Kammala jumla mai zuwa: Bayan shekaru shida a cikin ajiyar sojojin tare da Australian Light Horse, Green ya shiga soja a lokacin da yakin duniya na farko ya barke kuma ya shiga matsayin laftanan a cikin Rundunar Sojan Ruwa ta 6 a kan "Suevic" a ranar 21 ga Disamba, 1914. Ya ga aiki a Misira, a yakin Gallipoli da kuma Yammacin Yamma; an harbe shi sau ɗaya a Gallipoli, ya dawo tare da dogon asibiti kuma ya koma Australia a 1916, kafin ya sake shiga cikin watan Nuwamba 1916. Ya yi aiki har sai da aka sake ji rauni lokacin da ya rasa kafa a
Yaƙin Menin Road a Belgium, a watan Satumbar 1917. Ya koma Ostiraliya a ranar 30 ga Yuni 1918 kuma ya koma gonarsa a Woolomin. Ya kasance mai haɗin gwiwa kuma mataimakin shugaban farko na Limbless da Maimed Soldiers 'Association, memba na Kwamitin Kare Tsaro na Tamworth, kuma ya kasance dan takarar Jam'iyyar Progressive wanda bai yi nasara ba a zaben jihar na 1922.