Active ASDIC displaced passive listening during the 1920s

When did active ASDIC supersede passive hydrophone detection?

During the 1920s, especially as reliable fittings and trained crews became sufficiently widespread by the middle of the decade.

The transition came broadly during the 1920s as the Royal Navy gained confidence in active sound detection. ASDIC appeared around 1920, but useful numbers were not fitted and exercised until roughly 1924-25. Passive listening therefore gave way gradually. System reliability and operator familiarity had to mature before active detection became a fleet practice. Possessing a new device was only the beginning of building an operational capability.