Forerunner fleet

The Forerunner Navy was a branch of the Forerunner Armed Forces. It was led by Forerunner Fleet Command and was in charge of all space combat and naval operations. They held the responsibility of protecting Forerunner planets from space from the Flood in the Forerunner-Flood War.

Units
The last known actions of the Suppression, Security, and Emergency Circumstance Fleets were in an engagement against the Flood-controlled fleets in a last stand during the Battle of the Maginot Sphere
 * Primary Pioneer Group
 * Advance Survey Team Alpha
 * Suppression Fleet
 * Security Fleet
 * Emergency Circumstance Fleet

History
It is unknown exactly how many ships that the Forerunners had in their fleet, but given that a single AI (Mendicant Bias) would take personal command of a core fleet alone of one thousand ships, it is fair to assume that the Forerunner fleet consisted of many thousands of ships, though this number was severely whittled down over three centuries of war. During the course of the war, the Forerunner fleet attempted to prevent the Flood from landing on the surface of various planets, and when the Flood invariably did, the Forerunner Navy's main concern was to evacuate as many civilians as possible.

As the Forerunners realized that they had no chance of militarily winning the war, and as the Flood closed in on the Maginot Sphere, they created a master AI, Mendicant Bias, to coordinate all of their strategic movements and grapple with the Gravemind itself. Mendicant Bias was given a personal fleet of a thousand core capital ships. However, direct contact with the Gravemind caused Mendicant Bias to turn rampant, and it quickly turned on its creators.

Mendicant Bias led its fleet through the Maginot Sphere, where it encountered three entire fleets of Forerunner warships led by Offensive Bias. The following encounter was quite possibly the largest battle ever seen by the galaxy ensued between the two opposing sides. At this point, Didact, overall commander of the remaining Forerunner Navy, fired the Halo Array. Although it killed all the surviving Forerunners, it also neutralized Mendicant Bias's giant Flood-controlled fleet, which had until this point, vastly outnumbered Offensive Bias. With the odds much more even, Offensive Bias managed to defeat the rampant AI's remaining core ships and attempted to deliver Mendicant Bias to the Ark for study.

What happened to the few surviving Forerunner ships after this is unknown, but without any Forerunners to guide them, some of them may have crashed onto various objects and were later found by the races of the Covenant, some utilizing the ships' advanced technology. For example, the Forerunner Dreadnought was used to power the Covenant capitol of High Charity.

Known Commanders

 * Mendicant Bias
 * Offensive Bias
 * Didact

Ship Types

 * Dreadnought or Keyships and other forms of vessels, such as cruisers.
 * The vessels found inside the Shield World by the UNSC Spirit of Fire are described as Forerunner Dreadnoughts. However, they differ greatly from the Keyships and are most likely a type of heavy battlecruiser in the Dreadnought class.

Ship Capabilities
Based on what was seen of them in the games, Forerunner Dreadnoughts and Keyships were massive and extremely well protected and powered.

During Halo 2, it was seen that a single Dreadnought could power a structure the size of an entire moon; in Contact Harvest, it is further noted that this only required a fraction of its total power output. In Halo 3, an entire battlegroup of UNSC Frigates fired their MAC Cannons at it, but the Dreadnought escaped with no damage whatsoever. This makes it even more powerful than a Covenant Supercruiser, which could only barely take the impact of three special light MAC rounds and five hundred Archer missiles. However, it has never been seen to use its actual weapons.

Known Units

 * The Forerunner Dreadnought, which was activated in Halo: Contact Harvest.
 * Unnamed Forerunner Starship, only seen in the Flood-controlled Shield World.

Trivia

 * The Forerunner Navy fought the Flood during the Flood-Forerunner war.
 * A Forerunner ship was used to power High Charity for the greater part of the Covenant's history.