The Doniphon assault occurred as part of the Kwymar Suppressions during 17 BBY. The Galactic Empire triumphed over the Rebel forces stationed on Doniphon.
During 17 BBY, Imperial forces launched an offensive against Rebel outposts in the Kwymar sector, a military action remembered as the Kwymar Suppressions. Doniphon was among the planets targeted in this campaign.
During the engagement, numerous stormtroopers found themselves under fire from Rebel starfighters. Among the officers who sustained injuries was Sergeant Major Beilert Valance, whose platoon suffered a direct hit from a proton torpedo. Despite these significant losses, Imperial forces ultimately secured victory.
In the aftermath of the battle, Beilert Valance, severely wounded, was abandoned at Anglebay Station on Telos IV. Medical personnel there managed to save his life, but only through the extensive replacement of his organic components with cybernetics.
Years later, Beilert Valance, having become a bounty hunter, attacked and obliterated Anglebay Station, seeking to eliminate all evidence of his transformation.
The planet where Valance suffered his injury in Star Wars (1977) 16 was retroactively established as Doniphon by Jason Fry in the miniature scenarios titled The Hunt Within: Valance's Tale. Fry chose the planet's name as a tribute to Tom Doniphon, the character portrayed by John Wayne in the 1962 western film The Man Who Shot Liberty Valance.
In The Essential Guide to Warfare Author's Cut, Valance describes the opposing fighters as "Split-wings. ARC-170s, maybe. Or some kind of Z-95. HUD never painted them with a positive ID." This is probably an effort to bring the depiction of X-Wings in the battle into agreement with later materials that state X-Wings were not created until around 1 BBY.