"A torpedo-vessel or other submarine vessel of cylindrical form or approximately cylindrical form having a screw-propeller applied in the usual way is very liable to roll on its axis in the water, owing to the action of the screw-propeller, and when rudders inclined in an upward and downward direction are employed on such a vessel for directing its course up or down in the water such rolling or turning of the vessel, by producing a lateral inclination of such rudders makes the liable to divert the vessel from its proper course; to which end the invention consists in the combination, in a torpedo-vessel or other submarine of side rudders for directing the vessel up or down in the water and two screw-propellers of opposite pitch arranged side by side rotating in opposite directions and intermeshing, the axis of said rudders and screw-propellers being all in the same transverse plane."