Earlier quoted context omitted.
Yes, clearly. If you slam into the water at Mach 6, there won't be anything left of you weapon more than a few meters down.
Interesting question: is it possible to build something capable of hypersonic speeds which can survive a surface impact and go straight into supercavitation? Alternatively, how deep do you have to go to escape the damaging effects of the shockwave from something slapping into the surface of the sea at mach 6?
As to how deep... not that deep, especially for a boomer.