The Emergency Security and Tactical Hologram (ESTH) was a development from the Emergency Medical Hologram (EMH) and the extension Emergency Command and Conn Hologram (ECCH) concepts. It was part of the Emergency Holographic Complement of the fleet carrier classes and heavy battleship classes of Starfleet.
The ESTH was developed simultaneously with the Emergency Command and Conn Hologram in 2380, after tests have shown that the Tactical and Security departments of a Starfleet facility or starship could benefit from an emergency holographic program as much as a Starfleet sickbay or infirmary did with the EMH.
Essentially, the ESTH was a 'backup tactical officer' and 'backup security officer', intended to assume responsibility in maintaining the battle readiness of the ship and crew, in keeping order aboard ship, and in the maintenance, distribution and control of personnel weapons, such as hand phasers, and is expected to maintain proficiency in the use of each kind in the event that the current tactical crew would be incapacitated for some reason. The ESTH possessed over 2 million ship tactical and security subroutines from the operations databases of all the leading Tactical Officers and Security Officers in Starfleet, and could incorporate them into its plans in the performance of its tasks.
There were six (6) ESTH in the Emergency Holographic Complement of the fleet carrier classes and the heavy battleship classes of Starfleet and of Vanguard Command. In all other starships, there is only one (1) ESTH in the Emergency Holographic Complement.