During the Damocles Gulf Crusade, a large number of Imperial Guard Soldiers surrendered or were captured by the Tau Military. Many more were abandoned during the Imperial withdrawal and captured, as well. Rather than exterminating these soldiers, the Tau Commander Farsight offered them the option to stay imprisoned or to join Tau Society and embrace their role serving the Greater Good. Many chose the latter, settling on Tau worlds and serving the Tau Empire as soldiers, a tradition that their descendants kept up. These forces later increased in size and number after the Tau conquered several human inhabited worlds on the fringes of Imperial space in later Phase Expansions of the Empire and as Guard Forces surrendered to the Tau Empire during numerous small-scale skirmishes between the Tau and the Imperium.
Gue'vesa soldiers are very much like their Imperial Guard counterparts in terms of training and mostly use the same armaments. Most Gue'vesa are armed with lasguns and use vehicles including Sentinel Walkers produced by Imperial industrial facilities set up in Tau Space during the Damocles Crusade. However, they have access to superior Tau body armor, and a few Gue'vesa soldiers have been equipped with Tau pulse weaponry, a few vehicles are equipped with Tau weapon systems.