At the time of the outbreak of World War II in September 1939, only two of the ships had been commissioned, with the third being brought into service three months after the war started. Their only significant pre-war task was undertaken by "Beograd" in May 1939, and involved the transportation of a large portion of Yugoslavia's gold reserve to the United Kingdom for safekeeping. On 24 January 1940, "Ljubljana" ran into a reef off the Yugoslav port of Šibenik. The hull side was breached and despite efforts to get the ship into the port, it sank close to shore, and some of the crew swam to safety. One crew member died, and the captain was arrested pending an investigation.