 Ramba uchiverenga ndima iyi - Pakutanga kweHondo Yenyika Yose, McCook akagadzwa kuva mukuru mukuru we1st Ohio Infantry muna April 1861. Akashumira mumidziyo yokuWashington uye akaona chiito paHondo Yokutanga yeBull Run. Musi waSeptember 3, 1861, akasimudzirwa kuva brigadier general wevanozvipira uye akatungamirira boka muTennessee. Akawana chinzvimbo chetezvara mukuru muuto renguva dzose nokuda kwechikamu chake mukutora Nashville, Tennessee. McCook akabva atungamirira 2nd Division muHondo yeOhio paHondo yeShiro pazuva rechipiri rekurwa, uyezve mumushandirapamwe wakazotevera kurwisa Korinde. Akakwidziridzwa kuva mukuru mukuru wevazvipiri musi waJuly 17, 1862. 