Kammala jumla mai zuwa: Shaw ya shiga cikin rundunar soja don yakin basasar Amurka, ya shiga kamfanin A, 35th New York Volunteer Infantry Regiment a matsayin mai zaman kansa a watan Yuni 1861. Daga bisani an ci gaba da shi zuwa ga dan jarida, kuma ya yi aiki har sai an cire shi tare da sauran rundunarsa a watan Yunin 1863. Shaw ya shiga cikin ayyukan rundunar a Virginia da Maryland, ciki har da; gina Fort Tillinghast da Fort Craig (kaka 1861); tsaro da sintiri a cikin da kewaye da Falls Church, Virginia (hunturu 1861-1862); tsaro da sintiri a cikin da kewaye da Falmouth, Virginia (spring 1862); fadace-fadace a tashar Rappahannock, White Sulphur Springs, da Gainesville (bazara 1862); Yaƙin Bull Run na biyu (Agusta 1862);
Chantilly (Satumba 1862); Kudancin Mountain (Satumba 1862); Antietam (Satumba 1862); da kuma Fredericksburg (Disamba 1862). A watan Janairu, 1863, an sanya rundunar zuwa brigade na tsaro a Falmouth, kuma ta yi tsaro da kuma aikin tsaro a kan hanyar jirgin ruwa na Aquia Creek. A watan Mayu, rundunar ta bar Maryland zuwa New York don a iya tattara shi.