Rubuta ci gaba ga wannan sakin layi - Bayan faduwar Vicksburg, an tura rukunin Osterhaus zuwa Tennessee. A cikin Kamfen na Chattanooga ya taimaka wa Manjo Janar Joseph Hooker a kama Dutsen Lookout. Osterhaus sa'an nan kuma ya shiga cikin Atlanta Campaign amma rashin lafiya na tsawon wata daya ya sa ya rasa yakin basasa na Atlanta.
Ka yi haƙuri. Duk da haka, ya koma umurnin kuma ya taka muhimmiyar rawa a yakin Jonesborough. Bayan kama Atlanta, ya karbi umurnin XV Corps, daya daga cikin rundunonin hudu da aka hada sojojin, a cikin Sherman's March zuwa Sea. A watan Maris na shekara ta 1865, an nada Osterhaus a matsayin shugaban ma'aikata a cikin Rundunar Sojoji na Yammacin Mississippi a karkashin jagorancin Maj. Janar Edward Canby, kwamandan da ba shi da kwarewa a cikin babban kwamandan. Osterhaus ya bauta wa Canby ta hanyar yaƙe-yaƙe na Spanish Fort da Fort Blakely. Lokacin da Edmund Kirby Smith ya ba da sojojin Confederate a cikin Trans-Mississippi Theater, an aika Osterhaus a matsayin wakilin Canby kuma saboda haka ya sanya hannu kan takardun a madadin sojojin Union.