Whakaotihia te rerenga e whai ake nei: I te pakarutanga o te Pakanga Whenua o Amerika, ka uru atu a Jones ki te Ope Taua o te Kotahitanga. I te Hōngongoi 7, 1861, i uru ia ki te 37th New York Volunteers, e mohiotia whanuitia ana ko nga "Irish Rifles", i raro i a Colonel John H. McCunn. I te timatanga he tangata noa ia engari i kitea e ia i whiriwhiria ia ki te taumata o te tuarua tuarua e nga tangata i roto i te ope. I tae ia ki te Pakanga Tuatahi o Bull Run, e rua wiki noa i muri i tana whakaurunga, engari kaore i kite i tetahi mahi i te mea i puritia te waahanga. I whakaatuhia e Jones "te whanonga maia" i roto i ona tau tuatahi ki te ope, a, i te 4 o Noema 1861, ka eke ia ki te taumata tuatahi me te kaitiaki i te marama o Hanuere 21, 1862. I uru atu ia me nga "Irish Rifles" ki te III Corps a General Samuel P. Heintzelman, hei waahanga o te 3rd Brigade o te 3rd Division i raro i a Brigadier General Philip Kearny, i te pakanga o te Peninsula me te whai waahi ki Williamsburg,
E whitu nga Pines me te pakanga o nga Ra e whitu. I tae atu hoki a Jones ki te 37th New York Volunteers, i whakauruhia ki te 3rd Brigade o te 1st Division o te III Corps, i te Pakanga Tuarua o Bull Run. I te marama o Mei me te Pipiri, ka timata ia ki te mamae i te mate pukupuku, ka tukuna ki te hohipera i Washington, D.C. i te Mahuru 26 ka noho ki reira tae noa ki te mutunga o Oketopa. I noho hoki ia hei rangatira mo te Major General Franz Sigel i mua i te reti o te General Ambrose Burnside me te whakahoutanga o te Army of the Potomac.