Rubuta ci gaba don wannan sakin layi - Sneden ya bar Brooklyn a 1861 don shiga cikin New York Volunteer Infantry Regiment na 40, ko "Mozart Regiment", na Sojojin Potomac. Ya yi aiki a matsayin mai kula da lokacin da rundunarsa ta yi zango a kusa da Leesburg Turnpike. Farawa daga Janairu 12, 1862, Sneden ya yi aiki a kan ma'aikatan Samuel P. Heintzelman na III Corps, da farko, a matsayin mai zane a kan aikin taswira, daga baya, a matsayin injiniyan topographical. A ranar 22 ga Maris, 1862, Sneden ya shiga tare da Heintzelman don Kamfen na Peninsula, yana shiga cikin Yaƙin Williamsburg, Yaƙin Bakwai Bakwai, Yaƙin Savage's Station
, da kuma yakin Glendale. Komawa zuwa Arewacin Virginia, ya shiga cikin yakin na biyu na Bull Run. An ba shi izinin kare Washington, DC, da farko a Alexandria, Virginia, sa'an nan kuma a Arlington House.