Battle of Installation 00 (Earth-2042)

"Our fight is through the Portal, with the Confederacy and the bastard Truth!"

- Shipmaster Rtas 'Vadum

The Battle of Installation 00, also known as the Ark Conflict, was a large battle between the Galactic Republic-Fleet of Retribution alliance, the Confederacy of Independent Systems, the Flood, and Forerunner sentinel droids at the start of 19 BBY. It was one of the final battles of the Clone Wars, and was the major last stand of the Separatist military forces, making it one of the few major engagements in the entire war in which the Confederacy was on the defensive.

Source

 * https://www.halopedia.org/Battle_of_Installation_00