Why not try COGO?
Take some costly and ancient piece of kit, a Land Rover say. Contractor determines that a new fleet of Toyotas can be acquired and operated at a lower through life cost than the old kit.
The Service is responsible for maintenance and operation - we have an expeditionary force so we can deploy and maintain without having to start a new contract to have grey suits wherever doing the dirty stuff.
When cost basis changes the contractor changes the kit.