Whakaotihia te rerenga e whai ake nei: I ora a Williamson i te wa ki te whai waahi ki te Campaign Vicksburg me te Siege o Vicksburg e whai ake nei. Whai muri i te hinganga o te taone nui, i riro ia ia te rangatira o te 3rd Brigade, 1st Division, XV Corps tae noa ki te Mahuru, 1863 ka whakahau ia i te 2nd Brigade, 1st Division, XV Corps i te Pakanga o Chattanooga. Ko te wehenga a Williamson, i whakahaua e Peter J. Osterhaus i whakauruhia mo te wa poto ki nga ope i raro i a Joseph Hooker ka uru ki te
Te Pakanga o te Maunga Tirohanga. I whakahokia te wehenga ki te Army o te Tennessee a ko Williamson te rangatira o te 2nd Brigade i te pakanga o Atlanta. I te Pakanga o Jonesborough i whara ia ki te ringa. I te Tihema 19, 1864 i whakawhiwhia ki a ia he whakatairanga i te brevet ki te brigadier general o nga U.S. Volunteers, i te Hanuere 13, 1865 he whakatairanga katoa ki te brigadier general me te Maehe 13, 1865 he whakatairanga i te brevet ki te rangatira nui o nga kaitautoko. He poto i te raumati o te tau 1865 i whakahau ia i te rohe o St. Louis, a, i whakauruhia mai i te ratonga mo te kore i te 24 o Akuhata 1865, engari i te haerenga tirotiro o nga pou ope i te Hauauru, a kaore i kitea tae noa ki tana hokinga mai i te Oketopa 1865.