Q-ship

A Q-ship is a merchant vessel that has been fitted with concealed weapons and disguised to appear as an ordinary unarmed civilian ship, used by Britain and its allies chiefly during the First World War and to a lesser extent the Second. The intent was to lure an attacking submarine into surfacing to sink the apparently defenseless ship with its deck gun, at which point the Q-ship's crew would drop disguised panels and open fire at close range. The tactic sank a number of German submarines and, more significantly, forced enemy submarine commanders to treat any merchant ship as a possible threat, changing how submarines attacked merchant shipping for the rest of the war.