The Doctor’s TARDIS — sometimes called the Ship by the First Doctor, and most often known simply as the TARDIS (Time And Relative Dimension In Space) — was the Doctor’s primary means of transport. It was capable of travelling through space and time. The Doctor voyaged in his vessel from the Big Bang to the end of the universe in the year 100 trillion.
The craft was prone to a number of technical faults, ranging from depleted resources to malfunctioning controls to a simple inability to arrive at the proper time or location.
However, because the TARDIS was a living being, these “faults” may have instead been at least partially attributed to the manifestation of the Ship’s free will; in other words, she could have actively intended to only appear unreliable. Indeed, the TARDIS herself once told the Eleventh Doctor that she deliberately refused to take him where he wanted to go, so as to take him where he needed to go.