Kammala jumla mai zuwa: A lokacin yakin basasa Osterhaus an nada shi babban jami'in Missouri Volunteer Infantry na biyu kuma a farkon shekarar yakin ya yi aiki a Missouri da Arkansas, inda ya dauki bangare a cikin yakin Wilson's Creek da kuma yakin Pea Ridge. A Pea Ridge ya umurci sojojin da suka fara hulɗa da sojojin Confederate da ke ci gaba a hagu na Union. An ci gaba da shi zuwa brigadier janar a ranar 9 ga Yuni, 1862. A 1863 ya umurci wani sashi a cikin
Yaƙin Port Gibson, inda ya nuna kwarewar da ya dace wajen yin amfani da masu kare kariya na Confederate daga matsayi mai kyau.