Grumman Tracker anti-submarine aircraft of the Royal Canadian Navy used practice depth charges like this one to help detect Soviet submarines.

Trackers carried several small practice depth charges in the two wing-mounted nacelles that housed the aircraft's engines. When detonated in the ocean, their explosive fillings created noise that travelled through the water. Reflecting from the hull of a submarine, these sound waves could be picked up by sensitive microphones called sonobuoys that were also dropped into the water. Equipment on board the aircraft would use the echoes to calculate the submarine's likely position.

Practice Depth Charge, Mk 15 Mod 12
CWM 20020045-2840