You don't need to get rid of every member of the CS who works with MoD. Many are doing valuable jobs which need to be done even when the military have picked up arms and gone off to perform their primary role.
You DO need to not be shy about getting rid of those who are "imbecilies - proper morons - as thick as mince, and getting paid for work they were not capable of doing."
You DO need to ensure that the Terms of Reference for CS are compatible with the environment in which they will be working and the military personnel they will be working with and for.
There is plenty of scope for reducing the size of the civil service without working those remaining until they drop.