The Western Switzerland Railways (Chemins de fer de la Suisse Occidentale, shortened to Suisse-Occidentale; SO or S-O), were initially a joint operation of three Swiss railway companies, but these companies merged on 1 January 1872. The company was called the Western Switzerland–Simplon Railways (Chemins de fer de la Suisse Occidentale et du Simplon, shortened to Suisse-Occidentale–Simplon; SOS or SO-S) from 28 June 1881. The SOS merged with the Bernese Jura Railways (Chemins de fer du Jura bernois; JBL) to form the Jura–Simplon Railways (Compagnie des Chemins de Fer Jura–Simplon; JS) on 1 January 1890.