Repetition is not our friend. Others here have said the ship was used against German U-boats. Which is it?
The germans did not call them Q-ships, and they did not use them against submarines. Theirs were commerce raiders. They would fly whatever flag would get them closest to the enemy merchant ship, then drop the false sides, and order the victim to heave to. If they did not heave to, or if they used their radio, the raider would open fire.
The crews of these ships were well trained and highly efficient. The men were hand-picked, and the ships were modified for combat in extreme secrecy.
These ships were used very effectively in both WWI and WWII. In WWI, Raider Wolf carried a folding seaplane for recon, which was the first use of this kind of technology. The seaplane was named "Wolfchen", or Wolf Cub.