GREP Expression Needed

I'm reposting this here, hoping some genius scripters will know more than the designers ---

I've scoured the websites and have been trying to figure out the correct GREP expression for what I'm trying to achieve, but to no avail, so alas I am posting this in hopes of ending my misery.

I want to add an italic character style to the names of Naval ships (USS xxx xxx) in my book.  I want to italicize the name, but not the 'USS'. Any ideas?

Thanks a million.

~Laurie