Keep in mind that's likely not related to the dB sound pressure level in air that we're all familiar with. dB is a logarithmic ratio to pressure to a reference. In air, that reference is 20µPa, acoustic pressure in water typically uses a different reference (1µPa). There is also an adjustment of 36 dB to account for the higher impedance of water. So 235 dB in water is roughly 173 dB SPL -- still loud, but many orders of magnitude lower.
The only saving grace is that they only use it as a last resort since sending out that kind of noise would let everyone in that hemisphere know exactly where you are.
Oil and Gas exploration in the sea routinely uses extremely loud sounds, because explosive geosensing. Its screwing up cetacean migration and mating. It travels miles and miles.
Usually it is surface ships which get that loud. In harbors where sabotage is a concern it is not uncommon to run a regular ping as a deterrent to underwater saboteurs.
