Magnetic Accelerator Cannon

"That MAC gun can put a round clean through a Covenant capital ship." —Sergeant Johnson, talking to Master Chief on board the Orbital Defense
Platform Cairo.

The Magnetic Accelerator Cannon, also known as Mass Accelerator Cannon or the MAC gun or MAC cannon, is a large coilgun that serves as the primary offensive weapon for UNSC warships.
A larger variant is in service aboard Orbital Defense Platforms. Within the UNSC arsenal, only nuclear ordnance exceeds the power of the MAC. The M68 Gauss Cannon used by UNSC ground forces mounted on some Warthogs may be regarded as a relative of the MAC, albeit on a much smaller scale.

Overview

Mounting
The size of a Magnetic Accelerator Cannon is such that it is normally an integral component of a warship's structure. Some types of Defense Stations are literally built around the massive weapon for orbital defense. A good example of this is Cairo Station. The MAC gun can be clearly seen protruding from the rest of the platform.

Ammunition
A MAC typically fires slugs of either ferric tungsten or depleted uranium slugs at 40% of the speed of light. The high muzzle speed gives the 600 ton slug the kinetic energy and momentum necessary to damage a target and partially mitigates the unguided nature of the slug and its lack of maneuverability.
The Super MAC Slug can be seen on the level Cairo Station; Go out of the elevator to the bomb and immediately turn left, then go into the hollow rail in the middle of the room, you will see the 3000 ton slug being placed into the firing chamber. In other words, stare down the moving thing in the middle of the room. Consequently, walking into the firing chamber will result in the Master Chief being fired out of the MAC gun to his death.

Aiming
The integration of the MAC to its hull means the entire warship or station must maneuver to aim the weapon. Even with an AI aiming the gun, the required precision and the 'dumb' nature of the ordnance fired means that hitting an evading target at 100,000 kilometers is extremely unlikely.

Firing
The firing process of a super MAC gun can be seen in the level Cairo Station.The process uses electromagnetism to fire a ferric-tungsten slug at high velocity. A huge amount of current is put through the first solenoid (coil of conducting wire) which creates a strong magnetic field which attracts the metal slug. As the slug passes into the solenoid, the solenoid is quickly turned off and the second solenoid, which is further up, turns on, which attracts the now high velocity metal slug just like the first solenoid, and the process is carried on. By the time the slug is fired out the end of the barrel it has been accelerated to a speed 40% of the speed of light. At the same time a pair of thrusters on the bottom side of the station fire for a couple of seconds to counteract the acceleration imparted to the station. The process then repeats. It normally takes five seconds to reload, which is why boarding craft have to be deployed to take the stations out.

Types

Standard Magnetic Accelerator Cannon
The standard ship-mounted MAC fires a 600-ton ferric-tungsten projectile with a depleted uranium core at 30,000 m/s (this is circa 2525 - MAC technology might have improved since). The large amount of energy needed to fire the weapon (the muzzle energy is 245 terajoules, to be precise) is particularly onerous on a warship, and the extended recharge time is a significant factor in combat against Covenant warships as multiple MAC rounds are required to penetrate Covenant shields. The standard MAC is sufficient to destroy any human vessel or severely damage an unshielded Covenant vessel. Even so, standard MAC rounds seem useless against the Forerunner Dreadnought.
The UNSC Spirit of Fire has been seen using its MAC cannon as a kind of orbital bombardment, firing 6 rounds within 9 seconds at a Scarab tank from orbit as well as armies and regiments of enemy infantry. However judging by the fast rate of fire, and the fact that two direct hits were required to down the Scarab, the Spirit of Fire's cannon may either be a variant that sacrifices power for a fast fire rate, uses smaller slugs, is a special version for orbital bombardments or is an earlier, weaker version of MAC.
An experimental version of the MAC was developed to fire three successive rounds on a single capacitor charge. A prototype was mounted on the UNSC Pillar of Autumn.

"Super" Magnetic Accelerator Cannon

A UNSC Defense Platform typically mounts a much larger and more powerful version of the standard MAC, nicknamed "Super MAC" or "the Big Stick."
These cannons fire a 3000-ton ferric-tungsten round at forty percent of the speed of light, impacting with a massive energy of almost forty-eight gigatons; powerful enough to penetrate and destroy most fully shielded Covenant warships. By receiving power from ground-based powerplants, orbital platforms could achieve recharge and reload times as short as five seconds. Due to prohibitively large power and sizing requirements, no UNSC ships are thought to be equipped with Super MAC guns.

M68 Gauss Cannon

The gauss-cannon is a UNSC weapon mounted on the Gauss Warthog. It uses MAC technology, but on a much smaller scale. It is used as an anti-armor weapon.

Speculation
Other MAC Sizes

Although never explicitly elaborated upon, there may be many more different sizes of MAC based on the sizes of possible mounts. For example, one might extrapolate that a frigate would mount a smaller, less powerful cannon than a supercarrier or a Marathon-class Cruiser, if only for power management issues.

Conceivably, a 'large' ship could mount many 'small' MACs. However, the lack of such occurrences might suggest that the power of a MAC, once the mass and volume of all attendant components (ex. capacitors) are accounted for, does not scale linearly. There is one known exception (destroyers), which are outfitted with two MAC cannons. The Pillar of Autumn had one large MAC cannon which could fire 3 600 ton rounds in sucsesion on a single charge.

Many believe that the MAC barrel is located near the underside of the ship, where there are three large plates. However, it is more likely that the barrel is located along the entire length of the ship. Logically, the multiple powerful magnets needed to accelerate a 600 ton slug to 0.1c requires an exceptionally long barrel, allowing for many magnets to affect the projectile. The huge 1.17 km length of the Pillar of Autumn would facilitate this, making the most likely muzzle location of the MAC barrel to be located at the protrusion at the ship's bow. This is also supported by the fact that if you look closly at the protrusion, you can see what looks like an openning.

Space Stations MAC Location

Further supporting the hypoe cargo elevator, the player can look up and visibly observe the Super MAC platform in action. The slug travels through the entire length of the tower, and exits at the "top" of the further nozzle. Later in the level, the player can notice the loading zone of the slugs at the base of the firing chamber.

Appearances

The following unit types mounted some form of MAC weaponry.
Halcyon-class Cruisers
Marathon-class Cruisers
Phoenix-class Colony Ships (wartime refit)
Orbital Defense Platforms
UNSC Destroyers
UNSC Frigates

Forerunner Dreadnought

"I've remotely destroyed our Keyships. A security measure. Without them I
cannot reach the Ark. But
neither then can the thing."
—Librarian to the Didact



The Forerunner Dreadnought, also known as the Keyship and colloquially known as the Forerunner Ship, was a Forerunner warship classification used in the Forerunner-Flood War.
They were also large part of the Forerunner strategy against the Flood, as they were the only vessels capable of activating the Portal to reach the Ark. One of these dreadnoughts would miraculously survive the Forerunner-Flood War and would become an integral part of the Covenant religion.



Specifications

The Forerunner Dreadnought is a geometric and angular warship, sharing many aesthetic features with other Forerunner constructs. Generally, it has a tetrahedral shape, with a forward, triangular prow, and, attached to it at equidistant points, are three similarly shaped struts to help ground the ship. Visually, its hull is grey or silver in color, and is estimated to be about 14 kilometers (8.699 miles) tall, 37,654 tons in weight, far heavier than leisure craft, but outweighed by a variety of transport and military vessels. The Dreadnoughts were an integral part of the Forerunner-Flood War, and were used as warships in confrontations such as the Battle of the Maginot Sphere, and were also used to travel through Portals to the Ark. Although their weapons systems were unknown, one Dreadnought was found and used by the San 'Shyuum during the Sangheili-San 'Shyuum War, and was far superior to Sangheili vessels of the time. During the Human-Covenant War, the same Dreadnought was resistant to even the heaviest of UNSC ship borne armaments, specifically the Magnetic Accelerator Cannon systems. The Forerunner Dreadnought has been known to carry over 1,000 beings, which is believed to be only a fraction of its full carrying capacity.


History
The history of the Forerunner Dreadnought is quite extensive, going back about 100,000 years.
Forerunner-Flood War
The Dreadnought was used extensively by the Forerunners in their war against the Flood. A number of Dreadnoughts were given to the Librarian, and combined with her ability to build Portals, the Librarian was able to transport herself back to the Ark with her Dreadnoughts if the situation required. The Librarian, however, bravely destroyed her Dreadnoughts to prevent them from falling into the hands of the Flood, who with them, would be able to instantaneously travel to the Ark, rendering the Halo Array useless. Near the end of the war, the Dreadnoughts were part of an unknown strategy to hold off the Flood for nearly 79 years, although this advantage would be foiled by the massive computing power of the Flood. At the Battle of the Maginot Sphere, Didact was in command of multiple Dreadnoughts, although near the end, when the Forerunners began generating Slipspace ruptures to destabilize the battlefield and destroy Flood craft, Dreadnoughts were recklessly piloted near the rifts, destroying them. However, at least one Dreadnought would survive the war and be rediscovered later by the Covenant.

Rediscovery
Early in the history of the San 'Shyuum, they found and worshiped the Forerunner Dreadnought. These early worshipers were split over the usage of the ship, as the Stoics refused to enter the vessel, while the radical Reformists wished to explore it. The Reformists then barricaded themselves within the Dreadnought, and left the San ‘Shyuumn home world, taking a gigantic piece of the planet with them.

Sangheili - San 'Shyuum War
After leaving their home world, the San 'Shyuum encountered the Sangheili, who also had familiarity with Forerunner technology. The San 'Shyuum believed that incorporating Forerunner technology was allowed by their religion. To the Sangheili, such a thing would have been unthinkable.
During the combat, the Sangheili had an early advantage, with each warrior comparable in skill to several San 'Shyuum in battle. However, the San 'Shyuum's technological superiority, and possession of the Forerunner Dreadnought, meant that they had the advantage in space, using the Dreadnought to great effect in devastating hit-and-run strikes against the Sangheilian Fleets. Eventually, the Sangheili were forced to amend their position of the treatment of Forerunner technologies and began incorporating elements into their own designs.
Eventually, in order to ensure the survival of both races, the two races merged to form the early Covenant with the San 'Shyuum as the head religious leaders and the Sangheili as their protectors and head of the military.

Writ of Union
The two races then penned the Writ of Union, which formally began the Covenant, and decommissioned the Forerunner warship, removing all known weapons, and placing it within the partially completed High Charity. It was then used to power the city, with its engines at partial power.

The Great War
Before the start of the Human-Covenant War, the Forerunner Dreadnought, the founding of the Prophet’s religion, would soon become the place where their religion was proven false. During the 23rd Age of Doubt, the Minister of Fortitude, and the Vice Minister of Tranquility went to the Forerunner Dreadnought for confirmation of two symbols found on the missionary vessel Minor Transgression. These two symbols were “Reclamation” and “Oracle”, which were found on what was known to Humanity as Harvest. After activating the "Oracle" inside of the Dreadnought, it began a series of cryptic messages, listed below:

LISTENED TO YOU MISINTERPRET
THIS IS NOT
RECLAMATION
THIS IS
RECLAIMER
AND THOSE IT REPRESENTS ARE MY MAKERS
I WILL REJECT MY BIAS
AND MAKE AMENDS
MY MAKERS ARE MY MASTERS
I
WILL BRING THEM SAFELY TO
THE ARK
FOR EONS I HAVE WATCHED

During this series of messages, the Oracle began a launch sequence, which would rip the Dreadnought from High Charity and destroy the artificial planet with it. The Oracle was disconnected, but this caused a spiritual crisis for Fortitude, Tranquility and the Philologist. Through the Oracle’s messages, the Forerunners (or their descendants), were still alive, which would shake the foundations of the Covenant itself to the core. In an attempt to keep the religion itself intact, they covered up the encounter, and would try and eradicate these Reclaimers.
For most of the Human-Covenant War, the Dreadnought remained a purely religious artifact, not a weapon, until the Battle of High Charity.

The Battle of High Charity

When the Flood attacked High Charity, SPARTAN-117 was on his way to stop the Prophet of Truth from escaping and at the end of the Battle of Installation 05. He was able to board the ship as Truth uncoupled it from the city's power grid by narrowly making it through a conduit and into the opening it connected to. The Forerunner Dreadnought lifted off, and slipspace jumped in the midst of a large three way battle between Covenant Loyalists, Covenant Separatists and the Flood.

Second Battle of Earth

Soon after it arrived in orbit around Earth, Lord Terrence Hood was about to give the order to destroy it. He only stopped because he found out that the Master Chief was aboard. The Forerunner Ship itself would soon become a battle ground as Master Chief tries to assassinate Truth.
Onboard the ship, Master Chief was contacted by a station on Io, but after going into radio silence, he killed four grunts, a pair of Jackals and then another group of four grunts. It is unknown what happened immediately afterward, but soon, Master Chief was found unconscious by a group of Brutes. The Brutes interrogate him, asking him where the Key of Osanalan is, when S-117 replies: “It means… always strip your enemy of weapons before you interrogate him”. The Brute looks down to see a plasma grenade, which soon detonates, killing him, a few other brutes and scattering the confused Unngoy. After making his way to the Prophet of Truth’s position, he reports to the UNSC that one Prophet Hierarch is on board and will transmit more information later. Then, Spartan-117 takes aim at Truth with a Covenant Carbine and fires.
Sometime afterward, Spartan-117 jumped from the Forerunner Dreadnought as it continued descending to Earth's atmosphere, falling two kilometers into the African jungle. The Forerunner Dreadnought continued its descent and landed on the portal to the Ark.
Though it is never explicitly stated, the Forerunner Ship is most likely a Key Ship, which would activate the Ark portal. This is evidenced by its apparent activation of the Ark portal on Earth while it was landing in the middle and Truth stating that the Ark portal on Earth is in its "true resting place" during game play.
The remaining UNSC forces on Africa planned to launch a surprise strike on the Dreadnought to eliminate Truth and stop it from activating the structure they thought to be The Ark. The Master Chief led a Marine assault on a Covenant loyalist anti-air battery sector in the town of Voi and successfully disabled the battery, giving the UNSC a clear shot at the Dreadnought. Lord Hood then attacked the ship with a squadron of Longsword fighters and three UNSC Frigates. The Dreadnought's advanced Forerunner armor allowed it to survive three MAC rounds and several missiles, and the UNSC attack was halted when the Portal was activated by the Key Ship.
After activating the portal, the Dreadnought entered it and landed on The Ark. It did not take part in the battle. The ship was possibly damaged beyond use from the combined effect of slipspace transition and the attack, and was most likely destroyed when the Halo destroyed itself. However, the fate of the Dreadnought is not known for sure.

Prophet of Mercy

"Halo! Its divine wind will rush through the stars, propelling all who are
worthy along the path to salvation."
—Prophet of Mercy



The High Prophet of Mercy is one of three Hierarchs that lead the Covenant High Council. He is by far the oldest. His birth name is Hod Rumnt.



Biography
He served as the Philologist on the Forerunner Dreadnought where he lead the priests prior to his ascension to Hierarch. He became the third Hierarch after the Oracle of the Dreadnought attempted to launch the Dreadnought during which time it referred to the humans as his creators. His tenure has been marked by several tense debates with Elite High Councilors over the proper dispensation of Forerunner artifacts. Mercy is considered one of the last of the old guard of the Prophets -- a hard-liner who publicly questioned the wisdom of the Prophets' demilitarization at the close of the Prophet-Elite War.
Being one of the eldest members of the Prophet triumvirate, Mercy is well-acquainted with the Covenant's governmental systems and its history. During a meeting with the Arbiter and the Prophet of Truth, he mentions a bit of Covenant history, referencing the Grunt Rebellion and the Taming of the Hunters.
He stayed by Truth's side after the death of Regret, and seemed to be more of a follower or supporter of Truth than an equal. As the Covenant Civil War began, Mercy still supported Truth's actions, even as it seemed that Truth was unraveling the very foundations of the Covenant through his extreme actions.
He and the High Prophet of Truth were attacked by the Flood on High Charity as they prepared to depart for Earth to begin the Great Journey. A single Infection Form made it past the Honor Guard Brutes, and latched onto his neck. Even as Tartarus attempted to save him, Truth intervened and let Mercy die, saying "The Great Journey waits for no one, brother. Not even you." Before his death, he was found by the Master Chief and questioned where Truth was going. He answered, "Earth, to finish what we started. And this time, none of you will be left behind." The Chief then killed the Infection Form, which had infected the prophet and with it, its host: Mercy.



Personality
Mercy can be seen as passionate and knowledgeable, as seen in the cutscene Sacred Icon where he shows his excitement about Halo expressing hope that the Great Journey should begin very soon. It's very possible that he has a sense of levity, seeing that he talked Truth out of condemning Regret as described on the level Regret, but that doesn't mean he doesn't know right from wrong. He is perceptible and a veteran of the Forerunners and their knowledge, he can be considered the Prophet of Truth's right-hand.

Harvest

Harvest was the seventeenth UNSC colony world, and one of the most remote. Located in the Epsilon Indi System, the planet had the unfortunate distinction of being the first human planet discovered by the Covenant. After disastrous First Contact, the planet was subsequently destroyed by the Covenant during the Battle of Harvest, and most of its population was killed due to the battle.

Population

Harvest was one of the UNSC's more productive and more peaceful colonies, within two decades of its founding it had the highest per capita agricultural manufacture of any inner colony. Major crops, such as corn, wheat, watermelons, peaches, apples, grapes, and numerous other foodstuffs nourished the inhabitants of more than half a dozen other colonies. The population of Harvest was three million but was destroyed by the Covenant in 2525 by invasion and orbital bombardment. The capital city and largest population center was Utgard, also home to Harvest's seven space elevators connected to the Orbital Space Station, Tiara.

Topography

Harvest was a small planet, approximately one-third the size of Earth with only a 4,000 kilometer (2,484 mile) equatorial diameter, slightly smaller than the Sol planet Mercury. In terms of surface area, Harvest possessed ~50 million km², roughly one-tenth the surface area of Earth. Harvest orbited Epsilon Indi extremely quickly, much faster than most UNSC colonies, at roughly 150,000 km/h, or ~41km/sec (by comparison, Earth orbits Sol at roughly 30 km/sec). Harvest had no natural satellites. Out of a total of five planets in the Epsilon Indi System, Harvest was the only habitable planet. The super-continent Edda dominated the planet, taking up roughly 67% of its surface. Two low-salinity seas covered the remainder of the planet, Hugin to the north, and Munin to the south. Almost 86% of Edda is within 500 meters of sea level, the only major change in elevation is Bifrost, a escarpment that "cuts" Edda in half.
Harvest's surface was once beautiful, covered in grassland and forests, lush fields and rolling hills, and a thousand lakes swarming with fish. The orchards were filled with fruit trees that were able to grow several different fruit on it at once. At one point during his service on Harvest Sergeant Johnson noted both apples and pears growing on the same tree. At night, bats filled the skies. After being glassed, the surface was reduced to a layer of melted glass, the destruction visible from orbit. The environment suffered a catastrophic blow as a result, with most species quickly going extinct on the world due to the destroyed environment. Soon, all that remained of Harvest's original natural ecosystem were the scavengers, feeding off the rotting remains of the planet's once abundant wildlife, and even they too soon perished.

History

In 2502, Avery Junior Johnson was involved in the assassination of Jerald Mulkey Ander, the head of the People's Occupation Government on Harvest as part of the ORION Project's Operation: KALEIDOSCOPE. Harvest was the first colony to be attacked by the Covenant and the first human world to be glassed. It was also the first time humanity had officially made First Contact with the Covenant.
In 2524 Sergeant Johnson returned to Harvest along with Staff Sergeant Byrne and Captain Ponder, all survivors of Operation: TREBUCHET, to train a Colonial Militia, and unbeknownst to them, fend off what UNSC had believed to be Insurrectionist attacks on ships in the systems.
On February 3rd 2525 The Harvest Long range orbital platform made radar and spectroscopic contact with Minor Transgression. Contact with Harvest was lost thereafter.
By April 12th 2525 the Colonial Military Administration sent the scout ship Argo to investigate, other then confirming its arrival at Harvest no other transmissions were sent, and Argo was presumed MIA.
On October 7th 2525 Fleet Command assembled a battlegroup to investigate, due to the fact that the Harvest situation was deemed to have become serious. The battlegroup consisted of the destroyer Heracles, commanded by Captain Veredi, as well as the frigates Arabia and Vostok. They enter the Harvest system only to find the planet glassed, The Vostok and Arabia were lost with all hands while the Heracles jumped out of the system, but took several weeks to return to Reach due to damage sustained in the battle.

Escape from Harvest

The citizens of Harvest soon found themselves in the middle of the first battle between the Covenant and humanity, using their newly trained Militia to herd hundreds of thousands of civilian survivors from Gladsheim, Vigrond, and other locations to the Utgard Space Elevators to escape the planet. During the first Covenant attack on Harvest about +250,000 humans managed to escape the planet by packing into 236 freight containers which were then loaded into seven elevator depots in Utgard. Every five to seven minutes, seven pairs of freight containers were loaded into the Space Elevator. Loaded ahead of these freight containers were seven "grease buckets", maintenance containers, two which were loaded with Johnson's men and Jilan al-Cygni. The other five were decoys rigged with claymore mines which were used to soften the Brutes, Grunts and Drones which had boarded and taken control of Tiara. While the other two "grease buckets" holding Johnson and Co. stopped and they were fighting off the Covenant, the number seven strand of the Space Elevator snapped a few thousand kilometers above its anchor due to the stress caused by the load becoming unbalanced. There were 11 pairs of freight containers on the strand when it snapped, killing around 20,000 people. The remaining freight containers carrying the survivors of Harvest continued up the elevator, out into space, where they met up with propulsion pods that Sif had placed previously. Once Johnson and Co. finished fighting the Covenant on the Tiara, they joined the survivors and used the propulsion pods to enter Slipspace. In these freight containers was at least one future member of the Spartan-III project.

The Battle of Harvest

Vice Admiral Preston Cole fought in and barely won the Battle of Harvest in 2531, six years later. This battle was the single most titanic battle ever fought by the two opposing forces before the Fall of Reach in 2552, and resulted in the creation and implementation of the Cole Protocol. The UNSC was able to retake the planet but with the massive loss of 2/3 of their fleet.

Prophet of Regret

I shall light this holy ring, release its cleansing flame, and burn a path into
the divine beyond!"
—Prophet of Regret

The High Prophet of Regret is the youngest of the three High Prophets that lead the Covenant High Council.

Biography
Twenty Third Age of Doubt
During the Age of Doubt, 2524 by the UNSC calender, the Prophet of Regret was known as the Vice Minister of Tranquility. He was unique amongst his Prophet fellows in his confrontational attitude and combative demeanor, a trait he had gained from spending a good deal of time working with Elites. He was the first to inform the future Prophet of Truth about the existence of Harvest and what they believed to be a vast reliquary of Forerunner artifacts (In reality, these "artifacts" were nothing less than the humans on the planet, or "Reclaimers"). After persuading the future High Prophet to join him in a conspiracy to gain these artifacts for their own private usage, he helped Truth in his plans by pretending to sympathize for those blacklisted from reproducing due to inborn genes, which included the then Hierarch Prophet of Restraint. After pretending to be the father of an unlawful child the Prophet of Restraint had fathered, Regret forced Restraint out of power by threatening to reveal the scandal if he did not leave his position as High Prophet.
Before their coup, the Prophets visited an "Oracle" within the Forerunner Dreadnought, an ancient AI known as Mendicant Bias that had stored itself in the ship and had not spoken to anyone for several hundred years. When the Luminations of Harvest were entered into its matrix, it suddenly came to light and revealed the symbols had been misinterpreted-that humans stood as equals to the Forerunner, and the Covenant had been mistaken in their beliefs. As it tried to launch the Dreadnought from High Charity, the Prophets along with the Philologist, leader of the ascetic priests and later the Prophet of Mercy, disconnected the Oracle from the ship and decided that the humans must be eradicated once and for all, before any of the Covenant could learn of this and shatter their entire existence.
He served during the destruction of Halo Installation 04 and was one of those who publicly condemned the Sangheili Commander who was responsible for the loss of the ring. While he appeared for the trial, it was by way of hologram, as Regret was en route to Earth, searching for a method to initiate the Great Journey.

On the Path to the Great Journey
Earth
"The message just repeats, "Regret, Regret, Regret.""
—Cortana
Despite being chided by his two compatriots, The Prophet of Regret led the first attack on Earth. His fleet was small for an assault, totaling only two Assault Carriers and thirteen CCS-class Battlecruisers. It is thought that he was directed to Earth by a Forerunner artifact, perhaps the one on Coral to search for the Ark, but he apparently had no knowledge of a human presence on Earth and that it was his enemy's home world. Nevertheless, he sent Ranger Elites and Boarding Craft to destroy the Orbital Defense Platforms Malta, Athens, and Cairo, so he could push through into the heart of Africa. Despite the Master Chief's actions, his ship made it to the ground and deployed the first full-scale invasion force of Covenant on Earth.
After landing in New Mombasa to search for the Forerunner artifact located on Earth, Regrets forces deployed numerous ground units to further search the city, including at least two Scarabs and many Phantom dropships. As Spartan-117 approached his Carrier, Regret's ship initiated a Slipspace jump right in the middle of New Mombasa to escape his pursuers and regroup his attack force. The move was so surprising that only the UNSC In Amber Clad and four Prowlers were able to follow the Carrier as it jumped and destroyed the city.

Delta Halo
"I shall light this holy ring, release its cleansing flame, and burn a path into the divine beyond!"
—Prophet of Regret
Regrets Carrier landed ground and infantry forces onto the surface of Installation 05, and the Covenant, under Regret's say so set up a presence around a "temple" in the middle of a lake, from which Regret began his religious sermons. He also transmitted an apology to the Prophet of Truth, indicating that he couldn't have known that the humans would be there or in such force. Truth responded by saying that only Mercy had spared him from "public" condemnation. Nevertheless, High Charity and the Second Fleet of Homogeneous Clarity rushed to the new Halo, and a flight of Phantoms was deployed to rescue the Hierarch.
The In Amber Clad arrived in system soon after and deployed ODST forces onto the surface of Installation 05 along with the Master Chief to locate and kill Regret. The operation was a success, but soon afterward High Charity made a jump to the ring and ordered one of the nearby ships to use its Gravity Lift to destroy the temple, nearly killing the Spartan and negating any chance of rescue for the Prophet.

It isn't known how Regrets body escaped the destruction of the temple, but it was later assimilated by the newly formed Gravemind, reanimated and incorporated into the creature itself. He made a final appearance at the beginning of the next level, where he expressed annoyance with another captive of the Gravemind's, 2401 Penitent Tangent, and reacted to the presence of the Arbiter, warning the Arbiter to forgo any heretical suggestions made by the Monitors and the humans and to pursue the Great Journey.

The Ark
Throughout the events of Halo 3, Regret likely remained a part of Gravemind. If this is true, then Regret was finished for good on the Ark, where the Gravemind was killed due to the activation of the replacement of Installation 04.

Personality
Based on a letter written from Truth to Mercy relating to his untimely attack of Earth without realizing the significant human presence and defensive measures, Regret is considered a very rash and ambitious Prophet, immature and naive compared to the other ladder members. He developed a habit of ingesting excess alcoholic beverages, and his work as Vice Minister of Tranquility meant that his duties brought him into regular contact with the Sangheili, and had adopted some of their personal traits, such as a preoccupation with honor and personal arms. During their visit to the Oracle upon the Forerunner Dreadnought, Regret, then still a Vice Minister, first tried to threaten a Lekgolo pair with a Plasma Pistol and then almost shot the Philologist, later to become Mercy, for "tampering" with the Oracle.

Combat
The only weapon Regret has is his Gravity Throne. It is only seen being used as a weapon in Regret. Regret's gravity throne is equipped with two Gravity Cannons that glow bright red and are a modified version of a Hunters Fuel rod gun. It is also equipped with a teleportation device that allows him to teleport a short distance away. The only way to defeat him is to board his throne and melee attack him. However, rockets will lock onto the throne as if it were a vehicle. Though this will not kill the Prophet, enough rockets can hurt him, reducing the number of hits he can take once you board his throne. Also a lunge with the energy sword will weaken him, though not as much as a rocket.
After a few hits, he will throw you off and teleport away, and his throne must be re-boarded to resume the assault. This pattern will repeat until either he or the Master Chief dies.
Regret is not alone, however. Throughout the battle with him, Grunts and Honor Guard Elites will attempt to aid him against the Chief.
Due to a glitch, Regret can be knocked out of his throne and shoot you with a plasma pistol that has a faster rate of fire for a few seconds. Regret will then teleport back to his chair as if nothing had happened.

UNSC In Amber Clad

The UNSC In Amber Clad (FFG-142) was a United Nations Space Command Frigate.

History

First Battle of Earth

As of October 2552, the In Amber Clad was commanded by Commander Miranda Keyes. It was docked with Orbital Defense Platform Cairo during an award ceremony. In the middle of the ceremony, however, a Covenant Fleet appeared around Earth and so the First Battle of Earth began. Home Fleet ships then began to open fire on the Covenant Ships. Though the In Amber Clad did not engage in direct combat over Earth, they did descend to catch John-117 after his daring destruction of one of the Covenant's Assault Carriers using their own bomb.

First Battle of Mombasa

Afterwards, the vessel descended to Mombasa, Kenya, where it dispatched numerous units from the 17th and 77th Marine Regiments. During the battle, the In Amber Clad was the headquarters for all UNSC forces in the area. The ship also reinforced and resupplied the Marines with armor, ground support, and more troops. The IAC also began to evac and treat injured and wounded Marines.
As the High Prophet of Regret suddenly initiated a Slipspace jump inside the city, the In Amber Clad was one of the only vessels close enough to follow it. Fleet Admiral Sir Terrence Hood allowed Keyes to follow the Assault Carrier through the Slipspace rupture, even though she did not know where it was headed.
The UNSC Coral Sea, UNSC Dusk, UNSC Paris, and the UNSC Redoubtable were sent to follow and assist the In Amber Clad with the heavy Assault Carrier.

Battle of Installation 05

The In Amber Clad ended up at Installation 05. There, Keyes immediately sent John-117 and her contingent of Marine Shock Troopers to the surface in Human Entry Vehicles to track down the Prophet of Regret at the Temple, while she took herself, Johnson and the 77th Marines to the Library in order to retrieve the Index and prevent the Covenant from activating Halo.
As Keyes entered the Library, they were immediately attacked by the Flood and most of her Marines were taken by the flood and became Combat Forms and Carrier Forms, only a few eventually making it to the index. However, Keyes, Johnson, and what was left of the Marines were ambushed by the Arbiter only a few seconds after retrieving the index.
It is likely that the Flood commandeered a Pelican and infiltrated the In Amber Clad, as it was not seen again until it crashed into High Charity. At this point the Flood controlled the ship. It is speculated that Gravemind was aboard.

First Battle of High Charity

The ship crashed into a tower near the Council Chamber and immediately the Flood used most of the ship's remaining Pelicans to spread out over High Charity, often crashing the ships to inflict maximum damage on the city. The Flood quickly assimilated most of High Charity's population. At this point, the ship was out of commission, designating it as destroyed.
Cortana intended to use the In Amber Clad's engines to destroy High Charity, but it was never done. It is unclear whether she still could do it because during the Battle of Installation 00, Cortana was unable to stop the Gravemind from using High Charity to travel through the galaxy. It is assumed to be completely destroyed when John-117 blasted the station's reactors causing them to go critical.

Installation 04

Installation 04 was one of a series of gigantic ring worlds (the Halos from which the series gets the name) apparently left behind by the enigmatic, technologically-advanced, and apparently extinct Forerunners. The Covenant reverentially described Installation 04 as either the First Holy Ring, or the First Sacred Ring. 04 is also known colloquially among Halo fans as Alpha Halo. It is the main setting of the first Halo game, Halo: Combat Evolved. After its destruction at the end of the Battle of Installation 04, The Ark started to make another Installation 04 after the first Installation 04 was destroyed.

Background

The purpose of Installation 04, along with its sister installations, was to preclude and thwart the parasitic lifeforms known as the Flood from consuming the galaxy's sentient life. In the event of a Flood outbreak, one of the seven installations could be triggered to annihilate all sentient life. Once a ring is set off all remaining rings would activate.
Installation 04, until its destruction by the Master Chief, was controlled by the Forerunner artificial intelligence construct (Monitor), 343 Guilty Spark.

Climate

The climate of Installation 04 is very similar to Earth's climate. There have been hurricanes over the oceans on the ring. The weather is, however, extremely unpredictable - rain and snowfall can occur at random, leading some to wonder if the weather is intentionally irregular, or whether there is some indiscernible pattern.

Ancient History

Installation 04 was built by the Forerunners at approximately 98,665 BCE (It was about 101,217 years old in 2552 CE).

Part of the wreckage of Installation 04
The Installation was activated sometime thereafter, and all Forerunner and Flood were killed. Installation 04 lay dormant for millenia, with 343 Guilty Spark and his Sentinels ready to keep the Flood confined in the Flood Containment Facilities and keeping the infrastructure of the Halo in perfect working order.

Destruction

"Halo... It's finished...""No. I think we're just getting started."
— Cortana talking
to the Master Chief after the
destruction of Installation 04.

The Covenant discovered the location of Installation 04, after the Covenant Fleet of Particular Justice followed the single UNSC cruiser, the UNSC Pillar of Autumn, which was fleeing from the Battle of Reach through slipspace. It is assumed that the Covenant knew about the Ring as the Prophets all have a holographic representation of them on their headdresses and Cortana saying previously that she used the coordinates received by the beam in The Fall of Reach. Due to the Covenant's faster Slipspace capabilities they arrived before the Autumn.
The Pillar of Autumn arrived around September 19, 2552 and was promptly shot down by warding Covenant space forces. At around the same time, the Covenant ground forces on 04 accidentally unleashed the Flood from captivity. The ensuing four-day melee that took place all over the ring was called the Battle of Installation 04. Humans, Flood, and Covenant fought massive battles against one another as the Forerunner Constructs tried to control the outbreak by activating the Halo. In the end a single human, SPARTAN-117, detonated the Autumn's fusion reactors which destroyed the Halo.
Only a handful of humans and Covenant survived the battle. 343 Guilty Spark floated through space until he met a group of Covenant on Threshold. Inspired by his words, they began a Heretic rebellion against the greater Covenant. Installation 04's destruction is seen as the first step in the chain of events that led to the Covenant Civil War. The Installation 04 was the first Halo destroyed.
There is now a large field of debris where Installation 04 was, though a few large chunks of the ring remain. Some smaller pieces of the Installation 04 have landed on Basis and others have burnt up in Threshold's atmosphere on entry.

Replacement

Shortly after the destruction of the Halo, the Ark began to automatically construct a new Halo to replace Installation 04. This exact copy of the first Halo ring was nearing completion only a few months after the first ring was destroyed, but was subsequently also destroyed when it was fired before it was ready by the Master Chief and Cortana.

Astronomy

The "Ringworld" of Halo is much smaller than Larry Niven's Ringworld, by a magnitude of 3,000. While the diameter of Niven's ringworld is close to the diameter of Earth's orbital of 300,000,000 km, the 10,000 km diameter of Halo is much closer to the diameter of Earth itself, which is 12,756 km. Ringworld has a star similar to our sun in its center, and Halo is orbiting a planet, but does not encircle it.
Circumstantial evidence from Bungie indicates that Alpha Halo may be located in the Iota Horologii System, only 50 Lightyears from Earth.

Speculation

It is unclear why the gas giant Threshold was specifically chosen to be the planet which Installation 04 orbited, but it is supposed that the large number of Forerunner machines already operational in Threshold (explicitly the network of Gas Mines), may have played a role in their decision. It could also be because it was the only planet in the system that had enough gravity to hold Halo in place.
Another common theory is that it was placed there mathematically in order to cover the whole of the galaxy with the spread of the Halos' main weapon. It is probable that the Forerunner had chosen Threshold as the staging point for constructing Installation 04 in a failsafe to attempt to isolate any major Flood outbreak. It may have been as simple as its proximity to the Gas Mine stations on Threshold, which the Forerunner may have used for power.