitude within the water and direction of travel of the submarine are controlled.
OOD–Officer Of the Deck: An officer on duty aboard ship acting as the commanding officer’s representative, usually on the conn.
(Steampunk Translation - If the Captain isn't on the conn, the the OOD will have the conn. Usually, the OOD will be an experienced officer who has the CO's trust to run the ship while s/he is otherwise occupied)
Periscope Depth: The depth at which a submerged submarine can extend its periscope above the surface.
(Steampunk Translation - If you are looking out of a periscope at something, then you'll be at periscope depth.)
Periscope: Any one of several varieties of optical instruments allowing submarines, while remaining submerged, to view activity on or above the surface.
"Rig for …" : Command reference indicating that the ship needs to be placed in some specified condition as in “Rig for dive”.
Rudder: A movable waterfoil attached to the stern of a ship, used to determine the lateral direction of travel of the ship.
Sail: The streamlined conning tower protruding from the top of a submarine.
Screws: The technical term for a ship’s propeller.
Sea Mount: An under-sea mountain.
Watch Section: The officers and men on duty in a specified area constitute the watch section for that area.
XO–Executive Officer: Second in command of a naval vessel. The XO is responsible for the day-to-day operation of the ship while the captain keeps track of the “big picture”. Usually s/he has to be the hatchet-man/bad-guy/ass hat who enforces things the CO wants happen (e.g. field days, watchbill modifications, other unpopular decisions). Thankless job, and a precursor to eventually taking command of a ship.
(These were culled from the following location:
http://blastmagazine.com/the-magazine/sidebar/silent-steel-glossary-submarine-terms/, with the "Steampunk analysis" appended by my own observations and thoughts)!
For a few more casual terms, I've included a listing from the "Author's Den" - many of which I would certify are still in use!...
DINK- A person who is not progressing in his submarine or watch station quals.
MANUVERING WATCH- Stationed when the sub in leaving or coming into port. This watch puts the best crewmen is the right place.
NON-QUAL- A person who ha yet to earn his Dolphins
NUB - A new unqualified member of the crew. Having just been through boot camp and sub, or nuke school they still have very little hair.
RACK - A bed on the submarine. This might even be on top of of under a live torpedo. Usually very cramped - like a coffin.
There are quite a few not mentioned here, but do apply to RL Submarines!)