World War 1 - Q-Ships
Introduced towards the close of 1914 by the British and French - and later deployed by the Italian and Russians navies - Q-Ships were deployed as an initially although decreasingly successful anti-submarine weapon. Alternatively referred to as Special Service Ships or Mystery Ships, the purpose of Q-Ships was straightforward: to trap enemy (usually German) submarines.
https://www.firstworldwar.com/atoz/qships.htm