Battle of Canary Wharf

The Battle of Canary Wharf was one of the most major battles between Humans and aliens in history.

Background
The Battle of Canary Wharf had its roots in the escape of the Cult of Skaro and the Genesis Ark into the Void from the Last Great Time War. This caused a crack in the universe, allowing travel from one dimension to the next easier than it should be with the demise of the Time Lords. (DW: Doomsday)

Beginnings


From the crack in the universe, the Parallel Earth Cybermen were able to travel from their dimension into ours, and infiltrated the planet in the disguise as benign ghosts. (DW: Army of Ghosts)

After two months (three years in Parallel Earth time), the Cybermen suddenly appeareed in their true form in July 2007, breaking into houses and promising to upgrade all Humans, commanded by the new Cyber-Leader. (DW: Army of Ghosts/Doomsday, TW: Everything Changes)

Simaltaneously, the Cult of Skaro had exited the Void Ship with the Genesis Ark. The Cult, led by Dalek Sec, extracted information from a member of staff from Torchwood 1, and proceeded to communicate with the Cybermen via Dalek Thay and declare war (or in Dalek Sec's words, "pest control").

The battle
After a quick three-way fight (Humans versus Cybermen versus Daleks), the Cult travelled to the main room in Torchwood Tower (Canary Wharf), elevated outside above the roof, and opened the Genesis Ark, releasing millions of Daleks who, under Sec's command, proceeded to "exterminate all life-forms below", killing Human and Cyberman alike. (DW: Doomsday)

During the battle, the Cybermen began to convert Torchwood personnel, like Yvonne Hartman and Lisa Hallett in large numbers. (DW: Doomsday, TW: Cyberwoman) These were, at least in some cases, not full conversions, with the brain removed and put in a Cyber-shell, but partial conversions where the Cybermen built over the Human body beneath. (TW: Cyberwoman)

The Doctor and Rose Tyler opened the Void, sucking all the Daleks and Cybermen who had been in the Void back into it, and finally sucking Rose herself into the Parallel Earth where her parents (Pete Tyler and Jackie Tyler), and her boyfriend (Mickey Smith) were. The entire battle had lasted less than a day. (DW: Doomsday)

Aftermath
Afterwards, of Torchwood 1's 823, had only 27 known survivors, the rest being missing (many of them presumbably Cyber-converted and perhaps sucked into the Void, though this did not happen to Lisa Hallett and perhaps others) and 467 dead. (torchwood.org.uk) The governments of the Earth denied it ever happened and blamed it on mass hallucination caused by terrorists polluting the water supply with psychotropic drugs. (TW: Everything Changes)