Break before starting Engineering Masters

[JRD]

I know that it's possible to get into a graduate program in engineering a few years after finishing undergrad, but I have kind of a unique situation. Right now I'm in the Army and it will be 4 years after I finished my mechanical engineering degree before I'd start a masters program. Is it generally unheard of getting into a graduate program with that time of pretty unrelated work? Would taking a night class or two in the meantime actually be useful in the application process?