Operation: FIRST STRIKE

"We're going to take this fight to the Covenant. We're going to launch a first strike."

- John-117

Operation: FIRST STRIKE was a raid by the survivors of the Battle of Installation 04 on the Covenant space station Unyielding Hierophant. It was the largest UNSC victory after the Battle of Sigma Octanus IV, and the most decisive since Admiral Cole's last stand at the Battle of Psi Serpentis.

Background
Having discovered the location of Earth, the Covenant were building up a massive invasion fleet of over five hundred ships strong to assault their target. This fleet was assembled by the Prophet of Truth in secrecy from the rest of the Hierarchs and the Covenant, and was commanded exclusively by the Jiralhanae instead of the Sangheili.

After discovering the plan from a piggyback transmission, Cortana and John-117 formulated a counter-plan that would result in either a massive victory or the deaths of the remaining active SPARTAN-IIs.

The Raid
In a desperate attempt to stop a massive Covenant armada heading for Earth, five Spartans infiltrated the Covenant battle station Unyielding Hierophant on-board a captured Spirit dropship. This was one of the first Spartan encounters with the Brutes, who guarded a temple in an atrium-like structure in the battle station. One of the Spartan-IIs, Grace-093, was killed by a Brute Shot through COM triangulation tactics. John-117 then rigged Grace's suit to execute a fail-safe fusion reactor overload, killing all Covenant in a ten-meter radius (among which were a dozen Grunts and four Elites). The Spartans fought their way to a reactor room and set the generators to overload. Once the reactors were set to overload, the Spartans returned to the atrium, opened the airlocks, and blew out a heavily enforced window that enclosed the atrium with hijacked Banshees, sucking all Covenant forces inside the atrium out to space. One of Cortana's clones was taken along and had to open the airlocks for the Spartans. Her copy of a copy in the Covenant network was discovered and forced to make hundreds of copies to protect herself. She successfully opened the airlocks and tied up the Covenant's communication by repeating error messages on their COM systems endlessly. The Spartans then traveled to the far side of a nearby moon and unexpectedly met the UNSC Gettysburg, now separated from the Ascendant Justice. Vice Admiral Danforth Whitcomb and Lieutenant Elias Haverson took the Ascendant Justice and crashed straight into the Unyielding Hierophant. Using a hologram, Whitcomb pretended to have the Forerunner Crystal on board the ship and challenged all Covenant forces in the system to try and take it from him. The Covenant battleships all gathered around the Ascendant Justice and the overloading battle station, attempting to take the Crystal from Whitcomb. The battle station then overloaded and exploded, killing the Vice Admiral and Lieutenant, destroying most of the Covenant fleet, and saving Earth from an unexpected attack.

The outcome and historical result of the battle was noteworthy as the Covenant did not yet know the strategic importance of their intended target, Earth. Thus, their actual first entrance into the Sol System was with a much smaller force than the ill-fated Epsilon Eridani System. This was crucial to the survival of the human home world and the significant UNSC presence on Earth.

Aftermath
After using a spy drone to view what was left of the fleet, the Gettysburg made a random jump away from the battlefield and then finally to Earth using the Ascendant Justice's Slipspace drive. There, the crew was finally able to warn Earth of the impending attack which was weaker than it would've been had this operation never taken place.

Timeline

 * 0510 Hours: Master Chief officially presents the plan to the crew of the Gettysburg-Ascendant Justice. After much hesitation, Vice Admiral Whitcomb approves.
 * 0530 Hours: The hybrid vessel passes through the Covenant armada in Slipspace. They are undetected, however a single Spirit launches from a hangar in the vessel. The dropship contains the SPARTAN-IIs: John-117, Fred-104, Linda-058, Grace-093, and Will-043. The dropship is undetected by the Covenant forces. The hybrid ship hides behind a nearby moon.
 * 0610 Hours: The dropship docks aboard the Unyielding Hierophant. The Spartans make their way through access pipes and conduits.
 * 1551 Hours: The Spartan team enters a temple inside the station. They are ambushed by a group of Brutes. One of the first encounter of Brutes since the battle of Harvest in combat situation.
 * 1555 Hours: Grace-093 is killed by a Brute Shot fired by the Brutes.
 * 1600 Hours: The Spartan team fights into the reactor room, where Cortana's copy initiates an overload of all 512 fusion reactors.
 * 1610 Hours: The Gettysburg and Ascendant Justice unlink. The Ascendant Justice heads into the Covenant fleet, hoping to draw more Covenant vessels close to the station as it is detonating. Aboard are Vice Admiral Whitcomb and Lieutenant Haverson.
 * 1620 Hours: The Spartan team uses Banshee fliers to escape the station.
 * 1625 Hours: The Unyielding Hierophant explodes, destroying approximately 488 of the 500 vessels in the area and heavily damaging the remainder.
 * 1630 Hours: The Gettysburg heads to Earth, carrying with it the only four Spartans actively in combat and confirmed alive, besides Gray Team and Maria-062, along with Staff Sergeant Avery J. Johnson and the surviving Covenant Engineers. The Gettysburg is outfitted with the Slipspace equipment from the Ascendant Justice, making it the fastest ship in the UNSC.