Anodyne Spirit

Forerunner Keyship "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 Keyship, Terminal Four and colloquially known as the Forerunner Ship, was a Forerunner warship classification used in the Forerunner-Flood War.

They were also a 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 Keyships would miraculously survive the Forerunner-Flood War to be found and used by the Prophets, and would later become an integral part of the Covenant religion.

Specifications
The Forerunner Keyship 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 gray 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 Keyships 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 Keyship was found and used by the San 'Shyuum during the Sangheili-San 'Shyuum War, and was far superior to Sangheili vessels of the time. At the time of the Human-Covenant War, the same Dreadnought was completely impervious to even the heaviest of UNSC ship borne armaments, specifically the Magnetic Accelerator Cannon systems. The Forerunner Keyship has been known to carry over 1,000 beings, which is believed to be only a fraction of its full carrying capacity.

It consists of thousands of rooms, many of which are docking bays and control rooms, including a command chamber where the Prophet of Truth resided which was many stories high. It has many lift rooms which were similar to the ones in the towers in the Halo 3 level The Covenant. It most likely has many engine rooms as well.

History
The history of the Forerunner Keyship is quite extensive, going back about 100,000 years.

Forerunner-Flood War
The Keyship was used extensively, by the Forerunners in their war against the Flood. A number of Keyships 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 Keyships if the situation required. The Librarian, however, bravely destroyed her Keyships 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 Keyships 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 Keyships, although near the end, when the Forerunners began generating Slipspace ruptures to destabilize the battlefield and destroy Flood craft, Keyships were recklessly piloted near the rifts, destroying them. However, at least oneKeyship would survive the war and be rediscovered later by the Covenant.

Rediscovery
Main Article: San 'Shyuum Civil War

Early in the history of the San 'Shyuum, they found and worshiped the Forerunner Keyship. 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 Keyship, and left the San 'Shyuum home world, taking a gigantic piece of the planet with them. This piece was later refitted into the rocky dome of High Charity along with the Keyship atop it.

Sangheili - San 'Shyuum War
Main Article: 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 ten San 'Shyuum in battle. However, the San 'Shyuum's technological superiority, and possession of the Forerunner Keyship, meant that they had the advantage in space, using the Keyship 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.

Human-Covenant War
Main Article: Human-Covenant War

Before the start of the Human-Covenant War the Forerunner Keyship, 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 Keyship 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 Keyship, it began a series of cryptic messages, listed below:
 * FOR EONS I HAVE WATCHED
 * 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

During this series of messages, the Oracle began a launch sequence, which would rip the Keyship from High Charity and destroy the Covenant capital 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 to eradicate these Reclaimers.

For most of the Human-Covenant War, the Keyship 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, the Master Chief 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 Keyship lifted off, and jumped into Slipspace in the midst of a large battle between Covenant Loyalists, Covenant Separatists and the Flood.

Second Battle of Earth
Soon after leaving High Charity (infected by the flood) it arrived in orbit around Earth, Lord Terrence Hood was about to give the order to destroy it with the orbiting Super MAC guns. He only stopped because he found out that the Master Chief was aboard. The Keyship itself would soon become a battle ground, as Master Chief tries to assassinate Truth.

On-board 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 John-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 Unggoy. 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. Just before the Master Chief gets a good shot at Truth, a Jackal with a Carbine shoots and hits the Chief.

Sometime afterward, John-117 jumped from the Forerunner Keyship as it continued descending to Earth's atmosphere, falling two kilometers into the African jungle. The Forerunner Keyship continued its descent and landed on the Portal to the Ark.

Though it is never explicitly stated, the Forerunner Ship is 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 Keyship 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 Keyship. Lord Hood then attacked the ship with a squadron of Longsword fighters and three UNSC Frigates. The Keyship's advanced Forerunner armor allowed it to survive three MAC rounds and several missiles completely unharmed, and the UNSC attack was halted when the Portal was activated by the Key Ship.

After activating the portal, the Keyship 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 Keyship is not known for sure.

Halo Wars
Forerunner Dreadnoughts also make their appearance in Halo Wars cutscenes, in which a huge fleet of Dreadnoughts are stored in The Apex of an unknown Shield World, waiting for a Human to activate them via a control panel located on a platform. Prophet of Regret and Ripa 'Moramee were intended to use the ships against humanity, as the "Ancients have granted them an unparalleled fleet". It has to be noted that these ships were totally different than the keyship which was inside High Charity.

Before they had the chance to use them, the crew of Spirit of Fire decided to destroy the ships and the shield world by making the artificial sun of the planet to go supernova.

As a result, all the Dreadnoughts inside the planet were destroyed by the massive explosion.

Trivia

 * The Threshold Gas Mine hangar bay looks similar to the Dreadnought's hangar and has a Seraph as depicted in Halo 2.
 * According to the account by Forerunner AI, Offensive Bias, in the sixth Terminal, he controlled Dreadnoughts exactly 37,654 tons (75,308,000 pounds) each, in his battle with the Mendicant Bias. This may be the same class of ship although it is likely it was a special class of Dreadnought designated the Key Ships.
 * Gemini is the only multiplayer level that one can see the Forerunner Keyship in.
 * The Forerunner Keyship is said to be even faster than all Covenant cruisers, all of which can outrun all Human vessels.
 * Originally, a level referred to as 'Forerunner Ship' was supposed to take place on the vessel right after defeating Tartarus in Halo 2, as said in Halo 3 Essentials.
 * It was featured in the Halo: Uprising comic series. You can see the inside of the Dreadnought only in those Halo comic books.
 * The Covenant were only able to use 10% of the Dreadnought's generator to power High Charity.
 * The ships in Halo Wars are referred to as Dreadnoughts, besides looking rather different, this may be a fault, an other type of Dreadnought or a simple unassembeled version.