The Master used this ship as his base after he took over the world. He kept the Doctor prisoner here and used it to store the TARDIS. However, the ship was critically damaged when the TARDIS (now a paradox machine) was destroyed by his companions. However, this reversed time, meaning that both the TARDIS and the Valiant were repaired.
The Valiant was also used when the Daleks invaded Earth (again) under the regime of Dalek $wag, Davros, and Dalek Caan. Although the ship managed to cripple and destroy many Dalek flying Saucers, thousands broke through the Human defences and laid waste to the planet. The Valiant was hovering over New York when the city was bombarded from above, and as the city fell the Valiant attempted to retreat. However, the ship was overrun by Daleks who got inside and attacked the engines. Taking down several Daleks and a flying saucer, as well as the Daleks on board, the Valiant crashed into the sea and then exploded, taking a large chunk of Manhatten with it.