In World War I, joint German-Austrian victory over the Italian Army Oct 1917 at Caporetto, a village on the river Isonzo in northwest Slovenia. The German commander, General Karl von Bülow, broke through Italian lines on the Isonzo and forced an Italian retreat to fall back onto the Piave line.
At the end of Sept 1917 the Italian offensive against the Austrians in the Isonzo area ended, but in the summer the German Staff had planned an offensive in the area and during Oct the Austrians were joined by substantial German reinforcements. The Italians were expecting an attack from the north but a massive German force was assembled in great secrecy at the southern end of the Italian front and on 24 Oct, after a heavy artillery bombardment, von Bülow broke through the Italian lines west of the Isonzo and headed for Caporetto. Heavy fighting continued throughout the following day, with delays in sending reserves weakening Italian resistance. As the Germans penetrated deeper, so the flanks of the remaining Italian line were threatened and had to fall back. By 26 Oct Caporetto had fallen and masses of Italian troops were in headlong retreat. Eventually General Luigi Cadorna authorized a full retreat, which continued some 95 km/60 mi to the line of the river Piave before the Italian defense could be stabilize
d.
The sudden collapse of the Italians took von Bülow by surprise and he was unable to bring up reserves or take advantage of the situation. As it was, the Austro-German forces merely moved slowly forward in the wake of the Italians, taking Gorizia, Cividale, and Udine as they did so. Von Bülow's forces crossed the river Tagliamento, the advanced Italian line, 3 Nov 1917 and broke through Italian outposts but their advance was halted by the Piave line.