From Halopedia, the Halo wiki
The FJ/PARA is a variant of the MJOLNIR Powered Assault Armor.
Compatible with the Mark V, the FJ/PARA shoulder pauldrons and knee guards were designed specifically for airborne units, with the purpose of maximum protection with minimum weight. In 2552, Kat-B320 of NOBLE Team wore the FJ/PARA shoulder pauldrons. Four other members of NOBLE Team wore the FJ/PARA knee guards: Carter-A259, Jun-A266, Emile-A239, and Thom-A293. After the Human-Covenant War, the knee guards of NOBLE-, VIGILANT-, and Wrath-classes Mjolnir featured physical architecture similar to FJ/PARA knee guards due to the armors being recreations of custom armors which belonged to the Spartan-IIIs from NOBLE Team. Similarly, the shoulder pauldrons of INTRUDER-class Mjolnir also resembled the FJ/PARA shoulder pauldrons of Kat-B320's armor.
The FJ/PARA armor types are unlockable in the game's purchase system via the use of cR. In Halo: The Master Chief Collection, the FJ/PARA armor types are attainable in the Season 1: Noble progression system. The knee guards are unique as the only set of knee guards that are colored according to the player's secondary armor color.
List of appearances