Since you mention "second turret" do you mean the Weapon Able/Alfa mount?
The name stems from the change in phonetic pronunciation during the development of the weapon. There was a Weapon Bravo in collateral development, but was never deployed.
The Weapon "A" project was more of a 'directed depth charge' than a proper "hedgehog." At least in the sense of being a contact-exploding, spigot mortar-launched ASW. Hedgehog offered a number of advantages in attacking a submarine, but the primary one was in that they only created sound in the water if they made contact. That, and you did not have to go ahead full in the attack, as you would with conventional DC. Major downside was the lack of range, you needed to be able to get to within nearly "arm's length" of a sub to prosecute the attack.
But, such are the variables in Absurdly Slow Warfare <G>