in september 1939, world war ii broke out and the stations of "croix-rouge" and "cluny-la sorbonne", considered too close to other stations, were closed. after these closures, the line encompassed 20 stations all together. on 3 june 1940, the bombing of citroën factories damaged the tunnel of line 10 between "chardon-lagache" and "mirabeau". as a result, service was restricted to the section of "gare d'austerlitz-beaugrenelle", which became "charles-michels". three days later, a ferry on its own tracks was put into service running between "beaugrenelle" and "porte d'auteuil". normal service was reestablished on 8 june.