Operation: FIRST STRIKE

This operation was one of the most effective raids in UNSC history. In a desperate attempt to try and stop a massive Covenant force heading for Earth, 5 Spartans and a Vice-Admiral attacked the massing fleet with a single dropship and a captured Covenant Flagship, successfully annihilating the fleet and the station, Unyielding Hierophant.

The battle was integral as the Covenant did not know the strategic importance of their intended target, and thus their actual first attack on Earth was a much smaller 15 ship ill-fated fleet. This also was the first field detonation of the NOVA Bomb.

Raid of Reach and Earth
During the Raid of Reach and the subsequent battle within the Slipspace anomaly, the UNSC survivors found themselves well outside UNSC space with a damaged ship, the Gettysburg-Ascendant Justice. Further, communications intercepted between Covenant forces indicated plans to proceed to Earth after rendezvousing at their staging point around the Unyielding Hierophant.

The plan
Through luck, their location put them in a position where a small deviation from a direct course to Earth would take them near the Unyielding Hierophant, where they could launch a First Strike to dismantle the operations. The Marines and Spartans, once they discovered this, presented a plan to Vice Admiral Whitcomb whereby they would leave the Gettysburg-Ascendant Justice on a captured Covenant dropship in the middle of the slipspace jump and come out of slipspace near the staging area.

However, because of the volatile nature of slipspace, their trip trying to exit slipspace would throw them through extensive G-Forces. This meant that only the Spartans could be involved - all other humans would not be able to survive the transition. Additionally, the dropship would need to be reinforced so it could maintain structural integrity.

Infiltration Specialist
However, one hitch remained for the mission: getting into the Covenant network. To be able to complete the mission, the team would need to be able to get into the Covenant network to discover the weak points of whatever they were attacking. The nature of the mission implied that it would be a one-way trip. As such, Cortana was considered out of the question because she possessed to much vital information on the Halo rings and the Flood. Lieutenant Haverson suggested himself for the assignment, but this was shot down due to the fact that he would not survive long enough to get to the base.

It was at this point, however, that Cortana revealed that she had captured some Covenant code that could duplicate her system. Using this, she created a copy of her infiltration protocols, the copying routine, and her translation protocols. With this duplicate now available to them, they had a way to proceed with the mission

Aftermath
The survivors of the UNSC would proceed to Earth with their intelligence information still in-tact.

Despite the annihilation of the Covenant Armada, the first strike against Earth went ahead around when it was supposed to, though with a severely reduced force. It would later be discovered that despite the large size of the fleet being amassed, the Covenant forces were not aware of humanity's presence. All of the UNSC survivors would be present for the First Battle of Earth.

Timeline

 * O510 Hours: SPARTAN-117 officially presents the plan to the crew of the Gettysburg-Ascendant Justice. After much hesitation, 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 SPARTAN-117, SPARTAN-104, SPARTAN-058, SPARTAN-093, and SPARTAN-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. First encounter of Brutes in combat situation.
 * 1555 Hours: SPARTAN-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 Justice heads into the Covenant fleet, hoping to draw more Covenant vessels close to the station as it is detonating. Aboard are Admiral Whitcomb and Lieutenant Haverson.
 * 1620 Hours: The Spartan team uses Banshee fliers to escape the station.
 * 1625 Hours: The Unyielding Hierophant explodes, destroying 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, along with Sergeant 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.

UNSC

 * Vice Admiral Danforth Whitcomb
 * Lieutenant Haverson
 * Sergeant Johnson
 * Cortana
 * Spartan-117
 * Spartan-104
 * Spartan-058
 * Spartan-093
 * Spartan-043