24/Counter Terrorist Unit
These smaller divisions are made up of "investigative agents, intelligence agents, undercover operatives, crack tactical squads for major raids, and special agents to oversee unit activities" according to 24: The House Special Subcommittee's Findings at CTU. The actions of a group of CTU domestic units are watched over by CTU Division Control. Division is generally considered to be an extremely bureaucratic organization that is brought in when Jack Bauer steps over the line or when the situation calls for greater control. As domestic units are controlled by Division, divisions are controlled by CTU District Control, which oversee a greater area of the country. District getting involved in a situation is extremely rare, and mainly exists for the coordination of Division.
As of season 5, CTU has been folded into the Department of Homeland Security after a large portion of their staff was killed in a terrorist attack on the headquarters itself. What this means for the organization and effectiveness of the organization itself is unknown, but it is presumed that there will be no signficant changes on the local level.
There have been several fictional accounts set in the 24 universe in the form of both novels and comic books. Although the canonical value of these books is questionable, they do shed some light onto the nature of CTU. One of those books, 24: The House Special Subcommittee's Findings at CTU, defines the organization as such:
- Counter Terrorist Unit (CTU) - Elite branch of the Central Intelligence Agency. The Counter Terrorist Unit operates domestic counterterrorism divisional headquarters in major U.S. metropolitan areas. The purview of the CTU is to investigate the activities of domestic or foreign terrorists inside America's borders and to prevent terrorist attacks. CTU divisions are made up of investigative agents, intelligence agents, undercover operatives, crack tactical squads for major raids, and special agents to oversee unit activities. CTU is specifically set up to coordinate activities with the Federal Bureau of Investigation, the Justice Department, and the Secret Service as well as local authorities. As a branch of the CIA, CTU operations are overseen by both Congress and the Executive Branch of the federal government.