Start of the tenth battle of the Isonzo

On 12 May 1917, as soon as day began to break, the Italian guns opened up along the whole front on the Isonzo, from Tolmin to the Adriatic. The fire soon grew to a strength this front had never yet known. General Luigi Cadorna was opening the Tenth Battle of the Isonzo, the first for half a year and the largest of all so far. This time he did not want merely to bite into the Karst plateau on the road to Trieste, as in the three autumn battles of 1916. He intended first to take the mountains north of Gorizia, and only then to deliver the decisive blow on the Karst.

Cadorna’s plan

After the ninth battle in November 1916, Cadorna spent the whole winter expanding the army. The oldest and youngest age groups were called up, and the factories worked flat out. According to the Austrian official history, in May 1917 the Italian army had 59 divisions, about 850 battalions and more than 5,000 guns. In April two groups of British heavy artillery, ten batteries, also arrived. This was only a small part of the help Prime Minister David Lloyd George had spoken of at the January conference in Rome, but the British had only about 150 such batteries in France, so it was no small gesture. The Allies, disappointed by the collapse of the Nivelle offensive, were pressing the Italians to attack at last and tie down the forces of Austria-Hungary.

Cadorna also considered a blow in the Tyrol, where since the spring of 1916 the Austrians had stood dangerously close to the Venetian plain, but the Isonzo took priority. The directives of 19 April divided the battle into three acts. First the artillery was to pound the whole front for several days, so that the defenders would not know where the main blow would fall and would not shift their reserves. Then General Luigi Capello’s new army, the “Gorizia Zone”, formed in March from part of the 2nd Army, was to advance. Its task was to take the chain of heights from Kuk and Vodice above Plava through Monte Santo and Monte San Gabriele to San Marco, which closed off the Gorizia basin to the north and east. Finally, the 3rd Army of the Duke of Aosta, Emanuele Filiberto, was to break through on the Karst and take the line from Mount Trstelj to the Hermada. During the battle the heavy batteries were to move from one army to the other. The battle was set for 7 May, but because of the rains it was postponed day after day.

Waiting on the other side

General Svetozar Boroević, commander of the Austro-Hungarian 5th Army, also known as the Isonzo Army, had never before had so strong a force. He expected the main blow on the Karst, however, and kept most of his reserves there. At the beginning of May the Italians carefully concealed their preparations, and the rain helped them. Then deserters began to come over, announcing an imminent offensive and saying that it would also include the mountains north of Gorizia. When the weather cleared, airmen spotted new camps behind the ridges of Korada and Kolovrat, and on 7 May many new batteries opened fire opposite XVII Corps, which was holding the heights above Plava and the Bainsizza plateau.

On 9 May Boroević asked the South-Western Front command in Maribor for permission to move one division to the Trnovo plateau, behind the threatened sector. Archduke Eugen, who had just been told by the high command that reinforcements were unlikely, refused. On 10 and 11 May the front suddenly fell quiet, and at the Isonzo Army headquarters in Postojna there was serious speculation as to whether the Italians, alone after the failures of the French and British and with Russia weakening, had given up the offensive.

12 May

The doubts were dispelled at dawn on 12 May. According to the Austrian official history, Capello’s army and the 3rd Army opened fire simultaneously, so that Boroević’s headquarters gained the impression that the battle had flared up along the whole front from Tolmin to the sea. According to some accounts, there was mist over Gorizia in the morning which hampered observation, and the 3rd Army opened full fire only at noon. The bombardment did not stop at night. The Italians then shelled roads, depots and the quarters of reserves. The Austrian artillery replied in order to pin down the Italian infantry gathering in the jumping-off trenches. Both sides also fired gas shells.

On the heights above Plava and at Gorizia the bombardment tore up the wire and buried the trenches, and in some sectors turned the positions into a field of craters. Command posts were shelled especially heavily. Already on the first day Boroević understood from the scale of the fire how wide the front of attack was to be: so many new batteries on the mountains opposite XVII Corps could not serve merely as a diversion. He again asked for the 106th Landsturm Infantry Division, and late in the evening, having received permission, sent it from the Vipava valley to the Trnovo plateau. At headquarters, however, it was still believed that the real blow would fall on the Karst, in the direction of Trieste.

Meanwhile the Italian command had troubles of its own. The commander of II Corps at Plava disagreed with Capello, who just before the battle had ordered him to limit the planned outflanking movement across the Isonzo to the north and to attack straight at the Kuk ridge. In the end he left his post, and on 13 May the corps was taken over by Capello’s chief of staff, General Pietro Badoglio. That same day Cadorna wrote to the minister of munitions that for the planned operations he needed at least 4–5 million medium and heavy calibre shells, but could count on only two and a half million.

The assault of 14 May

The bombardment lasted two and a half days, and on the morning of 14 May it rose to a hurricane of fire. At noon Capello’s infantry went in to attack. From Plava the Udine Brigade took Hill 383 at the first rush, and the Firenze Brigade reached the slopes of Kuk. In the evening a battalion of the Campobasso Brigade forced its way up a hidden path to the summit of Monte Santo, to the ruins of the monastery, but during the night Austrian reserves drove it out. At Gorizia all the attacks broke down in the barrage, and the 3rd Army’s subsidiary attack above the Vipava valley and on Fajti hrib also ended in failure. The following night Italian battalions crossed the Isonzo north of Plava, and Badoglio’s II Corps began to push up onto the Kuk ridge. The fighting for the mountains above Gorizia was to continue for more than a week, and on 23 May the weight of the battle shifted to the Karst.