What is the cause of dishing of shell plating above the waterline during a nuclear detonation?

Dishing of shell plating above the waterline during a nuclear detonation is primarily caused by the intense pressure wave generated by the explosion, commonly referred to as the blast. When a nuclear device detonates, it creates a rapid expansion of gases that results in an extremely powerful shock wave. This shock wave exerts an immense amount of force on any structures in its path, including the shell plating of ships or other vessels.

The phenomenon of dishing refers to the deformation of the metal plating, which can curve inward or become concave due to the blast's pressure. The energy from the explosion is sufficient to cause significant structural changes, particularly in materials that aren't designed to withstand such forces.

While other factors, like underwater shock or water waves, can also have damaging effects on ships or structures, they typically do not result in dishing of the above-water shell plating to the extent that a blast would. Nuclear radiation, while dangerous and damaging in many ways, does not exert the mechanical forces needed to cause this type of physical deformation directly. Thus, the blast is the most critical factor in the case of dishing.