Why APFSDS is the wrong way to attack a submerged submarine

Would an armor-piercing fin-stabilized discarding-sabot round work for sinking submarines?

A direct hit could rupture a pressure hull, but getting a conventional APFSDS projectile to travel accurately through water makes it an impractical anti-submarine weapon.

A penetrator that struck a submarine's pressure hull could cause severe flooding; the resulting hole would be apparent from the incoming water. Delivering that hit underwater is the difficult part. Water entry changes the projectile's path and raises questions about fin stabilization and sabot separation. Making the system work would require extensive changes to a conventional APFSDS round. A surfaced submarine would still be vulnerable to the projectile's kinetic energy, and the penetrator's material could also cause a fire in the struck compartment.