The Assault on the Control Room was an engagement within the Battle of Installation 04.
After discovering the location of Installation 04's Control Room during the Battle of the Silent Cartographer, John-117 and Cortana traveled in Pelican dropship Echo 419 to a canyon via a maze of underground tunnels. The two quickly encountered heavy resistance from Covenant forces and realized that the Covenant had secured the area around the Control Room. After making their way to a bridge, they witnessed a Pelican containing Fire Team Zulu fly past, pursued by a Banshee. The Pelican dropped off most of the fire team and a Warthog before attempting to fly the rest into an adjacent canyon to reinforce another Marine fire team. However the dropship crashed after being hit by enemy fire, killing all aboard. Realizing that remnants of a Marine force that had been deployed around the Control Room were still present, John-117 and Cortana decided to provide support. Reaching the survivors of Fire Team Zulu, John-117 helped them destroy a Wraith, two Shades, and Covenant infantry.
Further down the canyon he encountered the second fire team, along with the crashed Pelican and a Scorpion Tank. Advancing, the human forces engaged a Covenant armored force and then several fortified positions. Although most of the Marine squads and fire teams around the Control Room had been wiped out, John-117 discovered another squad. Reinforced, the Spartan and Marines attacked another Covenant position, eliminating the defenders and clearing a LZ. With evac finally available, the surviving Marines held their position. SPARTAN-117 and Cortana continued alone.
After engaging more Covenant forces, he reached the Control Room. Upon his entrance, he placed Cortana into the Control room's mainframe. He was then ordered by Cortana to stop Keyes from reaching a Flood containment facility, which Keyes believed to be a weapons caché. He quickly heads back for Echo 419, leaving Cortana in the mainframe.