Forerunner Tank was a proposed level in Halo 2's Campaign that was cancelled during the production phase of the game. The level was only revealed on the Halo 2 cutscene commentary contained in the Halo 3 Legendary Edition's first Bonus Disc.
The purpose of the level was to tie in plot between the end of the level Regret and the cutscene after the end of the level Quarantine Zone. The level was said to be placed after the cutscene in Quarantine Zone where Thel 'Vadamee is pushed down the index chamber by Tartarus and before the cutscene where Thel meets John-117 and talks to the Gravemind. This level was supposed to be the Gravemind's introduction. The level's replacement was the short cutscene at the end of Regret; the level's removal resulted in the long series of different cutscenes between Quarantine Zone and Gravemind.
In the level, the Gravemind's tentacles were going to slam down all around the player, and move behind doors like "racing freight trains".
The level would have described John-117's adventure through the bowels of Delta Halo before his eventual capture by the Gravemind. The "Forerunner Tank" providing the namesake of the level was only described as something "... awesome, that blows things up, glows a lot from little windows and moves real fast.". When asked why he wanted the Forerunner Tank level in the game, Jason Jones' response was, "Awesomeness would ensue.".
- In the Halo 2 level Sacred Icon, the gondola is a heavily modified piece of moving geometry originally intended for Forerunner Tank.
- If you open the BSP Geometry for the Gravemind cinematic by using modding tools for Halo 2 Vista, there is an entrance that was never shown that would have been used for this cut level.