This thesis describes the Defense Data Network (DDN) and its possible applications for the Naval Security Group. It reviews the background and historical information that contributed to the selection of DDN as the primary long distance data communications system for the Department of Defense. It evaluates some of the advantages and disadvantages of packet switching technology. The survivability, availability, and security features of DDN are presented. Also included are specifications of the hardware equipment, software standards, and operating procedures for DDN. The Naval Security Group does not require direct DDN access to accomplish its operational mission. There are, however, a number of nonoperational requirements that could be facilitated by direct DDN access. This thesis discusses a potential role for DDN in the Naval Security Group. Applications for administration, personnel, supply, and logistics functions are provided. Theses. (jes).