While at Melbourne, he obtained a half-blue in rifle shooting, but did not complete his studies due to the outbreak of World War II.
[3] Kennison enlisted in the Second Australian Imperial Force (AIF) in 1939, and served as a gunner in Australia and the South West Pacific Area.
In December, the court-martial found Kennison not guilty of the charges of not keeping the camp in a proper state of cleanliness, and not maintaining discipline among the draft.
[5] He returned to Melbourne, where he spent ten years working in the retail sector, eventually managing the drapery and department store Hicks, Atkinson & Sons on Collins Street.
In 1956, Kennison was recruited to the Australian Secret Intelligence Service, having been offered the role in no small part due to his war record and investigative experience during the Morotai and Ambon trials.