Operation: ABOMINATION

"This is the Captain of the Edge of the World- a flood infestation has made it aboard the ship and have already infected our frigates. We're outnumbered, and we're attempting to take out the slipspace drive before they can jump back to-"

- Captain Miguel Hanashki of the UNSC Edge of the World.

Operation: ABOMINATION was a failed UNSC expansion into the Perseus Arm of the galaxy. Spearheaded by three ships, the UNSC Apparent Vagueness, the UNSC Ring of Life, and the UNSC Edge of the World, they would use reverse-engineered forerunner slipspace drives to defeat the Covenant splinter faction, the Gods of Orion, who by that point had built their own fleet of forerunner ships. While the space battle had led to a stalemate, the capital world of the Gods of Orion was initially taken by the UNSC successfully, up until the attack on the Covenant's last stronghold, a forerunner temple.

During the battle for control the temple- led by Spartan-III Jay-I425- the Covenant unleashed their secret weapon, a wave of flood infection forms and other monsters. However, this quickly turned against them, and the flood began infecting both the Gods of Orion and UNSC alike. Infecting almost every living thing on the planet, the flood quickly managed to build a gravemind in a matter of weeks, while the UNSC and GO ships were blissfully unaware of the infestation below. During the infestation, Jay and several other Spartan-IVs were infected by the parasite, and their knowledge was given to this new Gravemind.

A week later, a GO ship was infected after landing on the surface. Quickly going back into space, the entire GO fleet was infected. The end of the Operation: ABOMINATION resulted in every ship in the system being infected by the flood.