Kammala jumla mai zuwa: A 1915 digiri na biyu na Royal Military College, Sandhurst, Dempsey aka yi umurni a matsayin na biyu Lieutenant a Royal Berkshire Regiment. A matsayinsa na ƙaramin jami'i, ya yi yaƙi a Yammacin Yammacin lokacin Yaƙin Duniya na Farko, inda aka ji masa rauni, kuma an ba shi lambar yabo ta Soja. Bayan yakin ya yi aiki a Iraki a lokacin
Rikicin Iraki na 1920, Iran a lokacin yakin basasa na Rasha, da kuma Indiya.