From Halopedia, the Halo wiki
The "Preserve" chest piece features two large armour plates which curve downward from the user's shoulders, towards the centre of their chest. At the join between these two plates, there is a wedge-shaped protrusion pointing downwards, directly beneath the user's head. Additionally, below the left and right plates, there is an additional piece of armor on either side, just above where the wearer's ribcage would end. These meet beneath the wedge-shaped protrusion, at the user's solar plexus, where there is a piece of unidentified apparatus jutting out of the front of the armor.
During the production of the Defiant Map Pack, two additional armour sets were also produced, codenamed
The existence of the "Preserve" chest piece was not discovered until modder Gamecheat13 uncovered customisation renders of these two cut armor sets in the game files of the second Halo Insider flight (dubbed the "FireFlight") of Halo: The Master Chief Collection's PC port of Halo: Reach, in 2019. The "Preserve" chest piece was not featured in the port at launch, however.
Eventually, in September 2020, 343 Industries confirmed that the chest piece had been finalised and polished for inclusion in the game, would be available as part of Season 4: Reclaimer of MCC, alongside all of the other armor pieces from the two sets: AKIS, EXO/TSCS and Mariner. However, difficulties encountered during development meant that the armors were not deemed to have reached a high enough quality standard in time for inclusion into Season 4, so the armor piece was pushed back to an unspecified later season.
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