The Battle of GeoComTex began when the "last" Dalek, called the Metaltron by Henry van Statten, escaped from an area within a GeoComTex facility known as the Vault in 2012. Two hundred security personnel fought the Dalek. All were exterminated without damaging it as the Dalek was protected with a forcefield which melted the bullets fired at it, and it had the ability to rotate its midsection so it was able to shoot multiple targets without completely turning itself around.
The Dalek continued travelling through the facility, up through the facility's staircases. In one skirmish with the facility's remaining security forces, it activated the fire extinguishers, soaking the personnel with water before the Dalek opened fire, electrocuting all the humans simultaneously with its weapons' conductivity. Over 200 died in the battle.
The Dalek finally located van Statten, who had held it captive, and nearly killed him, but was halted by Rose Tyler. Rose had some sway over the Dalek's actions as it had absorbed her DNA to regenerate itself and escape its captivity. A side effect of this absorption was an awakening of its emotions. Though the Ninth Doctor threatened to destroy the Dalek with an alien weapon, he was also stopped by Rose, who showed him the Dalek's change.
The Dalek ended its emotion-induced pain by self-destructing. It asked Rose to give this order herself, which she did reluctantly. Following this outcome the facility was sealed off, and van Statten's memory was erased by orders of his assistant, Diana Goddard, in a hostile takeover. (TV: Dalek)