to organise the Dunkirk evacuation and build a defensive line. While more than 330,000 Allied troops were rescued, the British and French sustained heavy casualties and were forced to abandon nearly all their equipment; around 16,000 French and 1,000 British soldiers died during the evacuation. The British Expeditionary Force alone lost some 68,000 soldiers during the French campaign. Prelude On 10 May 1940, Winston Churchill became Prime Minister of the United Kingdom. By 26 May, the BEF and the French 1st Army were bottled up in a corridor to the sea, about deep and wide. Most of the British forces were still around Lille, over from Dunkirk, with the French farther south. Two massive German armies flanked them. General Fedor von Bock's Army Group B was to the east, and General Gerd von Rundstedt's Army Group A to the west. Both officers were later promoted to field marshal. Halt order On 24 May, Hitler visited General von Rundstedt's headquarters at Charleville. The terrain around Dunkirk was thought unsuitable for armour. Von Rundstedt advised him the infantry should attack the British forces at Arras, where the British had proved capable of significant action, while Kleist's armour held the line west and south of Dunkirk to pounce on the Allied forces retreating before Army Group B. Hitler, who was familiar with Flanders' marshes from the First World War, agreed. This order allowed the Germans to consolidate their gains and prepare for a southward advance against the remaining French forces. Luftwaffe commander Hermann Göring asked for the chance to destroy the forces in Dunkirk. The Allied forces' destruction was thus initially assigned to the air force while the German infantry organised in Army Group B. Von Rundstedt later called this "one of the great turning points of the war." The true reason for the decision to halt the German armour on 24 May is still debated. One theory is that Von Rundstedt and Hitler agreed to conserve the armour for Fall Rot ("Case Red"), an operation to the south. It is possible that the Luftwaffe's closer ties than the army's to the Nazi Party contributed to Hitler's approval of Göring's request. Another theory—which few historians have given credence—is that Hitler was still trying to establish diplomatic peace with Britain before Operation Barbarossa (the invasion of the Soviet Union). Although von Rundstedt after the war stated his suspicions that Hitler wanted "to help the