In the mirror universe, the free starship Valiant was a Memory Omega jaunt ship in service to the Terran Rebellion, and subsequently the Galactic Commonwealth, in the late 24th century. The Valiant was part of the fleet built by Memory Omega to overthrow the Klingon-Cardassian Alliance. (ST - Mirror Universe novel: Rise Like Lions)
The Valiant was part of the fleet of jaunt ships - battleships with an in-built wormhole generator - Memory Omega built at Erebus Station, beyond the rim of the Milky Way Galaxy. These ships were given to Terran Rebellion personnel after they had received training on the station.
In the year 2378, the Valiant jaunted to the orbit of Bajor after the planet had been saved from destruction from a Klingon trilithium warhead by a jaunt ship fleet led by Captain Jean-Luc Picard. The Valiant delivered Memory Omega Director Saavik to the Elemspur Monastery to meet with the leaders of the Terran Rebellion. Saavik announced that with the cease-fire with the Klingon Empire in effect, the final stage of the revolution was at hand - the war to defeat the Cardassians. (ST - Mirror Universe novel: Rise Like Lions)
In January 2379, the war was over and the fleet of jaunt ships re-launched with missions of defense and peaceful exploration. In July, Commonwealth Assembly settled on a name for their new, democratic nation, the Galactic Commonwealth. (ST - Mirror Universe novel: Rise Like Lions)