|Caption:||T'Pol in 2155|
|Wearing a sciences division outfit that was found aboard the Defiant.|
Lieutenant commander T'Pol was a female Vulcan who served in the Starfleet arm of the Terran Empire. She served as the second officer on the ISS Enterprise and occasionally acted as the ship's science officer. T'Pol resented being thought of as a slave, and often voiced her opinion, whether someone asked for it or not. (ENT: "In a Mirror, Darkly" ) Prior to January, 2155, T'Pol had entered pon farr, and had Charles Tucker III do her a "favor", which he enjoyed. (ENT: "In a Mirror, Darkly" ) T'Pol was promoted to first officer of Enterprise when Commander Jonathan Archer mutinied against Captain Maximilian Forrest. This was despite the fact that Archer was highly prejudiced against Vulcans, and that Major Malcolm Reed was next in line for that position in the ship's chain of command. This was because Archer believed that Reed, while being a capable soldier, had trouble following orders; Archer also had respect in T'Pol's capabilities as an officer and a scientist. Archer had also erroneously believed that he had her support and loyalty. (ENT: "In a Mirror, Darkly" ) T'Pol and other Vulcans secretly formed a counter-mutiny against Archer to put Forrest back in command of the ship. To assist in returning control of the Enterprise to Captain Forrest, T'Pol tempted Tucker with a sexual encounter so that she could mind meld with him, planting a mental suggestion to sabotage the cloaking device on Enterprise, and then had his memories altered. When Commander Archer later briefed the senior crew regarding the ship the Tholians had obtained from the future of the mirror universe, and his plan to seize it, T'Pol was skeptical and objected to the plan. Forrest overruled her objections and proceeded with the mission. When Forrest ordered Archer to take an assault team aboard the Defiant, he pulled T'Pol aside and secretly ordered her to kill Archer during the mission. T'Pol never got a chance to carry out the order.
While the assault team was on board the Defiant, the Enterprise was attacked and destroyed by Tholian vessels. With T'Pol's help, Archer and the assault team managed to power up the Defiant, escape the Tholian base and destroy their ships.
After the Enterprise's escape pods were collected by the Defiant, there was a crew complement of only 47, not nearly enough to run a Constitution-class vessel on a long-term basis. Furthermore, the ship was not fully operational in that the ship's warp drive was off-line. In desperate need of her scientific expertise, Archer appointed T'Pol as his second-in-command. He made it perfectly clear to her, however, that he bitterly resented her betraying him to Forrest, and that he would order her execution were it not for the fact that no other officer was qualified to replace her while the Defiant was only partially operational. Archer contemptuously dismissed T'Pol's argument that it was her duty to stop him, since his orders to relieve Captain Forrest were fraudulent. He icily told her that he felt the Vulcans were responsible for the rebellion against the Terran Empire, and gave her dire warnings as to what would happen to her should she betray him a second time.
T'Pol studied the Defiant's historical database and learned of the United Federation of Planets that was eventually formed in its universe. She was intrigued by the fact that it was an alliance of several alien races, all of whom were regarded as equals. T'Pol became alarmed when Archer killed Admiral Black and announced his intention to return to Earth, overthrow the Emperor, and take the throne for himself. She feared that many Vulcans would be killed under his reign, as he blamed them for the rebellion. She enlisted the help of Soval, a Vulcan crewman on board the Avenger, and downloaded the Defiant's tactical information to him before Archer had her and all other alien crewmembers transferred off the Defiant to the Avenger. Both T'Pol and Soval convinced Phlox to sabotage the Defiant so that the Avenger could destroy it.
Before this was done, however, communications officer Hoshi Sato discovered the information T'Pol downloaded from the Defiant and arrested T'Pol on the Avenger, after fierce hand-to-hand combat. T'Pol was interrogated by Archer and Sato, but despite their best efforts, they failed to get any information out of her. T'Pol defiantly warned Archer that although it may take centuries, Humanity would ultimately pay for its arrogance. Sato, who hated T'Pol, was adamant that Archer execute her for her treachery immediately.