torpedo tube

 A tube fixed below or near the water line through which a torpedo is fired, usually by a small charge of gunpowder. On torpedo vessels the tubes are on deck and usually in broadside, on larger vessels usually submerged in broadside and fitted with a movable shield which is pushed out from the vessel's side to protect the torpedo until clear, but formerly sometimes in the bow. In submarine torpedo boats they are in the bow.  [Webster 1913 Suppl.]