I would think any military related installation would be heavily secured period. People would have to go through multiple security levels.
I would think getting a security clearance would be very difficult and anyone with an arrest would not get it, like Aaron Alexis. I know he does not have a criminal record despite being arrest a couple of times.
Have yourself another think, Ptarmy.
When I worked for the Naval Shipyard, so long as I had my badge out and displayed properly, and I looked like I knew where I was and what I was doing, I could get just about anywhere on base. Heck, even earlier than that, when I was but a wee pizza delivery lad, I was only one gate away from the actual ballistic missile subs at the Bangor Submarine Base most of the time. Were I of nefarious character
I could have taken advantage of the security situation in any number of ways, and I would have been far too deep inside the perimeter to have been stopped in any kind of timely manner.
This is not to say that the security folks aren't on top of things: while I was at the shipyard, they disappeared at least one scuba diver a month into the bowels of NID for being caught inside the security perimeter (usually with a camera, and usually just after a major combatant had come in for a refit) as one example where they were on top of things. All I'm saying is that most CONUS military bases are far to big an area for the security force regularly and normally employed on those bases to do anything but respond after the fact.