Q-ships were essentially u-boat traps. They were merchant ships armed with concealed weaponry, designed to lure u-boats close enough to mount an attack, at which time the Q-ship would itself attack the u-boat. The Royal Navy commissioned a handful of them during WWII as did the US after their entry into the war.
The Q-ship mod adds them to the game. In RL I don't believe any of them had any notable successes, and the Q-ship programs of both navies were abandoned before war's end - but in the game, they can be a lot of fun...
...if your idea of fun is to put an eel into what appears to be a lone merchant, then surface to finish it off with the gun, only to have them start firing on you before you can get your own crew on deck. It's an eye-opener, that's for sure!
