Mantle's Approach

Mantle's Approach was the Didact's personal flagship.

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 the Master Builder Faber. 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 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 due to the Librarian's intervention. 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 and defeat the Didact with a pulse grenade.

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, taking the Mantle's Approach along with it. 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 at the cost of her own. The remains of Mantle's Approach formed a debris field over Earth. However, pieces of the ship's remains entered the slipspace rupture nearby and 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.

Trivia
Mantle's Approach resembles a Reaper (particularly of the Sovereign class) from the Mass Effect universe. Keith Szarabajka, the Ur-Didact's voice actor, previously voiced the Reaper Harbinger, who shares similar goals to the Didact. Namely, Harbinger seeks to convert all sufficiently advanced sentient life (particularly humanity) into mechanical form, creating a new Reaper, and views this act not as genocide but as a sort of cosmic necessity.
 * Catalog mentions that a section of Mantle's Approach conducted an emergency slipspace jump when the HAVOK detonated

List of appearances

 * Halo 4
 * Terminals
 * Halo: Silentium
 * Halo: Escalation