They wouldn't be pursuing this, though, if there weren't some technical means available to suppress cavitation noise -- "Prairie Masker" used air bubbles to suppress propeller cavitation, although it didn't do anything for mechanical blade vibration. Streams of air bubbles around the vehicle might be what they're looking at.
There was a previous thread about a year or more concerning this project.
I must have been sleeping during the explanation of how cavitation is in regards to how it effects the actual efficiency of a craft moving through the water...
I was of the impression that water bubbles surrounding a moving surface reduce the efficiency of that surface...
Thus more fuel is needed to compensate for whatever speed advantage these goobers are thinking they'll gain...
Its alot like air moving across a propeller or wing surface...Anything that is attached or moved across the wing or propeller is consiedered parasitic in nature, thus the "parasitic" drag coefficient comes into play...
I believe the hydrodynamic environment has similar qualities...
I may be wrong but if Northrup Grumman is working this, either I am mistaken or the reporting of this issue is about 180 degrees out...
I'm betting that I may be partially wrong...
BTW, the "Prairie Masker" system worked great...All the subs had to do is track the "rain" sounds...It was almost transient in nature (thats what usually confused the operators)...
But for the most part it worked pretty good...We had it on our ship...