conflict. In October 1936, King Leopold III announced that Belgium would remain neutral in the event of another war in Europe as part of what he termed an Independent Policy (Politique d'Indépendance). To this end, the Belgian government tried to steer a path away from alliances: leaving the Locarno Treaty, repudiating a defence pact with France signed in 1920 and receiving a guarantee of neutrality from Nazi Germany in 1937. During this period, the Belgian military was reorganized as an exclusively defensive force and began construction and modernization of fortifications around the country, particularly around Liège Province near the German border. On the declaration of war between the United Kingdom, France, and Germany in September 1939, the Belgian government launched a crash re-armament program, augmenting the national defenses by creating the K-W Line linking the National Redoubt at Antwerp with the south along the River Dijle, just behind the main Fortified Position of Liège. 18 Days' Campaign With the German invasion of Poland in September 1939, although still following a policy of neutrality, the Belgian government began general mobilization. By 1940, the army numbered between 600,000 and 650,000 men (nearly 20 percent of the male population of Belgium) making it approximately four times larger than the British Expeditionary Force and twice as large as the Dutch army at the time. The invasion of Belgium by Nazi Germany started on May 10, 1940, under the codename Fall Gelb ("Case Yellow") as part of the wider invasion of France, the Netherlands and Luxembourg. The Belgian Albert Canal fortifications, some of the most modern defensive networks in Europe, proved almost useless. At Eben-Emael, the fort held by 1,200 Belgians was taken when the Germans deployed 500 glider-borne Fallschirmjäger against them, opening the border for Blitzkrieg-style warfare. Almost all of the air force's modern Hurricane fighters were also destroyed by the Luftwaffe on the ground at Schaffen airfield on May 10. The German breakthrough at Sedan, which had been thought impassable, meant that defenders of the K-W Line risked being outflanked, and had to withdraw on 16 May. The German invasion triggered a panic amongst Belgian civilians in the path of the advancing German army. By 11 May, the roads leading westwards, away from the fighting, were blocked by refugees, hampering the eastward advance of French and British forces. It is estimated that around two million civilians fled their homes during the campaign. The