Belgium mobilized its armed forces beginning on 25 August 1939. With the outbreak of the war, the government immediately reaffirmed the nation's neutrality, retaining the right to strengthen its military to prevent attack. Belgian King Leopold III acted as commander in chief of the armed forces, which consisted of an army of 18 infantry divisions, 2 partly motorized divisions, and 2 motorized cavalry divisions in May 1940. In all, the army numbered some 600,000 men. Although impressive on paper, the army suffered from serious weaknesses. Both its men and officers were poorly trained and equipped. Further, the army had virtually no antiaircraft artillery and only 54 tanks (42 British Carden-Loyd M1934s and 12 French Renault AMC-35s). The navy consisted of only a few small coastal defense vessels.
In hopes of remaining neutral, King Leopold had prevented significant military coordination with the French and British military staffs. Although British and French forces did come to the aid of Belgium when it was invaded by German forces on 10 May 1940, the Germans breached the initial Belgian defensive line along the Albert Canal that same day. King Leopold then withdrew the bulk of his forces to a line east of Brussels. British and French troops reinforced the new line, but the German strike through the Ardennes flanked it. Soon, the Allies were forced to abandon Brussels and the surrounding area.
By 24 May, the Belgian army had regrouped in western Flanders, where it was again supported by both French and British forces. The only major battle of the campaign occurred there, on 24–25 May, with Belgian forces again unable to hold off the superior German forces. On 28 May, King Leopold surrendered his army. In addressing the House of Commons on 4 June concerning the Belgian defeat, British Prime Minister Winston L. S. Churchill said that the surrender was given "suddenly, without prior consultation, with the least possible notice" and that this action had "exposed our whole flank and means of retreat." Although Leopold's decision was definitely not the cause of the German victory, it rendered the British military position untenable and led to the evacuation of the British Expeditionary Force at Dunkerque.
In the 18 days of fighting during the campaign, the Belgian army nonetheless fought bravely, with limited resources. Belgian casualties amounted to some 7,500 killed and 15,850 wounded. An additional 2,000 who had been taken as prisoners of war died in German captivity. Some Belgian soldiers and airmen managed to escape to Britain, where they formed the Independent Belgian Brigade and operated under the British for the remainder of the war.
Bitsch, Marie-Thérèse. Histoire de la Belgique. Paris: Hatier, 1992.; Bond, Brian. France and Belgium, 1939–1940. London: Davis-Poynter, 1975.; Mollo, Andrew, Malcolm McGregor, and Pierre Turner. The Armed Forces of World War II: Uniforms, Insignia, and Organization. New York: Crown Publishers, 1981.