Cyber-invasion (Earthshock)

In 2526, the Neomorph Cybermen prepared a Cyber-Army to invade the planet Earth. (TV: Earthshock, AUDIO: The Ultimate Cybermen)

Origin
In the 26th century, a new subspecies of Cyberman was proliferating throughout the galaxy of Mutter's Spiral. This subspecies would be identified by ArcHivist Hegelia as CyberNeomorph, which she believed to have been created through a combination of Cyber-technology after a group of surviving CyberNomads found the planet Telos and awoke the CyberTelosians in their tombs. (PROSE: Killing Ground, AUDIO: The Ultimate Cybermen)

Invasion
In the year 2526, several planets would unite in war against the Cybermen in an event called the Cyber-Wars. A force of Cybermen tried to devastate Earth using a Cyber-bomb and convert the survivors. Failing this, they hoped to crash the freighter into Earth and cause an ecological disaster. Although the attempt failed, the freighter was catapulted back in time to become the "meteor" that wiped out the dinosaurs. (TV: Earthshock)

Aftermath
Following the destruction of Briggs' freighter, the Fifth Doctor used the TARDIS to return the surviving human crew to their own time. Nyssa reported that the Cyber-Fleet had dispersed. (TV: Time-Flight)

Whilst its body was destroyed, the Cyber-Leader's core processing was downloaded to another unit. It attempted to recover a partially-converted Marc for use in espionage but was thwarted once again by the Fifth Doctor, whom it called a hypocrite for resorting to violence. Reprogrammed medical nano-drones invaded the Cyber-Leader's body, breaking down its conditioning and causing it to remember its past life, driving it mad. (AUDIO: Conversion)

What happened to the fleet afterwards remained a mystery to the CyberHive, an attempt at chronicling the history of the Cybermen from the Cyber-Documents. ArcHivist Hegelia suggested that an agreement was reached to join forces against the Cybermen, resulting in a Cyber-War beginning in the solar system with a battle between the main Cyber-Fleet and human forces which extended to other parts of the galaxy before the Cybermen were ultimately overcome. From the document Departure from Telos, Hegelia found an account of the Cybermen's attempt to leave Telos, which the ArcHivist believed was in anticipation of a significant attack on the planet by galactic forces. (AUDIO: The Ultimate Cybermen) This attempt ended in failure as Telos' Cyber-Control was destroyed along with seemingly all Cybermen on the planet. (TV: Attack of the Cybermen, AUDIO: The Ultimate Cybermen)

Behind the scenes

 * The Discontinuity Guide claims that the Cybermen who waged this attack were infact time travellers hailing from no earlier than the late 27th century, when the Cybermen failed to destroy Voga. Having failed to prevent the destruction of Mondas and destroy Earth in 1986, 15,000 Cybermen were sent back in an abortive attempt to change the outcome of the Cyber-Wars. It is speculated that this was the "last ditch plan" of the Cyber-race.