On the surface of Volkus, grav-chute troops from the Storm Aquila and the Tempestus Scions were locked in a sprawling melee with Vespid and Fire Caste battlesuit teams that had infiltrated the Hive City.
Several jump-pack assault squads from the Mordian Iron Guard were also helping in the fighting.
Unlike other troops that used grav-chutes, the Mordian Iron Guard were among the few Astra Militarum forces that formed jump-pack assault squads.
Such equipment required extensive training and was expensive, and the mortal soldiers equipped with jump packs had to be the elite of the elite.
Yet even so many troops skilled in using flight equipment or antigravity Jump Devices could barely keep the numerous T'au infiltrators in check.
Vespid, the homeworld of the Vespid, was a gas giant. Its upper atmosphere held thousands upon thousands of floating rock islands suspended by gases lighter than air, and these islands were their homes.
Air pressure inside the islands varied greatly with altitude. All manner of strange, unique crystals lay at their bases, and only the larger female Vespid could reach the lowest levels to harvest them. These crystals formed the foundation of their technology.
These crystals also formed part of the strangely shaped weapons they used—the Neutron Blasters.
Negotiations between these indigenous Xenos and the Water Caste had yielded little success because their ways of thinking differed enormously. Eventually, however, guided by the Greater Good, the T'au came up with a solution.
They simply made a special helmet to serve as a communication device, using it to reach a crystal trade agreement with the Vespid.
Under the helmets' influence, these higher-ranking Vespid gradually accepted the Greater Good and eventually became loyal to the T'au Empire.
The subjugated Vespid formed "Stingwings" teams, participating in the T'au Empire's military operations as a mercenary species.