This definition appears in the opening credits of season 1; The Naval Criminal Investigation Service [NCIS] is a worldwide federal law enforcement organization whose mission is to protect and serve the Navy and Marine Corps and their families. To counter the evolving threats NCIS has implemented a new proactive strategic plan which emphasizes the following priorities; -Prevent terrorism and related hostile acts against DoN forces and installments -Protect DoN systems and information against compromise -Reduce criminal activity and mitigate the impact on Navy and Marine Corps operational readiness