Kammala wannan jumla: A shekara ta 1861, Irwin ya ba da rahoto don aiki a kan jirgin ruwa na jirgin ruwa. Yaƙin basasa na Amurka ya ɓarke a watan Afrilu na shekara ta 1861, kuma Irwin ya ga babban aiki a kan sojojin Confederate a kan "Wabash". A lokacin yawon shakatawa na Irwin, "Wabash" ya shiga cikin
kama Fort Hatteras da Clark a Hatteras Inlet, North Carolina, a ranar 29 ga Agusta, 1861, kafin ya zama babban jirgin ruwa na Kudancin Atlantic Blockading Squadron, daya daga cikin rundunonin da ke aiki a cikin toshewar Union na tashar jiragen ruwa na Confederate. "Wabash" sannan ya shiga cikin kama Fort Walker, Fort Beauregard, da Port Royal Sound, South Carolina, a cikin yakin Port Royal a ranar 7 ga Nuwamba 1861. Irwin daga baya ya kasance a cikin umurnin jirgin ruwan howitzers "Wabash" da aka sanya a bakin teku a lokacin yakin Port Royal Ferry, South Carolina, a ranar 1 ga Janairu, 1862, kuma yana cikin jirgin "Wabash" don yakin Fort Pulaski a Cockspur Island, Georgia, a ranar 10 zuwa 11 ga Afrilu, 1862. An ci gaba da shi zuwa kwamandan kwamandan a ranar 16 ga Yuli 1862.