Torpedoes and missiles kill in a fundamentally different way. Missiles impact the target (or in very close proximity) and explode producing concussive damage -

Torpedoes and missiles kill in a fundamentally different way. Missiles impact the target (or in very close proximity) and explode producing concussive damage - very effective against anything sensitive to pressure like personnel. However an appropriately armored target can be made to survive these explosions. Hundreds of kilograms of explosive can do quite a bit of damage, but ships weighing hundreds of millions of kilograms can be made to tank such hits. Modern torpedoes explode below a ship. This explosion creates a void of high pressure, low density steam in the surrounding much denser water. As this bubble rises due to bouyancy, the pressure difference causes it to expand. Eventually momentum causes it to over-expand, and the void collapses, creating an extremely high pressure region in the center, which re-expands. This keeps happening as the void keeps rising. If detonated at the appropriate depth, by the time it reaches the surface the bubble has expanded into a massive void comparable to the size of the ship. When it breaks the surface, the steam pressurizing it internally is released, and the void collapses rapidly. With the water underneath it's center suddenly gone, the ship's weight is now only supported on its ends, and it bends like an overloaded beam. Within fractions of a second, the water that rushed to the center of the void reaching extremely high pressures now takes the path of least resistance to rebound, which happens to take it straight through the most stressed part of the ship. This geyser acts like a waterjet, cutting right through the ship. On top of all this, for a well designed torpedo, those fluctuations of the bubble on its way up weren't random: the frequency of its cycles is close to the resonance frequency of its hull. Much like how a wine glass can be shattered by an opera singer hitting the right note, the ship is especially susceptible to energy delivered at its resonance frequency. The largest supercarriers may be too big to be sunk by a single conventional torpedo, but anything smaller will sink within minutes of a successful hit. Now to achieve these results, torpedoes are far more expensive than comparably sized missiles, and of course they have much shorter range and speed. Missiles are more versatile and for many purposes totally sufficient. But if you suspect a hostile navy is sailing towards your shores, a few torpedo boats in strategic chokepoints that can each take out any vessel in one hit might be game changing.