The 2nd Battalion deployed to France on 2 October 1939 and was transferred to the 145th Brigade in the 48th Division in March 1940. This brought it alongside the 5th Battalion in the division's 144th Brigade, which had arrived in France on 15 January 1940. In May 1940, during the Battle of France, the German breakthrough at Sedan precipitated a retreat to Dunkirk. The 5th Battalion marched in 83 hours with little food or sleep before eventually picking up transport at Tournai where, on 19 May, the 2nd Battalion lost 194 men killed or missing in a matter of minutes to an airstrike. The regiment gained some respite on 20 May, when the two battalions held positions along the River Escaut (Scheldt) for two days before the British Expeditionary Force resumed its retreat. On 25 May, the 2nd Battalion, having by now suffered 219 casualties, became part of Somer Force. This mixed group of units under the command of Brigadier Nigel Somerset, until recently the 2nd Battalion commanding officer, fortified Cassel on the outer perimeter around Dunkirk. The Germans probed the town the next day and began assaulting it on 27 May. Somer Force held out for two days, eventually attempting to withdraw under orders on the evening of 29 May, but few made it to Dunkirk. The 2nd Battalion suffered 678 casualties at Cassel, 484 of them POWs. Meanwhile, the 5th Battalion was given a similar task at the villages of Arneke and Ledringhem, some north-west of Cassel. The battalion took up positions on 26 May, and the first attacks came the next day. By 28 May, the battalion had concentrated at Ledringhem, where it was surrounded, and it withdrew under orders in the early hours of 29 May. The survivors reached Bray Dunes before dawn the next day and were subsequently taken off the beach by little ships. The stand at Ledringham had cost the battalion 87 killed, and when it reassembled in the UK it was 400 strong.