I have an active DoD security clearance and some SCI compartment tickets.
I first received a security clearance to work on NASA’s Manned Orbital Laboratory because “.”
I have had security clearances and need-to-know compartments ever since because my work was funded in part, or intended at least in part for, DoD use—regardless of where I was employed.
That includes my time on the CS and ECE faculties at CMU. It is not unusual for academic research to be funded by military entities, especially DARPA and the military branch agencies such as the Air Force Office of Scientific Research, the Army Research Organization, and many others. But it was (and remains) uncommon for a faculty member at CMU or any other university to have a security clearance.
I was the first cleared faculty member in CMU’s CSD and the second one in CMU ECE. Having a security clearance opened up my access to system and application information that greatly helped me and my research team address the problems our sponsors hoped we would solve. CMU (as other universities) has a “.” My classified research and its circumstances were deemed to qualify for allowing it.
(The research by one of my ECE Ph.D. students also was restricted by that policy because it was funded in part by a corporation with which we had negotiated in advance that certain information would be proprietary to them, but which did not interfere with his research and thesis.)
I sanitized classified information for my team. Just as I provided unclassified information to my group, I also created unclassified versions of my personal classified research results. An issue when one is doing classified work is that there has to be a DoD-approved classified facility, e.g., for performing classified work and for storing classified documents received or written. The Mellon Institute near CMU had a DoD facility security clearance and is identified in the Restricted Research policy as being an eligible environment for faculty to perform classified research.
When I finally retired from full time employment, I became a consultant full time for a number of years; independence from an employer opened more opportunities to understand military real-time problems. I retained my DoD security clearance (I have access to a cleared facility). I finally retired from consulting in 2019.