ɪn wˈʌn θˈaʊzənd ˈeɪthˈʌndɹɪd nˈaɪnti ˈeɪt, dʒˈɑːnstən ɛnlˈɪstᵻd ɪnðə juːnˈaɪɾᵻd stˈeɪts ˈɑːɹmi tə fˈaɪt ɪnðə spˈænɪʃ ɐmˈɛɹɪkən wˈɔːɹ, sˈɜːvɪŋ ɪn kjˈuːbə wɪððə fˈɜːst jˈuː.ˈɛs. vˌɑːləntˈɪɹ kˈævəlɹi ɹˈɛdʒɪmənt, bˈɛɾɚ nˈoʊn æz ðə ɹˈʌf ɹˈaɪdɚz.
In 1898, Johnston enlisted in the United States Army to fight in the Spanish–American War, serving in Cuba with the 1st U.S. Volunteer Cavalry Regiment, better known as the Rough Riders.