I mahi ia i te Pakanga o Mexico-Amerika me te Major James Duncan's Battery A, 2nd U.S. Artillery, i reira ia i whakawhiwhia ai i nga wa katoa mo "nga kounga pai" mai i te taumata o te tangata takitahi i te 1845 na te taumata o te tuarua tuarua i te Pipiri 28, 1848, i muri mai ka noho tonu i muri i te pakanga i te Hanuere 26, 1849. I noho a Benson ki te Pūhiko A i ngā pakanga o Palo Alto
Ko Resaca de la Palma, ko Monterrey, ko Vera Cruz, ko Churubusco. I eke ia ki te tūranga o te kaitiaki tuatahi i roto i te whakahau o te pupuhi pupuhi i roto i te papahiko a Duncan i raro i te rangatira o te wehenga a Lieutenant Henry Jackson Hunt i te whakapae o Mexico City, he tino kaha i te Pakanga o Chapultepec i te San Cosmé Garita.