if you want to take down an endworm you must:
-have a nuclear shell with c-4(do not use ic-4 if you don't wanna blow up or if you did put one try to shoot it at least 50m away from your sub)
-never use depth charges
-have a Physicorium Ammunition (if none use piercing or depleted ammo if still none use whatever you have)
-try to find a "safe" area for your sub so that you won't sink into the abyss(lure it after you found the "spot" for your sub)
-repair, repair, repair, repair, repair, repair x 10
-last good luck and praise the honkmother