Rubuta ci gaba ga wannan sakin layi - A lokacin da aka fara yakin Spain da Amurka, Upton ya shiga rundunar sojojin Amurka. Ya yi aiki a matsayin mai zaman kansa a Kamfanin H na 2nd Oregon Volunteer Infantry Regiment kuma ya shiga cikin kamawar Guam da kuma yakin basasa na Philippines.
Ka yi haƙuri. Upton ya kasance a cikin Oregon National Guard bayan yakin. A shekara ta 1911, ya yi aiki a matsayin babban jami'in soja na 3rd Regiment na Oregon Infantry.