World War II had a massive impact on the Métro. Services were limited and many stations closed. The risk of bombing meant the service between Place d'Italie and Étoile was transferred from Line 5 to Line 6, so that most of the elevated portions of the Métro would be on Line 6. As a result, Lines 2 and 6 now form a circle. Most stations were too shallow to be used as bomb shelters. The French Resistance used the tunnels to conduct swift assaults throughout Paris.