Battleships from World War II were mostly tough and resilient, capable of taking several hits from heavy artillery and still moving sprightly, fighting like dragons for hundreds of rounds. However, if hit by a torpedo, they were mostly doomed.
This is because the power of shells in water is far greater than in air.
The main force of a bomb in air comes from the expansion of air. But when it explodes underwater, it also causes water to form an air bubble, and the destructive shockwave from this expansion is incredible.
The density of seawater is about 835 times that of air, and its ability to conduct force is countless times stronger than air. Additionally, air is compressible, but seawater is almost incompressible.
As a result, the force seems incredibly concentrated, and once it hits, the destructive power is astonishing.
Don't mention depth charges; even a small firecracker can explode fish underwater.
