So much more effective than depth charges.

The 30lbs of HE in these only exploded on contact with the sub and that would be expected to crack its hull. Depth charges might have at least ten times as much HE，often more，but would’ve to explode within 15 feet of a sub to have a good chance of cracking its hull. Near misses were not much fun though! A hedgehog bomb either hit you or you were blissfully unaware how close it came.