Why are Underwatert Explosions More Effective?
The fact is that bombs that explode underwater cause a much greater amount of damage than bombs that explode in air. When a bomb explodes in air, a great deal of the energy of the bomb is used to heat the air. Air is a gas and very compressible. As it is compressed, it heats up and less energy is used to cause the shock wave that causes the damage.
Water is very incompressible. Very little energy is there used in compressing water when a bomb explodes in water and a higher proportion of the energy is used in generating the shock wave.