Fall of Reach (Earth-5162)

"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 billions, and when Reach falls—and fall it will—there will be nothing left to stand between them - and Earth."

- - Dr. Catherine Halsey

Background
before July 19th, 2552, the Office of Naval Intelligence ran calculations where they predicted the movement of the Covenant through the human colonies. These calculations determinated that the Epsilon Eridani system had an 87% probability of being discovered by the Covenant in the span of five months. Admiral Margaret Parangosky, director of ONI, argued with Vice Admiral Hieronymus Michael Stanforth about using Reach as an scapegoat for the classified Operation RED FLAG, considering that the recently-discovered presence of forerunner artifacts on the planet would draw the Covenant's attention to the planet. The rest of the UNSC and the population of the planet, however, were completely unaware of this information.

The prediction came true in less than a month; after the Covenant suffered a rare defeat at the Battle of Sigma Octanus IV, the Covenant tracked the UNSC Iroquois to further advance in UNSC-held space. Once the Iroquois returned to Reach, the human presence on the planet was known to the Covenant.