Kammala wannan jumla: Sanderson ya shiga aikin soja a cikin Rundunar Sojojin Amurka ta 15 a ranar 24 ga Oktoba, 1861. Mahaifinsa John P. Sanderson ya riga ya kasance mai kula da wannan rundunar da ke aiki daga ranar 14 ga Mayu, 1861 har zuwa ranar 4 ga Yuli, 1863. An ba shi izini na biyu a ranar 31 ga Oktoba, 1861. Ya karbi takardar shaidar a matsayin 1st Lieutenant a ranar 7 ga Afrilu, 1862, don aikin jaruntaka da kuma daraja a cikin
Yaƙin Shiloh Tennessee. An ci gaba da shi zuwa 1st Lieutenant a Regular Army a ranar 9 ga Nuwamba, 1862. Sanderson ya karbi takardar shaidar ta biyu a matsayin kyaftin a ranar 1 ga Satumba, 1864, don aikin jaruntaka da kuma aiki mai kyau a lokacin Atlanta Campaign.