A depth charge is an anti-submarine warfare (ASW) weapon. It is intended to destroy a submarine by being dropped into the water nearby and detonating, subjecting the target to a powerful and destructive hydraulic shock.

How effective are depth charges?

Modern depth-charge launchers are computer-controlled mortars that can fire 400-pound (180-kg) depth charges in patterns 2,000 yards (1,800 metres) away from a ship. Atomic depth charges are fitted with a nuclear warhead and have a vastly increased killing radius because of their great explosive power.

How close did a depth charge have to be to sink a sub?

About 15 feet or less. However, that would be for a single depth charge. Depth charges that detonate at greater distances can do non-lethal damage, however, several non-lethal explosions may cumulatively do enough damage to sink a sub.