Rubuta ci gaba don wannan sakin layi - Da yake son bin sawun mahaifinsa, Johnson ya sami izini daga Janar Enoch Crowder don halartar Jami'ar California (a Berkeley) inda ya sami digiri na farko na Arts (tare da girmamawa) a 1915 da Juris Doctor a 1916 (ya ninka darussan don kammala karatu a cikin rabin lokacin da ake buƙata). An canja shi zuwa Kotun Shari'a ta Janar (JAG), daga Mayu zuwa Oktoba 1916 ya yi aiki a karkashin Janar John J. Pershing a Mexico tare da Pancho Villa Expedition
An ci gaba da kyaftin din a ranar 1 ga Yuli, 1916, an canja shi zuwa hedkwatar JAG a Washington, DC, a watan Oktoba 1916. An ci gaba da shi zuwa babban jami'in a ranar 15 ga Mayu, 1917, kuma zuwa laftanar Kanar a ranar 5 ga Agusta, 1917. An kira shi Mataimakin Babban Jami'in Janar a watan Oktoba 1917, kuma a wannan watan ne aka kira shi zuwa kwamiti na Ma'aikatar War a kan horar da sojoji (Amurka ta shiga yakin duniya na ranar 6 ga Afrilu, 1917).