Papa Foxtrot Mike

[Intel Source: SubSim] The Navy files patents the same as any other organization; earlier this month, they were issued one (#7,206,257) that should be of great interest to submariners. (If the link above doesn't work for you, there's a copy of the patent here, or click here and search for the patent number: 7206257.) Here's what the invention is said to do:

A method of generating a predetermined field of cavitation around a remote target in an underwater environment, said method comprising the steps of: identifying a remote target in an unconfined underwater location; generating at least two acoustic beams from an underwater acoustic source; and controlling said at least two generated acoustic beams to intersect with each other at said identified remote target location and whereby a cavitation field is created at said intersection...
...it is an object of this invention to provide a self-defense weapon utilizing acoustic remote cavitation.
Another object of this invention is to provide an underwater self-defense weapon mounted on an underwater support vessel.
Still another object of this invention is to provide an acoustic remote cavitation weapon by generating an array of intersecting acoustic beams.
A still further object of the invention is to provide an acoustic remote cavitation weapon deriving power from an underwater support vessel and generating an array of intersecting acoustic beams at a long range.
Yet another object of this invention is to provide an acoustic remote cavitation self-defense weapon for generating a destructive cavitation in free water space.
In accordance with one aspect of this invention, there is provided a method of generating a predetermined field of cavitation around a remote target in an underwater environment. The method includes the steps of identifying a remote target location, generating at least two acoustic beams, each at a peak power output, from an underwater energy source, and controlling the generated acoustic beams to intersect with each other at the remote target location and thereby create a destructive cavitation field at the intersection of the beams.

The patent comes with drawings, too; here's one of them:

Looks pretty sweet. There's more on this over at Wired, where the commenters point out that there will be lots of opposition to deploying this new tool because of perceived danger to marine mammals. I'm guessing that we'll have to wait for Republicans to get back in charge of Congress before we get to deploy this system.