This article consists of fan-made material. It is not Canonical.
The Four Sword Campaign was a series of assaults that took place before and during the Third Sphere Expansion. It was composed of four notable Tau commanders, each with a distinct goal; Shas'Ar'O Li'Sun'yi was brought out of retirement to oversee the campaign south, forming the First Sword. Shas'O Bentu, an ageing veteran of countless wars, was dispatched to combat Ork and Imperial encroachment, forming the Second Sword. Shas'O Nan'cova was given the Third Sword taskforce, and instructed to root out and destroy an Eldar infestation. The Fourth Sword was supposed to be a campaign to the galactic east, but the title was ultimately given to Shas'O Shas'erra, commander of the Third Phase Expansion.
Although ultimately a success for the Tau Empire, the campaign met with considerable difficulty. The First Sword was halted after defeating a previously unknown alien race due to lack of momentum and depletion of its command structure. The Second Sword stormed through Ork space, claiming countless worlds, but was ultimately halted by an Imperial Crusade that inflicted heavily losses on its second line. Most Tau scholars consider the battle of 'Medusa V' to be the end of the Fourth Sword conflict.
The Third Sword is the most often documented taskforce of the Four Sword Campaign. O'Nan'cova was eventually joined by both O'Bentu and Ar'O'Sun'yi, who assisted him in his campaign against the Eldar Craftworld of Ko'shanniah.
During the battle, an ancient race known as the Necrons were located. The Eldar had been guarding their 'Tomb World' for centuries, and after their defeat the Necron threat was brought to light. Following the suicide of O'Sun'yi, it was discovered the Aun overseeing the campaign was, in fact, a Necron Lord disguised as a Tau. O'Nan'cova returned to the fray, leading his depleted forces into battle beside the Eldar. He entered the Necron Tomb and successfully destroyed it, though was killed in the process. His sacrifice marks the end of the Third Sword, and the Four Sword Campaign as a whole.
Despite several major losses, and some horrifying events, the Four Sword Campaign was overally a tremendous success for the Tau Empire.