With the other "La Galissonnière"-class cruisers, "Jean de Vienne" was at Algiers at the time of the Armistice, in late June 1940. On 3 July, at Mers-el-Kébir, Admiral Sommerville, commander of Force H, had to deliver an ultimatum to the French admiral commanding the French battleship squadron, either to join the British or to be attacked. As negotiations dragged on, the French Admiralty signaled in a radio message in clear, that the Algiers cruisers had been ordered to join the battleship squadron off Mers-el-Kébir. The British Admiralty warned Admiral Somerville and hurried him to put an end to the negotiations with the French admiral and to open fire. So the six cruisers, too far to intervene, made for Toulon instead, where they arrived the day after. "Jean de Vienne" remained there, out of action until she joined the French High Seas Force in March 1941. In January 1942, "Jean de Vienne" was sent to rescue the liner "Lamoriciere", whose sinking in a winter tempest, off the Balearic Islands, caused more than 300 deaths.