I think there is an accepted informal 7 year from service time limit. But I agree that from the founding of DoD Congress did not wish a command military man as SecDef. A notion I agree with. The uniformed military is ably, ehh sometimes not, represented by the CJCS. We do not need to confuse the CoC by adding a career command level military man to the second highest rung in the CoC.
The DoD and the JCS are both bureaucratic nightmares of waste and stupidity. The SECDEF should be someone who hates waste and has an extensive understanding of the military with recent experience, and national defense. Most of the idiots (civilians, although there are some actual service members that don’t have a clue) within the DoD have no recent military experience and are so full of themselves.
I don’t know, it just seems like the SECDEF should have some (a lot of) familiarity with how the military works.
Otherwise how does he know whether or not his branch secs are feeding him a load of crap?
The CoC takes care of the whole ‘Civilian Control’ thing, so why shouldn’t the SECDEF be military? Otherwise couldn’t you also make the argument that the branch secs should be non-military too?