Fall of Reach (Earth-2915)

"We knew this day would come. They have found our fortress among the stars. The Covenant are on Reach. They will burn this planet, kill millions, and when Reach falls—and fall it will—there will be nothing left to stand between them - and Earth."

- Dr. Catherine Halsey

The Fall of Reach, also known as the Battle of Reach, was one of the largest and bloodiest engagements in the Human-Covenant War. It was fought on and around the human colony world of Reach in the Epsilon Eridani system, between the United Nations Space Command and the Union of Progressive Peoples  against the Covenant from July 25 to August 30, 2552.

Initial skirmishes began on July 23, 2552, when a small Covenant task force led by the supercarrier Long Night of Solace covertly established a foothold on Reach. The Covenant began to solidify their hold and began searching for forerunner relics as the UNSC and the UPP counter-attacked, attempting to drive the Covenant off the surface before reinforcements arrived. Ultimately, the UNSC was unsuccessful, and substantial Covenant reinforcements under Thel 'Vadamee arrived in the system. After hard fighting, the Covenant breached the orbital defense grid and overran the UNSC's planetside forces. After overwhelming the defenders, the Covenant glassed the planet. Isolated skirmishes between UNSC remnants and the Covenant forces continued until their recovery by a small rescue party led by John-117.

Source

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