support the field office's subordinate units by dispatching experienced Special Agents and/or civilian investigators to assist in investigations if a prolonged investigation is required or the investigative resources required exceeds the subordinate unit's capabilities. Usually the senior-most Special Agent of the field team is designated as the Senior Field Agent who may also have some operational and/or administrative responsibilities. The geographic field offices are divided into NCIS Resident Agencies (NCISRA) and NCIS Resident Units (NCISRU). NCISRA's are headed by Supervisory Special Agents (designated as Resident Agents in Charge) who supervise all sworn Special Agents and civilian personnel assigned to the NCISRA. Depending on the size or location of the NCISRA, the Resident Agent in Charge may also supervise other Supervisory Special Agents who serve as team leaders, responsible for a specific investigative/operational function within the NCISRA (e.g. SSA of Counter-Terrorism). Some NCISRA's are further divided into NCISRU's, which are small units consisting of only one or two Special Agents (designated as Resident Agents) who report directly to the Resident Agent in Charge of the "parent NCISRA." In NCISRU's which are staffed by multiple Special Agents, the senior-most Special Agent is designated as the Senior Resident Agent and may also have some operational and/or administrative responsibilities. NCIS Special Agent Afloat duty posts are also classified as NCISRU's (e.g. NCISRU USS George H.W. Bush). NCISRU's afloat are under the functional supervision of the field office responsible for the vessel's homeport but receive operational support from the field office responsible for the area where the ship is sailing in. National Security Directorate The National Security Directorate has program management oversight of counter-terrorism/counterintelligence investigations and operations, including espionage, terrorism, compromise, technology transfer, cyber intrusion, insider threat, and threats to research development and acquisition programs. The directorate is also responsible for manning, training, and equipping of agency personnel to protect Navy and Marine Corps forces, operations, information, facilities, equipment, and networks from attacks and the intelligence activities of foreign governments and international terrorist organizations. The National Security Directorate is managed by an executive assistant director with the assistance of an assistant director. The directorate is divided into multiple programmatic departments which are headed by deputy assistant directors (comparable in practice to special agents in charge). The departments are further divided into divisions led by division chiefs (comparable in practice to assistant special agents in charge). In 2015, the National Security Directorate comprised (at least) the