Between September 1939 and June 1940, the British Expeditionary Force confronted the German threat to France and Flanders with a confused mindset, an uncertain skills-set and an uncompetitive capability. The well-trodden campaign chronology does not do justice to the deep-seated origins of BEF performance, nor does it reveal the campaign's lasting impact on the British Army for the remainder of the war. This study of the command, control and communication systems uncovers how an absence of official guidance and a degree of discretion at every command level created multiple systems which were neither efficient in peacetime nor resilient in wartime. The BEF was made up of personnel with a vast array of experiences gained at imperial postings around the world and over a considerable time period; inevitably these diverse experiences caused variation in all areas of army life and policy. Throughout ,training and deployment" opportunities were missed to establish metric standards of capability and update operating procedures, not least because such topdown prescription was regarded as an infringement of an officer's discretion to command their subordinates as they saw fit. This left units dependent on their commander's energy and open-mindedness to new techniques as much as his experience and training. Peacetime had dangerously ingrained unique habits into many personnel, leaving officers and units deficient in self-awareness and the drive to improve upon satisfactory performance. The BEF was the product of decades of imperial policing, but also months of Phoney War; this unique prelude to combat left it paradoxically complacent about its own abilities and also unclear about the capability and combat tactics of the opponent it faced. It is against this background the campaign was fought and lost.