"Unified Command, as a part of the National Incident Management System (NIMS), was successfully used in the state-federal response to the catastrophic disaster caused by Hurricane Katrina in Mississippi in 2005. Four elements to determine the members of a Unified Command include: authority, co-location, parity and common understanding. Modifications made to ICS in the Mississippi response include extending the unified command concept down the chain to facilitate joint decision-making at all levels. Unresolved issues include the role of the Federal Coordinating Officer and Principal Federal Official, federal management of multi-state disasters, and the inclusion of components of the Department of Defense in a Unified Command."
Naval Postgraduate School (U.S.). Center for Homeland Defense and Security