Space capsule (The Power of the Daleks)

A space capsule crewed by three silver Daleks crash landed in the mercury swamp of the planet Vulcan. (TV: The Power of the Daleks) According to the Time Lords' Dalek Combat Training Manual, this was a scout craft used for reconnaissance missions. (PROSE: Dalek Combat Training Manual)

History
In a transmission recovered and recorded in The Dalek Conquests, the capsule was on a course which entailed traversing the orbital path of the planet Vulcan when its engines were hit by a meteor strike, disabling maneuvering controls. As a result, the capsule was caught in Vulcan's gravitational pull. Though the Dalek crew attempted to transmit a distress signal to their home planet, Skaro, they found that their transmitter was non-functional as main power shut down, leading to a crash landing on Vulcan. (AUDIO: The Dalek Conquests)

Two hundred years later, a human colony had been established on the planet Vulcan. The Daleks were found in their space capsule underground and then reactivated by a scientist called Lesterson. This overlapped with the rebellion against Hensell led by Bragen. The rebellion failed after the Daleks began an indiscriminate slaughter of the colonists but the Second Doctor overloaded their temporary static circuit from the colony's electricity supply. (TV: The Power of the Daleks)

Behind the scenes
The Discontinuity Guide claimed that the ship was one of those which escaped the destruction caused by the Dalek Civil War on Skaro before crashing on Vulcan in the 21st or early 22nd century, preceding the 22nd century Dalek invasion of Earth. It is further noted that, since the Fourth Doctor inadvertently changed Dalek history so that Davros survived, this event would have occurred vastly differently if it happened at all in the new timeline.