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This article is about the cut Halo 2 campaign level. For other uses of the term "Forerunner tank", see Forerunner Tank.
"forerunnertank" was the working title for a series of two campaign levels cut from Halo 2. The missions would have served as successors to the Quarantine Zone mission, showcasing the Master Chief and the Arbiter's introduction to the Gravemind.
While making Halo 2, Bungie developed pairs of levels under single names - such as Outskirts and Metropolis being originally created as one level named "Earth City". Forerunnertank was seemingly similar in this regard, seemingly intended to comprise of two individual missions in which the player would alternate between playing as Master Chief and the Arbiter (then-known in development under the name Dervish).
The mission was first discussed on the Halo 2 cutscene commentary contained in the Halo 3 Legendary Edition's Halo 2 cinematics commentary. In the commentary, the mission is discussed by Joseph Staten and Jason Jones, who express their despair from the amount of issues encountered during the level's creation. The level was intended to take place after the level Quarantine Zone, and showcase the Master Chief's journey through the Sentinel wall and the bowels of Installation 05 - something largely not present in the final game. The details explained in the developer commentary line up with many of the storyboards showcased by Lee Wilson, and as such many parallels can be made.
The storyboards posted online by Lee Wilson show a slightly different series of events regarding the battle in the quarantine zone area; a seemingly-alternate end to the Quarantine Zone mission showcases a team consisting of Avery Johnson, Miranda Keyes and Master Chief in the quarantine zone above a "thermal outtake platform" - near the site of a crashed Pelican. The trio are attempting to repair a damaged radio to little success, before being ambushed by the Arbiter. Due to the early era in which these storyboards were produced, the Marines still wear their Combat Evolved-design uniforms, and the Arbiter wears a regular combat harness rather than his Arbiter body armor.
The Master Chief and Arbiter engage in a fistfight before being interrupted by the arrival of a Covenant Phantom, staffed by Tartarus and his Brutes. The Brutes make their way toward the humans, but are themselves interrupted by the emergence of the "Flood Hulk" - seemingly an early design idea for what would later go on to become the Flood Juggernaut. Notably, the Hulk appears to reuse the design of the Sharquoi, originally featured in Marathon and cut from Combat Evolved.
The Flood Hulk is fired upon by all sides, though it does manage to take a swipe at Tartarus' Phantom - but is ultimately defeated and falls onto the platform - which collapses under the weight. The Hulk, two Brutes, the Arbiter and Master Chief all fall into the pit, with the Chief landing successfully and picking up a Brute Shot - before fading to gameplay. This cutscene may coincide with the cutscene mentioned in the Halo 2 developer commentary by Staten, as similary-large to the Gravemind opening cutscene and ultimately cut.
The second set of storyboards then seem to focus on the outro of this level, depicting the Master Chief creeping around in the "Gravemind's lair" with a battle rifle. He walks around a few corridors before stumbling onto the Gravemind and being captured. These storyboards are labelled in their original filenames as "intra" - a standard used for cutscenes which take place between two subsequent missions (such as the cutscene in the middle of the levels The Arbiter and The Oracle).
The final set of storyboards then seem to focus on the Arbiter's encounter with the Gravemind. The Elite attempts to stay hidden while observing the Gravemind's talk with the Master Chief by hiding behind a pillar - which is then revealed to be a large tentacle. The Arbiter is captured and the cutscene then proceeds to play out in a similar fashion to the opening cutscene of the Gravemind level in the final game. A few changes are present such as the addition of Flood forms (including a more finalised design of the Juggernaut) throwing corpses into the Gravemind's pit.
Little is known of the Forerunner tank's intended gameplay, though a few details were discussed in the developer commentary. This level was intended to serve as the proper introduction for the Gravemind character, and feature the Gravemind's tentacles throughout the mission periodically slamming down at the player and moving behind doors like "racing freight trains". The level was to involve the titular "Forerunner Tank" - a large Forerunner vehicle (or large Sentinel variant akin to Halo 3's cut Strato-Sentinels) which would have been - as described by Jones - "... awesome, that blows things up, glows a lot from little windows and moves real fast.". The geometry for the Forerunner Tank was later reused in the level Quarantine Zone as the Gondola which the player rides near the end of the mission. Some of the technology developed for the Gravemind's tentacles was to be later reused in the High Charity level, in which the tentacles would reappear and smash through the windows encountered in the mission.