War Eagle/Joe
Would that former NPS instructor be named Jeff? If so he was still an eng when I saw him last. Good to see he is doing well. Worked with him at NPTU.
Firefox
Your trip to the sub base is just a chance to woo you into the program, not really to assess your application. Odds are, if they have already decided to spend the money for your travel, then they are taking you seriously. The folks at DC determine if you'll go the DC.
You'll get a MEPS physical to determine if your physically eligible.
Like War Eagle said, in DC you'll get 2-3 technical interviews based on your transcripts and a short job interview with Adm Donald. In technical interviews I was asked everything from the odds of rolling a total of 6 with 2 dice, to integration by parts, to shear/bending moment diagrams from statics. Depends on classes you've taken. Adm just wanted to know why I wanted to be in the program.
If accepted, you'll know right away and be sworn in right away before you can change your mind and waste everyone's time and money, so be sure you want to do this before you go.
All that being said, I vote for a line officer job over instructor duty which is for the most part a dead in job in the navy. Instructors are very intelligent but often get little respect. Usually the GPA req't for a NPS instructor is 3.8'ish though.
For what it's worth, line officer experience allowed me to step right into a civilian nuke job. The specific req't for an ops supervisor type job is 2 yrs as EOOW/EWS/RO or equivalent if being hired from outside the plant with no prior civilian nuke experience. Instructor duty wouldn't fit the bill.
Hope this helps
Good luck with whatever your decision.