Like all Naval vessels, the term used for a Submarine's bathroom is a "Head".
The term "Head", in reference to a ship's toilet, was used at least as far back as 1708 on sailing vessels. It referred to the location of the ship's toilet, then located at the bow, or head, of the ship, under the bowsprit. It was located there as it was naturally washed by the ocean spray coming over the bow. The nautical term head, referring to the front or bow of a vessel, dates back to the early 1400's.
On military vessels, the bathroom is called "the head". It is usually a tiny room large enough for one person and only with a toilet and sink. The shower is a separate tiny cell.
The submarine is manned by the crew, and crew members are called submariners.
The 'helmsman' steers a submarine.
Fulton designed a submarine called Nautilus.
The USN's submarine force in WWII was called the SILENT SERVICE.
The H. L. Hunley was the name of the Confederate submarine that was the first combat submarine to sink an enemy ship.
submarine
A submarine earthquake causes a tsunami.
Nautilus
bridge
fairwater planes
Periscope.