Military historians have debated the role of the War Office Selection Board (WOSB) in creating a “People’s Army” and democratising the British military during the Second World War. The role of these boards in reconfiguring the identity of the psychiatrist and the boundaries of their expertise in mid-twentieth century Britain, however, has been largely overlooked. This paper examines the WOSB as a boundary object, which could be read as a democratising force, a treatment for a “sick” organisation, a set of scientific (and not so scientific) practices, or a technology for increasing the flow of officer candidates and the image of the army whose underlying principles were irrelevant. It examines the contexts that motivated actors to opt for these categorizations, and traces how the dominant narrative changed over time, whilst analysing the lingering aspects of categorizations and what proved particularly useful or problematic about these associations in the given context.