Mantle's Approach

Mantle's Approach was an unordered command vessel built specifically to serve as the personal flagship of the Didact. The only vessel of its kind, the Mantle's Approach played a pivotal roles in the final years of the Forerunner-Flood war executing the Didact's will by launching an army of machine-warriors that were effectively impervious to the Flood, and later composing humans to create more of these warriors. The ship would remain on Requiem throughout the Didact's imprisonment, only to be awakened along with the Forerunner. The Mantle's Approach would ultimately be destroyed by John-117 and Cortana with a well-placed nuclear warhead. What remained of the ship's core escaped via an emergency slipspace jump to the shield world of Genesis.

Origins
This massive vessel was once captained by the Didact at the height of Forerunner power. Built during the human-Forerunner wars, it served as the Ur-Didact's personal command ship. The design seed of the vessel was not approved by the Ecumene Council, but by Master Builder Faber himself. While not the largest of Forerunner ships, Mantle's Approach was the fastest and most heavily armed warship in the Forerunner fleet. The ship held a number of escort craft for transport within the vessel, and at its height it possessed enormous support fleets of both manned and automated combat craft, including war sphinxes, sentinels and internally-stored fighters. During the Didact's assault on Omega Halo, it had an escort of thousands of sentinels. Like many Forerunner warships, Mantle's Approach possessed a cloaking ability.

Forerunner-Flood war
During the final years of the Forerunner-Flood war, after being returned to the ecumene from his captivity at the clutches of the Gravemind, the Ur-Didact re-assumed command of Mantle's Approach. He used the ship to travel to Nomdagro and later when he followed the Librarian's ship, Audacity, to the greater Ark. Once there, he remained aboard the Mantle's Approach in orbit over the Ark, where he was briefly visited by the Librarian. When the Ark fell under siege by Flood forces, the Didact moved the ship to the nearby Omega Halo and used a Composer, a device designed to transfer organic consciousness to digital form, integrated to the ship to harvest the essences of the human population that had been transplanted to the ring. He then immediately departed aboard Mantle's Approach, headed for Requiem, his primary shield world. He docked the ship inside Requiem and began to process the harvested human essences into the next generation of Promethean Knights.

However, the Librarian had trailed her husband on Audacity, aiming to put an end to his genocidal schemes. With the admission of the Didact's lieutenant, Endurance-of-Will, the Librarian entered Mantle's Approach and confronted the Didact in the command center. She incapacitated the Didact, placed him in a combat Cryptum previously stored on Mantle's Approach and sealed the Cryptum inside the core of Requiem. She also sealed the ship itself within Requiem.

Modern era
After his awakening in July 2557, the Didact quickly escaped in his Cryptum and, once the necessary preparations were complete, he recoupled the Cryptum with Mantle's Approach and took off immediately. He jumped to Ivanoff Station alongside a Covenant fleet, intent on reclaiming the Composer. The Didact test-fired the Composer on the station, then proceeded to Earth to settle his personal war with humanity once and for all. Although Earth had been warned of the attack, the planet's orbital defense platforms and the Home Fleet were unable to stop the colossal Forerunner ship.

Unbeknownst to the Ur-Didact, however, Spartan John-117 had survived the Composer's deadly pulse thanks to immunization provided by the Librarian. Pursuing Mantle's Approach aboard a nuclear-armed F-41 Broadsword, the Spartan took out the ship's point defense turrets, allowing the to punch a hole through the ship's hull with her fore weapons. The Master Chief then fought his way through the ship, eventually finding the Didact controlling the Composer under an impenetrable force field. The AI Cortana overloaded the shields by flooding the ship's mainframe with her rampant duplicates, allowing the Chief to confront the Didact. Although John was no match for the Didact's powerful abilities, Cortana was able to immobilize the Promethean with hard light shackles, allowing the Chief to plant a pulse grenade in the Didact's armour. The resulting explosion knocked the Didact off balance and sent him falling into a slipspace portal underneath the Composer.

With the Composer already firing upon New Phoenix, URNA, the Spartan manually detonated the HAVOK warhead as a desperate last resort. The Composer was destroyed by the HAVOK nuke, along with the majority of the Mantle's Approach. The dying Cortana teleported the Master Chief out of the ship at the very last moment and created a hard light barrier around him, saving John's life. The remains of Mantle's Approach formed a debris field over Earth. Pieces of the ship's remains exited over Installation 03 in the Khaphrae system. Some of the debris entered the atmosphere of the Halo installation—an event observed by SPARTAN-II Black Team.

During the HAVOK nuke's detonation, self-preservation protocols shunted the core seed of Mantle's Approach, including the remnants of Cortana's personality matrix, via emergency slipspace jump, to the nearest repair facility on record, Genesis. As a result, Cortana was able to access the Domain and cure her rampancy. Her comments when reuniting with John in October 2558 suggest that the ship's remains crashed on the planet.

Design details
The Mantle's Approach featured a core seed that acted as the heart of the ship. Even if the ship was destroyed, the core seed could rebuild it as long as it had access to raw materials of sufficient quality. The ship featured a specialized command sector known as the Hall of Command. The Heroes' Walk housed the barracks, training grounds, museums, and halls of honors for the ship's Forerunners. After the Warrior-Servants voluntarily composed themselves, the section was no longer necessary. The Exalted Sepulcher was remodeled to service composed Prometheans. The Mantle's Approach was capable of constructing a billion Knight shells, but there were never enough essences available to fill them. Large numbers of empty Knight shells in maintenance cradles survived the ship's destruction and its' remnants arrival at Genesis. The vessel possessed powerful shielding, able to shrug off attacks by the UNSC Home Fleet and orbital MAC platforms without any trouble. Only a shot from two of the 's main batteries managed to penetrate the shields and they failed to inflict any significant damage upon the vessel which was able to shift its structure to quickly close the hole. Even getting this shot required the Infinity to move into relatively close proximity and for the point-defense guns in that area to be destroyed.

Hull and weaponry
The Mantle's Approach featured a variable geometry hull full of programmable matter, hard light, and energy interlocks in order to change its shape for fighting the Flood and Ancient Humanity. The ship's main cannon was a heavy ion weapon system adapted from emplacements used on planet-cracking siege platforms. Firing a bolt of exotic matter accelerated to a significant fraction of the speed of light, the cannon was able to buckle continental plates and disintegrate phase-rotated fortifications. However, the ship must reconfigure after a single shot. Another important armament was the stasis tension driver, an array of three projectors that pairs quantum singularity generators with repurposed torsion drivers. Together, they generate localized space-time distortions that impede the formation of slipspace ruptures and jam all superluminal communications and sensors. The vessel's point-defense guns were potent, able to destroy several UNSC ships that were in close-proximity with relative ease.

List of appearances

 * Halo 4
 * Terminals
 * Halo: Silentium
 * Halo: Escalation
 * Halo 5: Guardians
 * Halo Mythos
 * Halo: Shadows of Reach