Soon after being ousted, Mussolini was rescued by a German commando in Operation Eiche ("Oak"). The Germans brought Mussolini to northern Italy where he set up a Fascist puppet state, the Italian Social Republic. Meanwhile, the Allies advanced in southern Italy. In September 1943, Naples rose against the occupying German forces. The Allies organized some royalist Italian troops into the Italian Co-Belligerent Army, while troops loyal to Mussolini continued to fight alongside Nazi Germany in the "Esercito Nazionale Repubblicano", the National Republican Army. In addition, a large Italian resistance movement started a long guerrilla war against the German and Fascist forces. As consequence, the country descended into civil war, with the Italian Co-belligerent Army and the resistance movement, supported by the Allies, contended the Social Republic's forces and its German allies.