Continuing ambitions and intrigue on the part of Léon Degrelle brought the 373rd Walloon Battalion from the German Army into the Waffen-SS in May, 1943. With additional recruits and depot replacements, the SS formed them into the 5th SS "Wallonien" Volunteer Assault Brigade, consisting initially of one battalion of infantry with additional companies of anti-tank, assault gun, antiaircraft, and engineer troops. After training at Wildflecken, the brigade was sent in November, 1943, to the SS "Wiking" Division as a reinforcement. Caught in an encirclement of most of the German XXXXII corps at the end of January, the brigade participated in the breakout with heavy losses but emerged intact. While reforming that summer, a battalion battle group fought near Lake Pskov in August as a reinforcement to beleaguered German forces.
Degrelle and the SS leadership now exploited the Belgian collaborationist refugee flood to expand the brigade to divisional size. The 28th SS "Wallonien" Volunteer Mechanized Infantry Division was formed on 18 September 1944 from the 1800-man assault brigade and these new recruits. It consisted of the 69th and 70th Mechanized Infantry Regiments, and artillery regiment and battalions of reconnaissance, antitank, assault gun, engineer and signal troops, but less than half of these were filled out by the war's end. In the final months of the war, only a regimental-sized battle group became ready and it fought with the III Germanic Corps in West Prussia in March and April, carrying out its last operations alongside the Flemish volunteers in the Stettin region. The survivors moved west and surrendered to British forces near Schwerin, joining the bulk of the "division," which had not left its training camps.