Battles of the Isonzo

The Battles of the Isonzo were twelve battles fought in 1915–1917 on the Isonzo, in Slovene the Soča, a river which then flowed through Austrian territory along the border with Italy. For two years and three months the Chief of Staff of the Italian army, General Luigi Cadorna, threw his armies again and again against the Austro-Hungarian positions on the hills above the river and on the rocky Karst plateau. He wanted to take Gorizia and Trieste and then open a way into the heart of the monarchy. The defence was directed by General Svetozar Boroević, who almost always had fewer men and guns than his opponent, but defended favourable ground and quickly patched every breach. In eleven offensives the Italians took Gorizia, Monte San Michele, Monte Santo and most of the Bainsizza plateau, but did not break the front and did not reach Trieste. In that time the two sides lost more than a million killed, wounded and missing. In autumn 1917 the exhausted Austrians asked the Germans for help, and in the twelfth battle, at Caporetto, together they drove the Italian army from the Isonzo all the way back to the Piave.

Name and dates

The Italians speak of the battles of the Isonzo (battaglie dell’Isonzo), the Germans and Austrians of the Isonzoschlachten, and the Slovenes, on whose land most of the fighting took place, of the Soča front (soška fronta) and the Soča battles (soške bitke). The numbering was given to the battles by the Italian Supreme Command and was also adopted by the Austrians, although it was rather arbitrary. Both sides saw the Third and Fourth Battles in autumn 1915 as a single two-month offensive. The British official history regards the Seventh, Eighth and Ninth Battles in autumn 1916 as three stages of one battle, separated by pauses for regrouping. The Austrians, for their part, considered that the scattered attacks of March 1916 did not deserve the name of a Fifth Battle at all. The first eleven battles were Italian offensives, and the twelfth, known as the Battle of Caporetto, an Austro-German one.

The dates of the individual battles differ in the sources by a day or several days, and the end of the twelfth by as much as two weeks. We adopt the dates 23 June 1915 – 9 November 1917: from the first day of the first battle to the day on which the last Italian rearguards crossed to the western bank of the Piave and Cadorna handed over command to his successor. The fighting on the Isonzo began earlier, however, as soon as the Italians crossed the border on 24 May 1915. Slovene works count the Soča front from that day to 28 October 1917, when the last Italian units left the river.

Background

Italy entered the war on the side of the Entente under the Pact of London, which promised it, among other things, Trentino, South Tyrol, Trieste, Istria and part of Dalmatia. On 23 May 1915 it declared war on Austria-Hungary, and the following night its troops crossed the border. The border ran unfavourably for the Italians. In the north, in Trentino, Austrian mountains cut deep into their territory, and in Carnia and the Dolomites it ran through the high Alps. The only sector where a large army could attack was the Isonzo valley in the east, and beyond it the Karst, through which ran the road to Trieste and Ljubljana. There Cadorna sent his main forces, intending to stand on the defensive on the other sectors.

The Isonzo front was about 90 kilometres long. It began in the Julian Alps, on the peaks of Rombon above Bovec and the Krn massif above Kobarid, descended the river valley to Tolmin, where the Austrians held a bridgehead on the western bank, and continued along the river to Plava. On the eastern bank here rose the Bainsizza plateau (Slovene Banjšice) and the heights of Monte Santo and Monte San Gabriele, which dominated Gorizia. The town itself was protected by a bridgehead on the right bank, with Mount Sabotino and the hills of Oslavia and Podgora. South of Gorizia began the Karst, a bare limestone plateau with Monte San Michele on its western edge and the Hermada above the sea. The British official history writes that the Italians, attacking anywhere except the narrow coastal strip, had to attack uphill against a natural fortress, and that their real enemy was the ground rather than the Austrians.

At the start of the war the Italians had a great numerical superiority. Cadorna had 35 divisions, while according to the British official history Boroević, whose new Fifth Army was still assembling, had seven divisions on the Isonzo on 23 May. Austria-Hungary was taken up with the offensive in Galicia, which had begun on 2 May at Gorlice, and with the war against Serbia. Conrad preferred to stay on the defensive on the Italian front, and sent divisions there gradually from the Balkans and Galicia. The defenders had time, however, because for several weeks the Italians advanced very cautiously and reached the river only in June. The Austrians withdrew behind the Isonzo, onto the hills of the Gorizia bridgehead and the edge of the Karst, and dug in there, cutting shelters and machine-gun posts into the rock. The supreme commander of the troops facing Italy was Archduke Eugen.

1915: four battles for Gorizia and the Karst

The First Battle of the Isonzo lasted from 23 June to 7 July 1915. The Second Army of General Pietro Frugoni and the Third Army of the Duke of Aosta, Emanuele Filiberto, had more than a twofold numerical superiority, but too few heavy guns, too little ammunition and too few wire-cutters. The attacks on Monte San Michele, the Sei Busi hill, the Gorizia bridgehead and the Tolmin bridgehead broke down on the barbed wire and in machine-gun fire. The Italians crossed the Isonzo at Sagrado and took scraps of ground at the foot of the Karst. As early as 18 July the second battle began, in which the Third Army, with twice as many guns as the defenders, stormed above all Monte San Michele. Twice it took the summit and twice it was thrown off it. The only clear success was the capture by Alpini of the Batognica summit in the Krn massif. When Cadorna broke off the offensive on 3 August, both sides had lost more than 40,000 men each, and the front had moved at most a few hundred metres.

On the Karst the fighting was particularly cruel. Trenches could not be dug in the bare rock, so the defenders sheltered behind low walls of stones, and shells smashed them into sharp splinters which increased the losses on both sides. In summer there was no water, in winter the soldiers froze in the rain and snow on the exposed plateau. The British official history notes that in the Isonzo battles there were exceptionally many wounded for each man killed, probably because of rock splinters.

In autumn Cadorna gathered heavy guns from the fortresses and the navy and on 18 October began the third battle, this time along the whole front. According to the Italian official history 338 battalions with more than 1,300 guns attacked a Fifth Army less than half as strong. The offensive was also meant to relieve Serbia, which Austria-Hungary and Germany had attacked on 6 October, followed soon afterwards by Bulgaria. By 4 November the Italians had lost about 67,000 men and taken only isolated stretches of trench. As early as 10 November the fourth battle began, which the Austrians called the “parliamentary” battle, because in their view Cadorna wanted to show a success before the opening of the Italian parliament on 1 December. The Italians took the ridge below the church at Oslavia and several stretches of trench, and from 18 November their artillery began systematically to destroy Gorizia. By the beginning of December they had lost almost 49,000 more men. According to the British official history, in the seven months of 1915 Italy lost about 250,000 men on all fronts and gained no tactical or strategic advantage. Gorizia, Monte San Michele and Sabotino remained in Austrian hands.

1916: Gorizia and the autumn “shoulder blows”

Cadorna began the fifth battle, in March 1916, at the call of the French fighting at Verdun. The scattered attacks from 11 to 16 March cost each side about 2,000 men and brought no gains. Nor did they prevent the Austrians from moving several divisions from the Isonzo to Tyrol, from where on 15 May Conrad struck in the Trentino offensive. The Italians then had to send a large part of their troops into the mountains, and for several months there was relative calm on the Isonzo.

When the Trentino offensive had been halted and Austria-Hungary had to send many divisions east against Brusilov, Cadorna secretly moved more than a dozen divisions and hundreds of heavy guns from the mountains to the lower Isonzo. On 6 August the sixth battle began, the Italian army’s first great victory. That same day the Italians took Mount Sabotino, which the Austrians had held since the beginning of the war, and the summit of Monte San Michele. On 8 August the defenders gave up the Gorizia bridgehead, on 9 August the first Italian units entered the town, and the Austrians abandoned the Doberdò plateau, the northern part of the Karst. On the new line, on the hills east of Gorizia, the Italians got stuck, however, just as before, and on 17 August Cadorna halted the attack. The front had moved forward 4–6 kilometres on a sector of about 24 kilometres, and the two sides together had lost more than 90,000 men. The victory aroused enormous enthusiasm in Italy, and soon afterwards Italy declared war on Germany as well.

In the autumn Cadorna tried to wrest the rest of the Karst from the Austrians step by step. In the Seventh (14–18 September), Eighth (9–12 October) and Ninth Battles (31 October – 4 November) his Third Army, supported by the Second Army at Gorizia, struck briefly, for three or four days, and broke off the attack as soon as the losses ceased to match the gains. Italian historians call these attacks “shoulder blows” (spallate). The Italians took San Grado di Merna above the Vipava, the ruins of the village of Nova Vas and, in November, the hills of Veliki Hribach, Pečinka and the lower summit of Fajti hrib. For two days in November Boroević had not a single battalion left in reserve, but the Austrians occupied a new line before Kostanjevica and again stopped the attack. Each of these battles cost the two sides between ten thousand and several tens of thousands of men. On 16 October Boroević wrote to the Supreme Command that since mid-August his army had lost about 100,000 men in battle. For the winter both sides stayed in their positions, and in the mountains above the upper Isonzo they fought frost and snow. The Austrians built more than 240 kilometres of cableways on this front, and the road over the Vršič pass was built by Russian prisoners of war, several dozen of whom were killed by an avalanche in March 1916.

1917: Kuk, Vodice and the Bainsizza

The tenth battle, from 12 May to 5 June 1917, was the largest yet. Cadorna threw about half his army into it with stronger artillery than ever before, and this time the attack also took in the mountains north of Gorizia. The newly formed army of General Luigi Capello took the ridge of Kuk and Vodice above Plava, but did not take Monte Santo. On the Karst the Third Army broke through the front at Jamiano on 23 May and came up to the Hermada, the last great obstacle before Trieste, but on 4 June a counter-attack by Boroević took most of its gains back. The Italians lost about 160,000 men, and according to Capello and Cadorna the first signs of slackening discipline appeared in some units.

The eleventh battle, from 17 August to 12 September 1917, was the largest offensive of the Italian army in the whole war. Cadorna concentrated 51 divisions on the Isonzo, three quarters of his infantry, and according to the Austrian official history about 5,200 guns and trench mortars. On the night of 18–19 August Capello’s Second Army crossed the Isonzo above Plava and within a few days took most of the Bainsizza plateau, advancing about 10 kilometres, and on 24 August it climbed Monte Santo. Boroević withdrew his troops to a new line and held Monte San Gabriele, which was fought over until the middle of September. On the Karst the Third Army stopped again before the Hermada. It was the greatest territorial success of the Italians on the Isonzo, but not a breakthrough. The troops on the plateau, without roads or water and with their artillery far behind, could go no further, and Cadorna, who had lost about 300,000 men in the two battles of 1917, informed the Allies on 21 September that he was going over to the defensive.

The Austrians held, but their official history called the victory a Pyrrhic one. The command feared that the Isonzo front would not survive a twelfth such battle. The Chief of Staff, General Arthur Arz von Straußenburg, decided to go over to a counter-offensive before the winter, and on 26 August Emperor Charles I turned to Emperor Wilhelm II for help. The Germans sent to the Isonzo a specialist in mountain warfare, General Konrad Krafft von Dellmensingen, and after his reconnaissance agreed to a joint attack from Tolmin.

Caporetto

On 24 October 1917 the new German Fourteenth Army of General Otto von Below, made up of German and Austro-Hungarian divisions, struck on the upper Isonzo between Bovec and Tolmin, at the weakest point of the Italian Second Army. After a night gas bombardment and a short artillery barrage the infantry advanced in rain and fog along the valley floor, and by the afternoon of the first day it was in Kobarid, in Italian Caporetto. Within three days the whole Italian front from the Carnic Alps to the sea collapsed. Cadorna ordered a retreat first behind the Tagliamento and then behind the Piave, more than a hundred kilometres from the starting line. Behind the army fled hundreds of thousands of civilians from Friuli and Venetia. The Duke of Aosta’s Third Army, which had bled for two years on the Karst, withdrew in good order, but the Second Army ceased to exist as a fighting force. On 9 November the last Italian rearguards crossed the Piave, and Cadorna handed over command to General Armando Diaz. The twelfth battle ended the fighting on the Isonzo. The front came to a halt on the Piave and in the Monte Grappa massif.

Casualties

The casualty figures are incomplete and often cover different periods, so all totals are approximate. According to tables based on the data of both sides, the Italians lost about 645,000 killed, wounded and missing in the first eleven battles, and Austria-Hungary between about 450,000 and 500,000, about 1.1 million men in all. The bloodiest were the two battles of 1917, in each of which the Italians lost about 160,000 men and Austria-Hungary between about 75,000 and more than 100,000. To this must be added tens of thousands of sick, because dysentery, typhus and frostbite spread in the rocky trenches of the Karst and in the mountains. Slovene works estimate that more than 300,000 soldiers of both sides were killed on the Isonzo.

In the twelfth battle the Italians lost, according to various works, between 10,000 and 13,000 killed, about 30,000 wounded and between 265,000 and nearly 300,000 prisoners, as well as more than 3,000 guns, almost half their artillery. The losses of the Central Powers are estimated at about 70,000 men. Together with Caporetto, all the Battles of the Isonzo cost the two sides about one and a half million men.

Civilians also suffered heavily. Gorizia, in which, according to the Austrians, about 2,500 of its 30,000 pre-war inhabitants remained in autumn 1915, was largely destroyed. According to Slovene works the Austrian authorities removed about 80,000 Slovenes from the Gorizia area and the Soča valley, and the Italians between 10,000 and 12,000 from the areas they occupied. Many refugees died in camps and of disease.

Significance

The Battles of the Isonzo were for Italy what the fighting on the Western Front was for France and Britain: positional warfare, in which great offensives brought gains measured in hundreds of metres, and most of them cost tens of thousands of soldiers. In two years the front moved forward at most some fifteen kilometres. Cadorna believed that the war would end in the exhaustion of men and means and that Austria was closer to it than Italy, and indeed in 1917 Boroević’s army was close to the end of its strength. The endurance of the defenders, among whom fought soldiers of almost all the nations of the monarchy, from Hungarians and Dalmatians to Bosnians, Romanians and Tyroleans, earned Boroević a reputation as a master of defence.

The exhaustion of Austria-Hungary, however, brought the Germans into the last battle, and their participation turned two years of struggle into an Italian defeat. Caporetto almost knocked Italy out of the war and became a national trauma, but the Italian army did not fall apart. A year later, in October 1918, it set out from the Piave on its last, victorious offensive, and Trieste, to which the Italians had failed to break through on the Isonzo for two years, they entered only in the last days of the war. The memory of the Battles of the Isonzo is kept by great cemeteries and ossuaries, above all the Italian shrine at Redipuglia at the foot of the Karst, where about 100,000 soldiers lie, and by the museum of the First World War in Kobarid, opened in 1990.