Considered in this chapter are the psychological requirements for flight in terms of the intelligence and aptitude testing carried out by the Aptitude Test Section. Due to the lack of resources and expertise in South Africa at the outbreak of the War, priority in intelligence testing was given to the most modern branch of the UDF, the South African Air Force. Considered briefly here are the origins of intelligence testing and its prewar use in South Africa where there were attempts to distinguish and account for differences between black and white children and determine the aptitude of workers. As such, intelligence and aptitude testing were associated with the rational and scientific means of creating a modern country in terms of industry and, during the War, its military. Yet, despite the scientific methods of testing, assumptions of capability were underpinned by moral notions of courage and character stemming from the First World War. Aptitude testing was the method of “weeding out” those most likely to be overcome from fear – and who were believed to lack the necessary moral fibre for combat. This chapter then discusses the work of the ATS in their attempt to determine the ideal aviator, looking at the testing process in terms of the development of tests, the methods used to determine measurable attributes such as intelligence as well as more intangible qualities such as “temperament” and “personality.” It argues that, despite the scientific basis of testing, there existed an ambivalence related to what constituted an ideal temperament. This took on moral connotations that served to subordinate the needs of the individual to the wellbeing of the group.