Whakaotihia te rerenga e whai ake nei: I te tīmatanga o te Pakanga ā-Iwi o Amerika i te tau 1861, ka tū a Fesler ki te taha o te Uniana. I te Akuhata 30, 1861, i uru ia ki te Ope Taua o te Uniana i Morgantown, Indiana. I whakawhiwhia a Fesler ki te Kapene o te Kamupene G i te 27th Indiana Infantry Regiment. I whakahau a Fesler i tana kamupene i te
Ko te Pakanga Tuatahi o Winchester me te Pakanga o Cedar Mountain. I te tau 1862, i whakawhiwhia a Fesler's Regiment ki te 12th Army Corps, i reira ka noho tonu i te tau 1863. I whakahau a Fesler i tana kamupene i te Pakanga o Antietam, tata ki Sharpsburg, Maryland, i te Mahuru 17, 1862. I noho tana rerenga i te hotoke o te tau 1862 ki te 1863 i te puni i Stafford Courthouse, Virginia, a i te Hui-tanguru 13, 1863, i whakatairangahia a Fesler hei Lieutenant Colonel o te 27th Indiana. I te Poutu-te-rangi 1863, ko te 12th Corps, ko te 27th Indiana tetahi waahanga, i tukuna he whetu hei tohu mo tana roopu. I te Mei 5, 1863, i whara a Fesler i te pakanga i Chancellorsville, i Spotsylvania County, Virginia. I muri mai ka whakahau ia i te 27th Indiana mai i te Hōngongoi 2-3, 1863 i te Pakanga o Gettysburg i te wa i whakanohoia ai te koronel o te rerenga ki te rangatira o tana pereti. I whai waahi a Fesler me tana ope ki te whakakore i nga tutu a New York City Draft i muri mai i taua marama.