The Union Nationale des Combattants (UNC) started as an association of French veterans from the First World War. It was founded on November 11, 1918 (Armistice Day) and located at 13, Rue LaFayette in Paris. They operated the seller service Service des Ventes de l’U.N.C. that offered glass stereoviews with images from the war. The slides were manufactured by La Stéréoscopie Universelle (LSU).
A catalog [1] shows that the slides were sold in series of 10. Some series were available in both 45x107mm and 6x13cm formats, others only in 45x107mm format. They were numbered using a unique numbering scheme. Some of the slides are re-used LSU views with just a new number added.

References
- The Great War in 3D, Catalog of SDV