For the first part of the war, depth charges were the main weapon used against submarines by Canadian and Allied warships.

Depth charges (top) were cylinders packed with explosives. They could be dropped into the water from rails on the stern of warships, or fired over a ship's side from throwers like the example seen here. After sinking to a pre-set depth, the charges exploded with the aim of destroying the submarine with their shock waves. Requiring experience and considerable luck for their effective use, they had to be detonated within a few metres of the submarine's tough hull to have any effect.

Depth Charge, Mk VII
Depth Charge Thrower, Mk IV
CWM 19590025-001