Planet 14

Planet 14, also known as Sol XIV or Planet Sigma Gamma 14, (PROSE: The Invasion) was, according to one account, the fourteenth planet from Sol, inhabited by Cybermen. (PROSE: Iceberg) Following the destruction of Mondas, Planet 14 was used as a base by the Cybermen during numerous attempted invasions of Earth. (PROSE: Killing Ground)

Whilst Mondas was drifting through space, the Cyberman of the Faction emigrated to Planet 14, where they evolved separately from the CyberMondans who remained on the homeworld. Whilst on Planet 14 they pursued their goal of total Cyber-conversion, (PROSE: Iceberg) but were later driven away when the planet's own power was used against them, resulting in a catastrophic explosion. (PROSE: Scientific Adviser)

Another account stated that Planet 14 was the Cybermen's home planet of Mondas earlier in its history, back when it was also known as Marinus. Using a worldshaper, the Voord of Marinus quick-evolved themselves into the earliest Cybermen before the Sixth Doctor and Jamie McCrimmon encountered them, Jamie destroying the worldshaper and causing a time field to change the planet into Mondas. (COMIC: The World Shapers)

During the attempted invasion of Earth involving International Electromatics, the Cyber-Planner told Tobias Vaughn that both the Second Doctor and Jamie had been on Planet 14. (TV: The Invasion)

Facing the Cybermen on a Mondasian colony ship, the Twelfth Doctor recalled Planet 14 as one of the worlds where they rose, and that he defeated them there. (TV: The Doctor Falls)

The Seventh Doctor kept a "To Do List" in his notebook, with no. 26 being "Return to Planet 14 to check up on provisional government". (PROSE: The Hollow Men)