ships). The purpose of the program is to provide professional investigative, counterintelligence, and force protection support to deployed Navy and Marine Corps commanders. These special agents are assigned to aircraft carriers and other deployed major combatants. Their environment can best be described as a "floating city." The assignment offers many of the same investigative challenges found by any criminal investigator working in a metropolitan city. A special agent assigned to a carrier must be skilled in general criminal investigations including: crime scene examination, expert interview techniques, and use of proactive law enforcement procedures to stop criminal activity before it occurs. The special agent afloat also provides guidance on foreign counterintelligence matters, including terrorism. It is also the mission of the special agent afloat to offer Navy and Marine Corps leadership advice and operational support on security issues which might threaten the safety of ships, personnel and resources. The Special Agent Afloat (SAA) program was initiated in Europe during March 1967. In April 1971, a special agent was assigned to a deployed carrier for a period of six months with the designation of SAA. By 1978, SAA personnel were assigned to each operational aircraft carrier in the U. S. Navy for a one-year assignment. In 1986, a trial began where two Special Agents Afloat were assigned to aircraft carriers in an effort to determine the feasibility and effectiveness of having two agents assigned full-time while deployed, one focusing on law enforcement/criminal investigations and one on foreign counterintelligence. The trial was discontinued when no longer considered viable. Protective operations The Naval Criminal Investigative Service is the only entity within the Department of the Navy authorized to conduct protection of Department of Defense/Department of the Navy (DOD/DON) High Risk Billets (HRB). The mission of the NCIS Protective Operations Field Office (POFO) is to prevent terrorist and/or criminal attacks on principals under NCIS executive protection coverage and execute the necessary and appropriate response to a threat and/or attack on a principal. POFO will also initiate investigations on individuals and groups who meet a specific threshold when a threat is detected or needs to be validated. NCIS provides and manages full-time protection details on key Department of the Navy personnel, including: Secretary of the Navy Chief of Naval Operations Commandant of the Marine Corps To supplement POFO's operational mission, it maintains an internal Protective Intelligence Unit (PIU) to identify potential threats that could affect a