The Wallonische-Infanterie Bataillon 373, commonly known as Légion Wallonie (earlier designations were Corps Franc Wallonie and Légion Belge Wallonie) was raised on 8 August 1941 from Belgian walloon volunteers with strong support from the Rexist movement under Leon Degrelle together with a few Russians, veterans from the White forces in the Russian Civil War.
Unlike some other volunteer formations, the volunteers kept their ranks from the Belgian Army when joining the Wehrmacht. Degrelle was refused the rank of Leutnant which he felt would suit his political status and served as Schütze but he would soon raise rapidly through the ranks.
In October the battalion was sent to the Eastern Front and on 2 November 1941 it disembarked at Dniepropetrovsk where it met up with the Italian units fighting in the east. It was attached to first 101. Leichte Infanterie-Division and later to 100. Leichte Infanterie-Division in January 1942, it was used behind the front until February 1942 when it was actions on the front against the Red Army.
In May it was briefly attached to the 68. Infanterie-Division and then to the 97. Leichte Infanterie-Division where it remained until November.
It was upgraded and transferred into the Waffen-SS in June 1943 as SS-Sturmbrigade Wallonien.

Commanders

Major Georges Jabobs (8 Aug 1941 - 30 Dec 1941)
Hauptmann Pierre Pauly (30 Dec 1941 - 1 Apr 1942)
Hauptmann Georges Tchekhoff (1 Apr 1942 - 1 June 1943)

Manpower strength

Order of battle

Stab
1. Kompanie
2. Kompanie
3. Kompanie
4. schw. Kompanie

Notable members

Curt Sjögren (Swedish volunteer in the Belgian manned unit, KIA 22 April 1942 at Zaporozje)

Illustrations of the original unit standard and the standard of the third company
 
(Courtesy of Wikimedia)

Léon Degrelle (center) and Jules Mathieu (left) just before the departure from Belgium

(Courtesy of Die Deutsche Wochenschau/Ivan)

The volunteers marching towards the train station on 8 August 1941 behind the colors with the Burgundy Cross

(Courtesy of Die Deutsche Wochenschau/Ivan)

The volunteers marching towards the train station on 8 August 1941

(Courtesy of Die Deutsche Wochenschau/Ivan)

Recruitment propaganda

(Courtesy of Military Postcards)

Sources used

Christopher Ailsby - Hitler's Renegades: Foreign nationals in the service of the Third Reich
Eddy De Bruyne & Marc Rikmenspoel - For Rex and for Belgium: Leon Degrelle and Walloon Political & Military Collaboration 1940-45
Lars Gyllenhaal & Lennart Westberg - Svenskar i krig 1914-1945
Georg Tessin - Verbände und Truppen der deutschen Wehrmacht 1933-1945

Reference material on this unit

Eddy De Bruyne & Marc Rikmenspoel - For Rex and for Belgium: Leon Degrelle and Walloon Political & Military Collaboration 1940-45
R. V. Zavadsky - Svoya chuzhaya voyna. Dnevnik russkogo ofitsera vermakhta 1941–1942