Hey Chuck. I was a defense contractor for 15 years, and lived in Columbia, MD and the Lexinton Park area... which is why I have now moved back to Jacksonville, FL.
The schools in Calvert and St. Marys are equal, Charles and PG County have some really terrible teachers and administrators. Viewing the schools as equals, your next consideration should be traffic. Working at NAS and living in Calvert means a lot of time sitting in traffic due to delays at the bridge, which barring a 40+ mile drivearound, is the only for you to get home.
I lived in Lexington Park proper, and in Mechanicsville in the north of St. Mary's County, and I greatly preferred the later of the two. I had a 24-mile drive to work, but traffic on RT 5 is very light and there are multiple ways for you to get to and from the base. This location also puts you just about equally between your work, and Waldorf where the mall and most of your shopping is.
I have to tell you that I think you're nuts for moving from Florida. Your cost of living up in Maryland is going to be significantly higher than it is down here. Real estate is very expensive, and you're going to be paying state and county income taxes. Unless you're going to be making about 40% or more than what you're making in Florida, you're going to be putting yourself at a pretty significant risk.