In 1936 Somua produced a railcar for PLM, the XS 1 to 11.
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Named the JL 12 and equipped with a flex-fuel four cylinder engine, the vehicle did not impress the "Commission des plans de modernisation de l’automobile" which decided in 1946 to merge Somua with Willème and Panhard to form a new company, the Générale française de l'automobile (GFA).
On 17 May the Army had already contacted a subsidiary of Schneider et Cie — the Société d'Outillage Mécanique et d'Usinage d'Artillerie (or SOMUA) based at Saint-Ouen — to build a prototype.