By the late 1960s Killen had somewhat moderated his views, and in the government of John Gorton he served as Minister for the Navy from 1969 to 1971. When William McMahon became Prime Minister, Killen was dropped from the Ministry. 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. He served as Minister for Defence in the Fraser Government from 1975 to 1982.