Our only function is the Protection of Critical Infrastructure vital to the United States. The Department of Homeland Security has identified (16) critical infrastructure sectors whose assets, systems, and networks, whether physical or virtual, are considered so vital to the United States, that their incapacitation or destruction would have a debilitating effect on security, national economic security, national public health and safety, or any combination thereof. Presidential Policy Directive 21 (PPD-21); Critical Infrastructure Security and Resilience advances a national policy to strengthen and maintain secure, functioning, and resilient critical infrastructure.