During the Damocles Gulf Crusade, a large number of Imperial Guard Soldiers surrendered or were captured by the Tau Military. Many more were Abanndoned during the Imperial Withdrwal and captured as well. Rather than exterminating these soldiers, the Tau Commander Farsight offered them the option to stay imprisoned or join into Tau Society and embrace there role serving the Greater Good. Many of which chose the latter, settling on Tau Worlds and serving the Tau Empire as soldiers, a tradition which there desendants kept up. These forces were latter increased in size and number after the Tau conquered several human inhabited worlds on the fringes of Imperial space in latter Phase Expansions of the Empire and as Guard Forces which 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 as well as using vehicles including Sentinal Walkers produced by Imperial Industrial facillities set up in Tau Space durring the Damocles Crusade. However, they have access to superior Tau body armor and a few Gue'vesa soldiers have been equiped with Tau Pulse weaponry, as well as equiping a few vehicles with Tau Weapon systems.