When the German invasion of Belgium began on 10 May 1940, the division was alerted for movement into Belgium under the Dyle Plan. Assigned to the 4th Army Corps of the 1st Army, the "15e DIM" recalled the 27th Infantry Regiment, which was at Sissonne on maneuvers. The 134th Infantry Regiment was sent ahead to Saint-Quentin, while the "4e GRDI" was detached to the corps headquarters as part of "Groupement Arlabosse", led by its commander. On the next day the division moved by road from Chauny to Gembloux through Tergnier, Saint-Quentin, Le Cateau, Binche, La Louvière, Gosselies, and Tongrinne, setting up its headquarters at Tongrinne. The 4th and 134th Infantry Regiments began moving into positions on 12 May, with a battalion from each regiment occupying the sector of the 1st Moroccan Division, which had not yet arrived, from Ernage to the northern part of Gembloux. "Groupement Arlabosse" was briefly transferred back to the division that day but again detached to the 1st Moroccan Division at noon.