The Forces have already done that with a civilianisation program a good few years ago. Many, many rear echelon jobs such as IT support, instructing etc have been turned over to either the Civil Service or contractors, thus releasing troops to the front line.
As an example of how successful it was - when my own IT Support job at Bovington went civi I was replaced by an EO and two AO's, thus raising the wage bill for the Garrison.
Not only that, but they decided my IT experience was too valuable to let go so created a Data Analyst job to keep me anyway.