The Nereiades is a classified as a deep-sea assault ship, a warship in the Imperial Navy. Although its weaponry level isn't very high, it is a small vessel that moves through the depth of the ocean at high speed to conduct patrol, enforcement, and reconnaissance. Its interior space isn't large, even for a warship.
It has black sails and an electric propulsion system that utilizes the solar power of photoelectric cells affixed to its wide mainsail and is so great that the ship maintained ample speed notwithstanding strong headwinds.
There were forty crewmembers in all.