Kammala jumla mai zuwa: An tura Simpson zuwa 2nd Battalion, Royal Australian Regiment a watan Janairun 1954, inda aka daukaka shi zuwa Sgt a 1955, yana aiki a
Malaya daga Oktoba 1955 na shekaru biyu masu zuwa. Daga baya aka tura shi zuwa Kamfanin Sabis na Musamman na 1 (SAS) a watan Nuwamba 1957 kuma ya yi aiki tare da wannan rukunin har sai an zaɓe shi a matsayin ɗaya daga cikin membobin rukunin farko na Kungiyar Horar da Sojojin Australiya ta Vietnam (AATTV) da aka aika don taimakawa sojojin Kudancin Vietnam a watan Yulin 1962. Bayan shekara guda, ya koma SAS a Ostiraliya kuma ya yi aiki a can na watanni goma sha biyu masu zuwa.