Rubuta ci gaba ga wannan sakin layi - 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 cikin rikici na 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.