Ka kammala wannan magana: Sa'ad da Yaƙin Duniya na Biyu ya ɓarke, McKinnon yana Ingila a kan wani horo na horo. Ya shiga Rundunar Sojoji ta New Zealand ta biyu kuma ya yi aiki tare da Rukunin New Zealand na 3 a lokacin
yaƙin neman zaɓe a tsibirin Solomon. Da farko ya kasance kwamandan rundunar sojan sama ta 28 mai nauyi amma lokacin da aka rushe rundunarsa a watan Yulin 1942 ya karbi rundunar sojan sama ta 29 mai haske. Tare da rundunarsa, ya sauka a kan Treasury da Green Islands. Lokacin da aka cire rukunin a cikin 1944, ya koma Ingila don halartar Kwalejin Ma'aikata a Camberley. Bayan kammala karatunsa na ma'aikata, ya shiga Rukunin 2 na New Zealand, a lokacin yana yaƙi a Italiya tare da Sojoji na Takwas, tare da sauran jami'an bindiga waɗanda suka yi aiki a cikin Pacific. Da ya isa Italiya a watan Fabrairun 1945, ya kasance mataimakin kwamandan farko na 4th Field Regiment sannan kuma na 6th Field Regiment.