Not difficult. Interviewers that have already selected you just want to see your dedication in extracurriculars and your general confidence/demeanor during and interview. I definitely felt nervous since it was my first interview but it wasn't terrible. I just talked about my resume.
The interview process consisted of one behavior interview. During the interview, the interviewer asked both behavioral questions (like about work ethic, biggest failure), and technical questions about my past projects. There were no purely technical questions, like questions about beam bending.
Interview questions [1]
Question 1
Talk about one experience where you designed a product.
I applied through an employee referral. The process took 1+ week. I interviewed at Northrop Grumman (Chandler, AZ) in Apr 2021
Interview
Very quick and easy once contact with recruiters was made. Overall it was a smooth experience given the fact that I was interviewing and being recruited later than usual for internships.