This is nothing new, the process began over four decades ago. Back then, this was a hard sell, because the draft provided large numbers of cheap troops. Adjusting for inflation, your average draftee in the early 1960s was getting about $10,000 a year in pay and about that same again for room, board and medical care. But these young guys were generally untrained. So even then, the military found it cheaper to hire more experienced civilians, at higher rates of pay, to do things like run military bases. This involved everything from maintaining and repairing vehicles to clerical work.
In the 1950s, someone did the math and discovered that it was cheaper to hire civilians for menial jobs that the enlisted troops had traditionally done, like helping out in the kitchen (KP) or yard work (policing the area), if the troops in question already had a full schedule of military duties. At first, this applied to troops attending technical schools (electronics or other equipment repair and maintenance) or who were performing technical jobs. In the past, it had often been the practice to exempt many of these troops from menial tasks, so they could keep the trucks, tanks, radios and radars operating. But the other troops who had to cover for the exempt guys were not happy. Through the 60s, it dawned on more and more commanders that soldiers, no matter what they were paid, were better soldiers if they spent all there time doing what they were trained to do.
This became more of an issue when the draft disappeared in the early 1970s, and soldiers pay more than doubled to attract enough volunteers to keep the ranks filled. But, like barnacles on a ships hull, over the years there is a tendency for more and more non-military jobs to get filled by troops. It takes someone at the top to come along and shake the tree, as it were, to get many of the uniformed people out of the civilian jobs. In the next two years, the Navy will hire 2,648 civilians and transfer about the same number of sailors to jobs civilians cannot do. The Marines will do this with 2,116 people, the Army 10,968, and the Air Force 4,338. The army has the largest number of people being transferred out mainly because the army has been doing this sort of thing internally for several years, moving troops out of support jobs (and often eliminating the job) and putting the those soldiers in combat units.
The Department of Defense has decided to replace over 20,000 military personnel with civilians in the next few years. Actually, there wont be any firing of troops. The new civilians will allow the uniformed personnel to be transferred to uniquely military jobs. The new civilian employees will replace troops doing stateside, civilian type, jobs.