The Union Nationale des Combattants (UNC) started as an association of French veterans from the First World War[1]. It was founded on 11 November 1918 (Armistice Day) and located at Rue Lafayette 13 in Paris[2]. They operated the seller service Service des Ventes de l’U.N.C (SDV) that offered glass stereoviews with images from the war. The slides were manufactured by La Stéréoscopie Universelle (LSU).
A catalog[2] shows that the slides were sold in series of 10. Some series were available in both 45x107mm and 6x13cm formats, others only in the 45x107mm format. The slides were numbered using a unique numbering scheme. Some of the slides are re-used LSU views with just a new number added.

References
- Union Nationale des Combattants – via fr.wikipedia.org
- Vues Stéréoscopiques de guerre, Service des Ventes de l’U.N.C – via greatwarin3d.org