Silver Dalek

Silver Daleks were Dalek drones who were distinguished by their gun-metal blue and silver casings. (PROSE: Mission to the Unknown) They were among the slatted casings which succeeded the Dalek War Machine as the most common variant of the Dalek travel machine sometime between the Daleks' encounter with Lodian, Yvric and Zet (COMIC: Legacy of Yesteryear) and the One in a Million Dalek's rebellion. (COMIC: Shadow of Humanity)

Hierarchy
The silver Daleks were subordinate to black Supreme Daleks, black and silver Dalek saucer commanders, (TV: The Dalek Invasion of Earth) and the Dalek Emperor, who was himself in a massive silver casing. In addition, the Emperor was protected by the Emperor's Personal Guard; mostly silver, they were distinguished by their black domes, a distinction which was later adapted to the bronze Daleks. (TV: The Evil of the Daleks, The Parting of the Ways)

Origins
Silver Daleks' armours were among the slatted casings which succeeded the Dalek War Machine as the most common variant of the Dalek travel machine, sometime between the Daleks' encounter with Lodian, Yvric and Zet (COMIC: Legacy of Yesteryear) and the One in a Million Dalek's rebellion. (COMIC: Shadow of Humanity)

Conquests
Following the conquest of Earth in the 22nd century, silver Daleks occupied the planet, led by the Black Dalek known as the Supreme Controller while each saucer was under the command of a Dalek saucer commander. They used Robomen for patrols and overseeing slaves. The Sixth Doctor foiled their plan to unleash a Varga plant virus and new Robomen Elite in 2163 and erased any record of his involvement afterwards but the invasion continued. (AUDIO: Masters of Earth) The Daleks commenced a mining operation in Bedfordshire in order to reach the Earth's magnetic core, replace it with a propulsion system, and turn the whole planet into a massive spacecraft. Some time after their takeover of Earth, however, the First Doctor foiled the plan before its completion; the pit they had dug turned into an active volcano, the eruption of which killed the remaining Daleks and destroyed their base. (TV: The Dalek Invasion of Earth)

Using a taranium-powered Dalek time machines of their own, an execution squad of silver Daleks pursued the TARDIS throughout history in order kill the First Doctor and his companions, ultimately leading them into conflict with the Mechonoids in their Mechonoid City. The Dalek Leader slipped away from the battle with the Mechonoids after it realised that the assassination squad had no chance of winning. As the last surviving Dalek and in an act of self-sacrifice, it hacked into the city's computer systems and set the whole place to self-destruct, hoping to kill the Doctor and his companions in the blast. The Doctor escaped and the squad failed in their mission. (TV: The Chase, PROSE: The Chase)

In the year 4000, the silver Daleks formed an alliance with the Outer Galaxies and Mavic Chen, who supplied them with an emm of Taranium, which was vital to the Time Destructor to wipe out the Solar System. However, the First Doctor escaped with the Taranium, and the Daleks pursued him until he apparently surrendered it to them - this turned out to be a fake, however, so a Dalek task force with a Red Dalek sent from Skaro in another time machine by the Dalek Prime pursued him and his companions through time until the core was finally recovered in Ancient Egypt. They successfully recovered the core, although the Red Dalek was killed by rocks during the battle with the Egyptians. The Doctor activated the Time Destructor which destroyed the Daleks, their invasion fleet and left Kembel a wasteland. (TV: Mission to the Unknown, The Daleks' Master Plan, PROSE: The Mutation of Time)

A Dalek factory ship crashed on Vulcan, where it lay for three hundred years until a human scientist named Lesterson recovered and penetrated the capsule. Once activated, the surviving silver Daleks in the capsule decided to pose as obedient robotic servant drones, claiming to be the colonists' willing servants. The Daleks took advantage of the colonists' naive trust to establish a reproduction plant - on a conveyor belt system - with which to increase their numbers. The Second Doctor eventually destroyed the Daleks by turning the colony's power source against them, but not before the Daleks killed a vast number of the colony's inhabitants. (TV: The Power of the Daleks)

The Dalek Civil War
Under the leadership of the Dalek Emperor, silver Daleks were summoned to 19th century Earth by the human businessman and amateur alchemist Theodore Maxtible, who had devised a new form of time travel involving mirrors and static electricity, they took over Maxtible's techniques for themselves. Armed with this venue for time-space travel, they used it to trick the Second Doctor into a trap. They asked him to implant the Human Factor into three Daleks, claiming that they desired to become humanised Daleks allying the best of mankind and Dalek-kind. In truth, the Emperor's design was that the Doctor's experiment would, by contrast, also identify the Dalek Factor, which they would then spread through Earth's history. However, having realised the Daleks' plan, the Doctor encouraged the three humanised Daleks, Alpha, Beta and Omega, to defend themselves. Fearful of the implications, the Emperor ordered many Daleks through an archway that would re-implant the Dalek Factor. However, the Doctor switched factors so that all Daleks through the archway were humanised. A conflict between the normal and humanised Daleks inevitably broke out across Skaro, apparently ending the Daleks. (TV: The Evil of the Daleks)

After the Dalek war, a ship of silver Daleks travelled to the planet Exxilon in search of Parrinium, where all of its power was taken by the Exxilon City. The Dalek task-force encountered the Third Doctor and his companion Sarah Jane Smith along with a human expedition. They attempted to gun down the humans, but discovered that the Exxilon City had also drained their power supplies, rendering their gunsticks useless and forcing the Daleks to form an unholy alliance with the humans. While their gunsticks did not work, the Daleks replaced them with machine guns and enslaved the Exxillons in search for parrinium. When their power was restored, the Daleks revealed they were the cause of the Space plague and were about to fire plague missiles to kill the Exxilons and the Doctor as they made their getaway in their ship. However, it and its crew were destroyed by Dan Galloway, who had stowed away on the ship with a Dalek bomb, which he detonated. (TV:  Death to the Daleks)

Phasing out
At later points in the Daleks' history, Silver Daleks were phased out and Grey Daleks became the normal form of Dalek drone. (TV: Frontier in Space, Destiny of the Daleks, Revelation of the Daleks, etc.) Grey Daleks had, according one account of the Daleks' origin, been the original form of Mark III Travel Machine presented by Davros to the Kaled elite. (TV: Genesis of the Daleks)

Persistence of Silver Daleks
However, some Silver Daleks were left in the universe.

For example, many survived encounters with the Doctor; classed as insane, they were taken to the Dalek Asylum. The insane Daleks died when the asylum was destroyed by the Parliament of the Daleks. (TV: Asylum of the Daleks)

Silver Daleks were also among a diverse range of Daleks who, led by a red Supreme Dalek, resided on the rebuilt Skaro where Davros lived. (TV: The Magician's Apprentice) One bronze Dalek was killed by, allowing Clara Oswald to temporarily operate its casing so that they could safely navigate the Dalek City. When the Doctor's regeneration energy rejuvenated the discarded Daleks from the sewers, the city-dwelling Daleks were overrun and destroyed. (TV: The Witch's Familiar)

Other references
During his trial, the Second Doctor recalled the Daleks, specifically drawing the image of a familiar silver Dalek in the Thought Channel, as one of the adversaries he had broken the Time Lord code of non-interference to fight. (TV: The War Games)

Behind the scenes

 * Silver Daleks serve as foot soldiers in the theatrical film Daleks' Invasion Earth 2150 A.D., adapted from The Dalek Invasion of Earth.