Cell 114

Cell 114 was the official designation for a species of which Jack Harkness was aware. Very little was known about them, since they did not usually leave survivors, though he did know that they carried out stealth alien invasions.

Methods and Technology
Cell 114 were ruthless killers. They tended to infiltrate planets, first with an advance guard of sleeper agents, sometimes watching for years, until they knew all they wanted to about the planet's dominant species and were ready to take over. Apparently, agents were modified to resemble the native species, with implants which could take information and transmit it to the main invasion fleet.

Active spying was not necessary; the implants constantly took in information from their surroundings. These implants even had built-in weaponry such as spikes and explosives. As well as visually resembling the natives, Cell agents could generate false sensor images as a personal force field less than a nanometre around their body (mainly the arm where the implant was stored) for protection. Their electromagnetic fields could disrupt nearby electrical devices such as light bulbs. Sleeper agents were given false memories and artificial personalities so that they believed themselves to be members of the infiltrated species. Their real memories stored in the implant until activation.

The Cell's main resource seemed to be the aforementioned implant located in the right arm (at least when mimicking humans), which contained collected data and transmitted it to the main invasion fleet. They also contained at least one small bomb with which an agent could carry out sabotage or a suicide bombing, or to self-destruct if capture was imminent. The arm could be transformed into a large spike for close combat. In the case of Beth Halloran, a threat to her life in the form of a burglar, caused her alien personality to awaken, take over and swiftly kill the intruders. (TV: Sleeper)

Cell 114 attacks tended to be both swift and devastating, requiring only a small number of agents to bring down a planet in most cases, due to the comprehensive intelligence gathered beforehand. Afterward, the planet would be stripped bare. This was described in gruesome detail to Hopkins' team by Iannamet. (WEB: torchwood.org.uk)

History
In 1998, Iannamet tracked a Cell 114 agent to Earth through the Cardiff Space-Time Rift and killed it. The agent had taken on a human disguise, indicating that there was already a Cell incursion on Earth with which it was attempting to make contact. Following this Cell incursion, Torchwood Three was alerted to Cell 114's existence. (WEB: torchwood.org.uk)

Cell 114 was in the process of infiltrating the Cardiff area on Earth until Torchwood Three became aware of their presence in 2008. Beth Halloran, who thought of herself as an ordinary human, made inexplicably fierce attacks on two burglars who had invaded her home. After Torchwood discovered the Cell presence, three other agents were activated and tried to set in motion a plan to explode nuclear missiles stored in an old mine near the city. Two of the Cell agents suicide-bombed a military oil pipeline and Cardiff's telecommunications station, and the remaining agent attempted to access the mine's nuclear missiles but was thwarted by Torchwood. However, the agent told the Torchwood team that there were more members of the Cell's invasion force already on Earth, before self-destructing. (TV: Sleeper)