Kammala jumla mai zuwa: A 1862, Sladen ya shiga rundunar sojojin Union don yakin basasar Amurka, ya shiga cikin kamfanin A, 33rd Massachusetts Infantry Regiment. Ya shiga cikin wasu daga cikin rikice-rikice na rundunar, ciki har da yakin Chancellorsville da yakin Gettysburg. Sladen ya shiga cikin Mayu 13-15, 1864
Yaƙin Resaca. Yayin da yake aiki a matsayin ma'aikaci a hedkwatar rundunar, Sladen ya bar mukaminsa don shiga yakin da son rai. Misalinsa na musamman ya karfafa abokansa a wani lokaci mai mahimmanci a cikin gwagwarmaya, kuma sun taru don kayar da abokan adawar su. A shekara ta 1895, ya sami lambar yabo ta girmamawa a cikin girmamawa ga jaruntakarsa na yakin basasa.