The cables are well-protected, but if they are damaged - same as with HV overhead lines - there is protection circuitry on both sides that trips and shuts off t

The cables are well-protected, but if they are damaged - same as with HV overhead lines - there is protection circuitry on both sides that trips and shuts off the power. So it will limit the damage to the rest of the grid, but you probably wouldn't want to be scuba-diving next to the cable when that happens.