[1] Having served in the cadets as a youth, following his 18th birthday, Whitelaw enlisted in the Militia – Australia's part-time military force – on 11 June 1939.
Based on his abilities and education, he was appointed provisionally as a lieutenant on 15 March 1940, and subsequently undertook full-time duty from 1 May 1940 to 25 September 1941, when he transferred to the Second Australian Imperial Force (2nd AIF).
Promoted to captain, he was wounded in action on Bougainville; however, he remained on duty and subsequently earned a mention in despatches on 6 June 1945 while serving as an artillery forward observer during an amphibious assault at Porton Plantation to cut off the withdrawing Japanese.
[5] In 1955, Whitelaw, then a major, moved with his wife, Nancy and their three young daughters to the Canadian Staff College at Kingston.
[5] Promoted to colonel in 1970, Whitelaw was appointed the Chief of Staff at Headquarters Australian Army Forces Vietnam.
For his achievements in this role he was later appointed a Commander of the Order of the British Empire in September 1971,[6] and awarded the United States Bronze Star Medal.
In 1977, Whitelaw assumed the position of Deputy Chief of the General Staff (DCGS) and in June that year was appointed as an Officer of the Order of Australia.