He enlisted for service in the Royal Australian Air Force during World War II; he was discharged in 1945 with the rank of flight sergeant.

[4] He quickly became known as a talented orator but his outspokenness and commitment to causes that Menzies regarded as contrary to Liberal Party principles limited his chances of promotion.

", and that story was widely repeated for many years, but he later confessed he had made it up for the Courier-Mail to overcome his disappointment at not, in fact, receiving such a call from Menzies.

After the Liberals lost office to Labor under Gough Whitlam, he served in the Shadow Cabinet under Billy Snedden and Malcolm Fraser from 1972 to 1975, acting as the party spokesman on Education and later Defence.

[4] During this time he oversaw a major review of the Australian Defence Force and also the military build-up which followed the Soviet invasion of Afghanistan in 1979.

[9] Killen had a reputation as a great parliamentary wit who developed close friendships with many people on both sides of politics, among them Gough Whitlam, Fred Daly and Barry Cohen.

[5] In 1976, Mungo MacCallum published an article in the Nation Review magazine alleging that Killen was having an extramarital affair with Margaret Guilfoyle, one of his cabinet colleagues.