Steel Skin Pack
From Halopedia, the Halo wiki
The Steel Skin Pack is a Downloadable content pack for Halo 4 that includes steampunk-inspired skins for all loadout weapons. It was released on August 20, 2013, for $2.99 USD by itself or included as a part of the Champions Bundle.
The contents of the Steel Skin Pack were not available for use in the Halo 4 component of The Master Chief Collection at launch, though were eventually included in the collection as part of the Battle Pass system in Season 4: Reclaimer.