The Mark 9 is designed to clandestinely approach enemy vessels while submerged, surface to fire torpedoes, and then escape unnoticed. As such, its design incorporates stealth characteristics, including a lower profile and sonar absorbing materials. The Mark 9 SDV was intended to attack ships in shallow coastal waters that full-size submarines could not enter, and to draw attention of an enemy fleet away from the Mark 9's parent submarine. Though it proved very effective in exercises, the Mark 9 was retired starting in 1989 and was fully phased out of service by the mid-1990s due to manpower and budget constraints and because all of its capabilities save launching torpedoes were duplicated by the Mark 8.