From Halopedia, the Halo wiki
The HUL was designed for acquisition of military intelligence, and is required for personnel employing the Recon or Pilot helmets while on sensitive operations. When used in conjunction with the Command Network Module, it is a favorite of pathfinder units employing the AIR ASSAULT-class Mjolnir helmet. The device is often integrated with remote sensors into a hardened uplink/remote sensor package.
The HUL has been observed to be compatible with the following helmets:
The HUL has three observed variants, each with its own distinct physical appearance.
The standard HUL variant resembles a cube, and can be worn on either side of the helmet. Its adoption is reserved for personnel employing the Recon helmet during sensitive operations.
The modularity of the MJOLNIR armor has made it possible to attach multiple modules on the helmet. In cases where a HUL and a CNM and are both employed, the configurations are designated "FC", "FC-I", and "FC-I" depending on the variants used. FC refers to the configuration in which an external HUL and the "tall" CNM variant are both attached to the helmet. FC-I refers to the configuration in which an external HUL, along with the CNM-I, are integrated on the "camera" CNM variant, though this configuration has only been observed on the MJOLNIR/AA variant. FC-I refers to the configuration in which both the HUL and "tall" CNM are attached to the helmet.
The HUL and its variants serve as cosmetics and have no impact on gameplay.
All three variants of the HUL are available as attachments on several helmets in the armor permutations of Halo: Reach. The device is priced at different levels of Credits, depending on the base helmets. In Halo: The Master Chief Collection, the same HUL-attached helmets are unlockable in Season 1: Noble.
List of appearances