In coalition military operations, secure and effective information sharing is vital to the success of the mission. Protected Core Networking (PCN) provides a way for allied nations to securely interconnect their networks to facilitate the sharing of data. PCN, and military networks in general, face unique security challenges. Heterogeneous links and devices are deployed in hostile environments, while motivated adversaries launch cyberattacks at ever-increasing pace, volume, and sophistication. Humans cannot defend these systems and networks, not only because the volume of cyber events is too great, but also because there are not enough cyber defenders situated at the tactical edge. Thus, autonomous, machine-speed cyber defense capabilities are needed to protect mission-critical information systems from cyberattacks and system failures. This paper discusses the motivation for adding autonomous cyber defense capabilities to PCN and outlines a path toward implementing these capabilities. We propose to leverage existing reference architectures, frameworks, and enabling technologies, in order to adapt autonomous cyber defense concepts to the PCN context. We highlight expected challenges of implementing autonomous cyber defense agents for PCN, including: defining the state space and action space that will be necessary for monitoring and for generating recovery plans; implementing a suite of models, sensors, actuators, and agents specific to the PCN context; and designing metrics and experiments to measure the efficacy of such a system.