Sirius IV

Sirius IV was a planet colonised by humans.

In 2520, after being informed Draconia was at war with Earth, Lieutenant Ruji of the Draconian Secret Service was ordered to launch Neutronic missile at Sirius IV by General Chusa. Ruji refused. Chusa then revealed there was no war and that the order to attack Sirius IV was actually a loyalty test which Ruji had failed. (AUDIO: Conspiracy in Space)

By 2540, Sirius IV had been granted dominion status within the Earth Empire. As a dominion, Sirius IV had great autonomy within the Empire; it dealt with Earth mostly as an equal. The Master once used this special status as a way to negotiate for the release of the Third Doctor and Jo Grant into his custody. By fabricating charges against them on Sirius IV, he was able to successfully argue that he had greater claim to the prisoners than Earth Security. General Williams took a dismissive view of Sirius IV's dominion status. (TV: Frontier in Space) According to another account, the planet in question was Alderberan IV. (PROSE: Doctor Who and the Space War)

The Sixth Doctor once recalled visiting Sirius IV to Evelyn Smythe. (AUDIO: Pier Pressure)