This article provides an overview of the US Defense Department's organizations and command structure for defending unclassified networks. After briefly describing the relationships between the major organizations that conduct defensive operations, the article discusses some of the issues and problems the Defense Department faces in defending its networks and how it tries to solve them. These issues include fielding security patches, dealing with computer or network security incidents, and accurately reporting computer and network security breaches. The article ends by describing long standing shortfalls in the computer and network security areas that are of immediate concern to the Defense Department.