A stabilizing fin for damping the rolling motion of a ship and which extends and stows athwartship. The stabilizing fin is rotatably mounted on a fin support axle which is slidably mounted in a fin chamber located athwartship in a ship''s hull. The stabilizing fin is extended into its operative position and retracted into its inoperative position by a threaded shaft cooperating with a nut mounted to the fin support axle. When in operative position, the stabilizing fin is tilted by actuation of a cam which imparts rotary motion to a fin tilting arm attached to the stabilizing fin. The stabilizing fin is extended, retracted, and tilted by means of hydraulic actuators. The hydraulic system for supplying hydraulic fluid to the hydraulic actuator for extending and retracting the stabilizing fin includes solenoid-operated and pilot-operated valves such that the hydraulic actuator is only supplied with pressurized fluid when the stabilizing fin is properly positioned for fin extension and retraction. The hydraulic system for supplying hydraulic fluid to the hydraulic actuator for tilting the stabilizing fin includes servo and pilot-operated valves such that the hydraulic actuator is only supplied with pressurized fluid when the stabilizing fin is in the fully extended position. A novel servo valve for use in the hydraulic system for controlling the supply of hydraulic fluid to the hydraulic actuator for tilting the stabilizing fin is also disclosed.