From Halopedia, the Halo wiki
The DECIMATOR is the closest GEN2 armor variant to the MJOLNIR Mark VII, and features a versatile energy shielding system that can be partially reshaped and sculpted. Like the Mark VII suit worn by Naomi-010, DECIMATOR's physical architecture closely resembles MJOLNIR Mark V [B].
The DECIMATOR-class Mjolnir is an attempt by the Office of Naval Intelligence's Materials Group to re-engineer major improvements of the Mjolnir Mark VII prototypes into the second generation of the MJOLNIR Powered Assault Armor. The most successful of these efforts is the DECIMATOR armor's sophisticated energy shielding system. Elements from DECIMATOR would later go on to be used in Project KEYSTONE.
Halo 5: Guardians
First mentioned in Canon Fodder Issue 48 "Reqlamation Begins", the DECIMATOR-class Mjolnir was later confirmed to appear in Halo 5: Guardians in Canon Fodder Issue 50 "Fifty Caliber". On February 24, 2016 the armor was made available in the Hammer Storm update for Halo 5: Guardians.
List of appearances