High Quality Content by WIKIPEDIA articles! In naval parlance, the sail (American usage) or fin (European/Commonwealth usage) of a submarine is the tower-like structure found on the dorsal (topside) surface of submarines. Submarine sails usually house the conning tower (command and communications data center), the periscope(s), radar and communications masts (antenna). When surfaced, the sail serves as an observation platform. Historically, much of the submarine control was performed from the conning tower located inside the sail superstructure, but some newer submarines can be controlled entirely from the bridge.