Mezue ahịrịokwu na-esonụ: N'ịchọ ịgbaso nzọụkwụ nna ya, Johnson nwetara ikike site n'aka General Enoch Crowder ịga Mahadum California (na Berkeley) ebe ọ natara akara ugo mmụta Bachelor of Arts (nke nwere nsọpụrụ) na 1915 na Juris Doctor na 1916 (na-agbakwunye okpukpu abụọ na ọmụmụ iji gụsịrị akwụkwọ na ọkara oge achọrọ). N'ịgafe na Judge Advocate General's Corps (JAG), site na Mee ruo Ọktọba 1916 o jere ozi n'okpuru General John J. Pershing na Mexico na ndị otu
Pancho Villa Expedition. e buliri ya n'ọkwa onye isi na July 1, 1916, a kpọfere ya n'isi ụlọ ọrụ JAG na Washington, D.C., n'October 1916. E buliri ya n'ọkwa onye isi n'ụbọchị 15 nke ọnwa Mee, afọ 1917, e buliri ya n'ọkwa lieutenant colonel n'ụbọchị 5 nke ọnwa Ọgọstụ, afọ 1917. A họpụtara ya osote Provost Marshal General n'ọnwa Ọktoba 1917, na otu ọnwa ahụ ka a họpụtara ya na ngalaba ngalaba agha na ọzụzụ ndị agha (US abanyela Agha Worldwa Mbụ na Eprel 6, 1917).