Armour was worn by many species for protection.
As the Ninth Doctor explained, Dalek mutants resided within their casings, which served as battle armour. (TV: Dalek) According to the Seventh Doctor, this armour was composed of bonded-polycarbide. (TV: Remembrance of the Daleks) As the Third Doctor noted, the Daleks' armour acted as a shield. (TV: Planet of the Daleks)
As Yvonne Hartman observed, the Cybermen of Pete's World converted humans by removing their brains and placing them in a suit of armour, (TV: Doomsday) which was known as a Cyber-suit. (AUDIO: Real Time, TV: The Age of Steel) Mercy Hartigan referred to these Cybermen as her "knights in shining armour, quite literally." (TV: The Next Doctor)
Aboard a Mondasian colony ship, the Mondasian colonists initially lacked guns that could shoot through the armour of the advanced Cybermen. However, Nardole was able to modify the Mondasian's rifles to provide a defense. (TV: The Doctor Falls)
By Ice WarriorsEdit
As explained by the Eleventh and Twelfth Doctors, the Ice Warriors constructed and wore bio-mechanical survival armour for protection so they could exist in the freezing cold of their homeworld, Mars. The former characterised them as becoming bio-mechanoid cyborgs, while the latter observed "the creature within is at one with its carapace." (TV: Cold War, Empress of Mars)