The Améthyste is a nuclear-powered attack submarine of the French Navy, the fifth of the Rubis type. Her name is a pun on a precious stone (Amethyst) and the acronym AMElioration Tactique, HydrodYnamique, Silence, Transmission, Ecoute ("Tactical, hydrodynamics, silence and transmission improvements"). She is the first vessel to serve in the French Navy under that name. She is a major upgrade upon the initial design of the Rubis type, and earlier units have since been refitted to meet her standards.