I was recommended by a contact within the company. After I applied for the job, I was asked to do a phone interview. That went pretty well; the interviewer asked standard questions about my background and experience, and probed a little into my technical ability. A couple weeks later they asked me to come out to San Diego for an on-site interview. This consisted of 3 parts: A panel interview with 3 senior engineers, a 1:1 interview with the dept head, and a 1:1 interview with HR. The technical interview wasn't as challenging as I had anticipated; the rest were fairly straightforward.
I would recommend that people contemplating working here be willing to work many and long hours. NG does offer overtime for salaried employees from time to time, which is nice actually, but it is not guaranteed. And like most government contractors, be prepared for lots of paperwork.