When torpedoes became practical anti-submarine weapons

When did torpedoes become viable anti-submarine weapons?

In the late 1940s; earlier successes occurred, but dependable use required homing technology and less reliance on luck.

Isolated wartime hits differ from a weapon system with a useful probability of success. At least one earlier torpedo attack on a submarine is recalled, although its details are unavailable from memory. Before the late 1940s, such successes contained a large element of chance. Practical homing weapons turned the torpedo into a repeatable anti-submarine tool instead of an opportunistic shot.