Mezue ahịrịokwu na-esonụ: Williamson gbakere n'oge iji soro na Vicksburg Campaign na Siege nke Vicksburg na-esote. Mgbe ọdịda nke obodo ahụ, o weere iwu nke 3rd Brigade, 1st Division, XV Corps ruo Septemba, 1863 wee nye iwu nke 2nd Brigade, 1st Division, XV Corps na Agha nke Chattanooga. E tinyere nkewa Williamson, nke Peter J. Osterhaus duziri na nkewa nke Joseph Hooker ma sonye na
Agha nke Ugwu Lookout. E weghachiri ngalaba ahụ na ndị agha nke Tennessee na Williamson duru Brigade nke abụọ n'oge Atlanta Campaign. N'agha a lụrụ na Jonesborough, e merụrụ ya ahụ́ n'aka. Na Disemba 19, 1864 ọ natara nkwalite brevet na brigadier general nke ndị ọrụ afọ ofufo US, na Jenụwarị 13, 1865 nkwalite zuru oke na brigadier general na Machị 13, 1865 nkwalite brevet na isi ndị ọrụ afọ ofufo. N'oge okpomọkụ nke afọ 1865 ọ nyere iwu na District nke St. Louis ma wepụ ya n'ọrụ afọ ofufo na August 24, 1865, mana ọ nọ na njem nlegharị anya nke ndị agha na West ma ọ chọpụtabeghị ruo mgbe ọ laghachiri na Ọktoba 1865.