If you mean Hedgehogs (HH) which you can launch at subs, theyre normally found at the very bottom of the list of guns.
7x 7.2" Mark 11 Projector (for premium HH)
5x 7.2" Mark 10 Projector (for normal HH)
Put them on T slots with any gunner and they can launch explosive anti-sub mines that detonate a few seconds after they hit the water. But the reload time is very long.
If you want actual depth charges (which drop into the water right next to your ship) then you need the torpedo launcher named Mine Launcher and some mines which you buy for olives. They can only be used on FF, DD and CL.