Starting in mid-1943, Canadian escort vessels began to be equipped with the Hedgehog anti-submarine mortar, which fired groups of projectiles like this.

The Hedgehog shot 24 depth-bombs over 200 metres in front of a warship. The projectiles, which sank in a broad elliptical pattern, would explode on contact with a submarine's hull. The Hedgehog offered a major advantage over conventional depth charges because it allowed an attacking ship to track the targeted submarine with ASDIC (sonar) up to the moment of firing.

Projectile, Anti-submarine, Hedgehog
CWM 19680174-001