This thesis examines the reasons why Stalin purged his Red Army during 1937-38 at the same time as World War was looming. This gutting of the officer corps created huge turmoil inside the Red Army and affected at the very least 35,000 army leaders, resulting in thousands of discharges, arrests and executions. Previous explanations of the military purge have typically concentrated on Stalin’s relationship with his military elite and how he supposedly believed they would become a block to his expanding power. Framed as the ‘Tukhachevskii Affair’, after its most famous victim, the military purge is most commonly depicted as merely the extension of Stalin’s advancing lust for total power into the Red Army. This thesis will show that such accounts are unsupported and inadequate and will provide a new explanation of the military purge. This thesis will show that Stalin did not attack his army elite in order to increase his power, but this was a last minute action made from a position of weakness. Taking the formation of the Red Army in early 1918 as its starting point, this thesis will argue that the key to understanding Stalin’s attack on the officer corps in 1937 is to understand how the military was perceived as susceptible to subversion. From its very formation the Red Army was seen as a target of ‘enemies’, ‘counterrevolutionaries’ and was regarded as vulnerable to infiltration. Over a period of twenty years the army faced an array of exaggerated and imaginary threats. Stalin was plagued by nagging doubts about the reliability of his forces, from mass instability in the lower ranks to supposed disloyalty in the military elite. By 1937 these perceived threats had culimated in a spy scare and it was this that finally forced Stalin to crack down on the Red Army.