Kammala jumla mai zuwa: Carl ya shiga cikin Kamfanin F na 4th Wisconsin Infantry Regiment (National Guard) a watan Afrilu 1896 kuma ya ba da kansa don yin aiki a cikin Yakin Spain-American a 1898. Brosius ya yi aiki a Kamfanin M na 1st Wisconsin Infantry Regiment a lokacin yakin, kuma an sake shi a watan Agustan 1900. A watan Yuli 1913, ya sake shiga cikin Kamfanin D na 1st Wisconsin Infantry Regiment; an canja shi zuwa Kamfanin F a watan Afrilu 1915 kuma an ci gaba da zama na biyu a watan biyu bayan haka. An tattara Brosius a cikin sabis don
Yakin kan iyakar Mexico a watan Yunin 1916, inda ya umurci rundunar soji. Bayan da ya sami kyakkyawan suna a matsayin mai horar da jiki, Brosius ya kasance a cikin Amurka a lokacin yakin duniya na, yana tafiya daga sansani zuwa sansani don aiwatar da shirye-shiryen horo ga sojojin Amurka.