Ascendant Justice was a Covenant CAS-class assault carrier, one of the seven ships sent to Installation 04 shortly after its destruction. It was presumably part of the Second Fleet of Homogeneous Clarity and was captured by SPARTAN John-117 and the other human survivors of the Battle of Installation 04.
The Ascendant Justice had seven plasma turrets and was noted to have three thousand Covenant personnel, mostly composed of Huragok, along with an unusually small crew of combat personnel: a light company of Unggoy and only a hundred Sangheili. There were apparently enough Huragok on board to merit them having an access tunnel of their own. John-117 noted that he "...hadn't seen anything like this on the Truth and Reconciliation," and that it was "armed like a ship of war... yet had the support staff of a refit vessel." It possessed a crude Covenant Associated Intelligence construct and software for replicating AI matrices.
The ship was present at the destruction of Installation 04, searching the wreckage for transmissions from survivors. It was soon boarded and captured by a small team of UNSC survivors, which included John-117, Staff Sergeant Avery Johnson, Lieutenant Elias Haverson, Corporal Locklear, Warrant Officer Sheila Polaski, and Cortana. The survivors then used Ascendant Justice to return to Reach and evacuate a small number of SPARTAN survivors, Vice Admiral Danforth Whitcomb and Dr. Catherine Halsey, as well as a Forerunner artifact from the planet, attaching to the wreckage of the frigate UNSC Gettysburg via external hard points for additional power. They then escaped through Slipspace toward the Eridanus Secundus system, becoming the first ship to ever go into Slipspace so close to a planet. En route to Eridanus Secondus, Ascendant Justice was forced to engage multiple Covenant warships, including several cruisers and carriers, in an alternate Slipspace. Furthermore, some surviving Sangheili crew members had sabotaged Ascendant Justice's main power conduit, forcing the SPARTANs to go on an extravehicular mission and weld the breach. This mission resulted in the deaths of the entire surviving Sangheili crew, but also killed Warrant Officer Polaski, and SPARTANs Anton-044 and Li-008.
The ship received assistance from remaining rebels in a small asteroid colony at Eridanus Secundus, who provided personnel and repairs for the ship's weaponry, before being discovered by the Covenant. Though Ascendant Justice engaged the initial Covenant forces in ship-to-ship combat, reinforcements arrived en masse, forcing it to abandon the colony to the Covenant.
After fleeing from Eridanus Secondus, the crew of Ascendant Justice discovered the Unyielding Hierophant, a Covenant refit-and-repair station, which was being used to service a Covenant invasion force that was poised to invade Earth. Vice Admiral Whitcomb then initiated Operation: FIRST STRIKE, in which the UNSC-commandeered Ascendant Justice deployed the remaining SPARTANs near the Unyielding Hierophant in a heavily modified Spirit dropship, and started a self-destruct sequence in one of the station's reactor rooms. The SPARTANs managed to escape from the station and travel to the far side of a nearby moon where the Gettysburg was waiting for them. Vice Admiral Whitcomb and Lieutenant Haverson had detached the Ascendant Justice from the Gettysburg and taken it in a slingshot orbit around the moon. Vice Admiral Whitcomb pretended to have the Forerunner crystal by using a hologram and challenged the Covenant to come and claim it. The Covenant did not want to fire on Ascendant Justice because the crystal was supposedly on it. The two used the momentum from their slingshot orbit to crash into the station even after the Covenant had cut the ship's engines off with laser fire. Whitcomb then ordered John-117 to see what was left of the Covenant and then "...hightail the intel back to Earth." The last few seconds of visual and audio record from Ascendant Justice showed the door crashing to the ground and the Admiral opening fire with an SMG. The reactors on the Unyielding Hierophant then overloaded and exploded, destroying Ascendant Justice and over four hundred enemy vessels. Only a few Covenant ships survived the catastrophe, which delayed the Prophet of Truth's plan to invade Earth. Both Vice Admiral Whitcomb and Lieutenant Haverson were killed.
Ascendant Justice's Slipspace drive allowed the Gettysburg to reach Earth and warn the UNSC leadership of the Covenant's plans to invade Earth. Ascendant Justice itself came to a climatic end as it was used to draw in the majority of the covenant invasion fleet toward the imminently detonating Unyielding Hierophant battlestation.
Only four members of Ascendant Justice's original Covenant crew survived its capture. A Special Operations Sangheili who engaged the Master Chief in hand-to-hand combat was shot and pushed into an escape pod, and a few Huragok that were taken to Earth on the Gettysburg which were turned over to the Office of Naval Intelligence.
- Fans originally believed this vessel to be the flagship of the Fleet of Particular Justice, though this idea was contradicted by the Halo Graphic Novel story The Last Voyage of the Infinite Succor. The ship was presumably part of the Second Fleet of Homogenous Clarity, which protected High Charity.
- While aboard, Cortana successfully completed the first known in-atmosphere slipspace jump, usually impossible due to the inter-lapping gravitation fields. This information was later leaked to the Covenant fleet around Reach by the ship's AI. In-atmosphere Slipspace jumps were subsequently performed by Covenant forces during the Battle of Earth.
- Ascendant Justice can briefly be seen in the secret Threshold terminal in Halo: Combat Evolved Anniversary.
- The Ascendant Justice is clearly a carrier (as seen in the Anniversary terminal), but is too large to be a DDS-class and too small to be a CSO-class supercarrier