I&#x27;m only guessing, but it&#x27;s probably a nuance of the technology. The earlier weapons used cavitation created by the dart&#x27;s blunt tip to stabilize it and give it range below the surface. The last gun uses a gas bubble to create a <i>super</i>cavitation [1] effect, which based on my quick skimming of the linked Wiki article, seems to be more effective at greater depth.<p>Anyone with a more thorough (read: any) understanding of fluid dynamics is encouraged to correct or expand this.<p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Supercavitation" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Supercavitation</a>