Ya yi aiki a sansanin soja a Savannah, Georgia a matsayin mataimakin mataimakin na uku na Artillery har zuwa 1846, lokacin da aka nada shi don sabis na tarawa. An ci gaba da shi a ranar 18 ga Yuni, 1846, kuma ya shiga cikin yakin Mexican-American; ya kasance a Tampico da
Vera Cruz. - Ta yaya za ka yi haka? Beckwith ya shiga cikin binciken Railway Railway daga 1853 zuwa 1857 tare da John Williams Gunnison. Musamman, Jirgin Ruwa na Farko na Farko ya bi hanyar da ya ba da shawarar. Rahotonsa, wanda ya haɗa da bincike mai zurfi na Great Salt Lake, yana ɗauke da "bayani da yawa game da tsire-tsire, dabbobi, yanayi, da kuma yanayin ƙasashen da ya bincika". Ya yi nasara da Gunnison a matsayin jagoran binciken bayan mutuwarsa, kuma da kansa ya ba da shawarar hanyar jirgin kasa. Ya kuma shiga cikin gina hanyoyi na soja a Nebraska da Kansas, tsakanin 1857 <unk> 1859.