From 1917: War, Peace, and Revolution, by David Stevenson (OUP Oxford, 2017), Kindle pp. 205-207:
On Wednesday 24 October 1917 German and Austrian forces launched one of the most daring attacks of the war. Breaking through Italian positions in the upper Isonzo river valley, within two weeks they had advanced over 100 miles. Almost half the Italian army were killed, wounded, or captured, or discarded their weapons and streamed to the rear. Territory that had taken more than two years and 900,000 casualties to capture was abandoned within hours. Amid the dreary litany of failed offensives and attrition battles, the name of Caporetto stands out, and in Italy has remained a shorthand for rout and fiasco. Even so, for most of the war it had been the Italians, not the Central Powers, who had been on the attack, in conditions often even worse than on the Western Front. In part, the collapse grew out of overstretch. To understand how the Italian army became so exposed, we must consider not only the Twelfth Battle of the Isonzo (as the Italians officially entitled Caporetto), but also the Tenth and Eleventh. It is further necessary to survey the operations themselves, from Austro-German breakthrough to Italian recovery. Devastating though Caporetto was, in many ways it strengthened Italy’s war effort.
Between 1882 and 1914 Italy had regularly renewed its Triple Alliance with Germany and Austria-Hungary. In 1914 it stayed neutral, and in May 1915 it joined the Allies, following the secret Treaty of London concluded with Britain, France, and Russia in April. Italy’s nineteenth-century national unification had left some 800,000 Italian-speakers under Austrian rule. But the Allies promised Italy not only the ethnically Italian areas in the Trentino and the environs of Trieste, but also the German-speaking South Tyrol and the Slovenian and Croatian territories of Istria and Dalmatia. And to incorporate any of these areas the Italians would have to conquer them. As France and Britain would enter any peace negotiations handicapped unless they dislodged the German army from France and Belgium, so too would Italy unless it dislodged the Austro-Hungarian army from the areas promised. In both theatres, if the Central Powers defended successfully they would win.
In both, however, they defended with one hand tied behind their backs. The Germans kept on average a third of their field army on the Eastern Front. The Austrian army was smaller, and because of its commitments in the Eastern and Balkan theatres, in 1917 only one-fifth of it faced Italy. Even so, this fifth included some of its best units, and the Italian war, imposed by an aggressor, was less unpopular than were other fronts. The Austrians also benefited from geography. The Front ran for 375 miles from the Swiss border to the Adriatic Sea, but much was so mountainous as to be completely unsuitable for operations (though fighting none the less occurred—trenches being dug in ice fields and thousands perishing in avalanches or freezing to death). The exceptions were the Trentino and the lower stretches of the Isonzo. The Trentino was one of the Italians’ target areas, but it was remote from the Austro-Hungarians’ urban and industrial centres, and easily defended. Projecting southwards, it formed an obvious jumping-off point for driving into the Po valley and cutting off the main Italian forces. For these reasons the Austrians had attacked there in May 1916, and although the Italians had rallied with assistance from Russia’s Brusilov offensive, the Austrians had pushed them closer to the plateau edge. They would be still more vulnerable if Austria-Hungary attacked again. None the less, the fighting concentrated on the Isonzo. Between May 1915 and September 1917 no fewer than eleven battles were fought there. In rocky terrain, bitterly cold in winter, it was hard to excavate dugouts and trenches, and stone splinters magnified the impact of bombardment, both sides sheltering in cliff-side caves. The quantities of heavy artillery, gas, and aircraft were smaller than in France, and to begin with the Italians were poorly equipped. Only in August 1916 did they achieve their first big success by switching reinforcements rapidly from the Trentino battle, gaining surprise, and taking Gorizia. Three more Isonzo battles that autumn, however, led to no further progress, and left the army exhausted before a prolonged winter pause. By this stage the Italians held most of the Isonzo except for an Austrian bridgehead round Tolmino. But east of Gorizia a natural ‘amphitheatre’ of encircling peaks overlooked their positions, and to the north and south lay the limestone plateaux of the Bainsizza, the Ternova, and the Carso. Rising to over 2,000 feet, the plateaux were waterless, treeless, and largely devoid of roads and settlement. But beyond them lay no comparably short and defensible line between the Italians and the goals set by their commander, General Luigi Cadorna, of Trieste (Austria-Hungary’s one significant port) and Ljubljana, whence a further advance might threaten Vienna.
At first the Italians fought against Austria-Hungary alone, declaring war on Germany only in August 1916. They sent contingents to the Balkans but not the Western Front, and the Germans stayed out of the Italian theatre. The other allies resented the high price paid for Italian intervention, and the lack of Italian progress.