Despite having been part of the pre-war Triple Alliance with Austro-Hungary and Germany, in 1914 Italy had remained neutral. Over the next few months both sides attempted to convince the Italians to join them. The British and French had a big advantage in this effort – the Italians had claims on two parts of the Austro-Hungarian Empire. At the end of the Italian Wars of Independence two major Italian speaking areas had remained within the Empire – the Trentino, north of Lake Garda, and the Littoral, the lower Isonzo valley and the area around Trieste. The Allies were able to promise that Italy would receive these areas at the end of the war; and so on 23 May 1915 Italy declared war on the Allied side.
The Italians had one major problem in 1915. Their 400 mile long border with the Austro-Hungarian Empire ran through the Alps. In some places the mountains were so rugged that no offensive could even be contemplated. The only real gap in the mountains led along the Adriatic coast to Trieste, but that was a dead end, surround by more mountains. If the Italians were to launch an effective assault on the Austrians, then it would either have to be on the Trentino, or towards the Isonzo valley.
The Italian commander in chief, General Luigi Cardorna, chose to attack on the Isonzo. A breakthrough on the Trentino would merely eliminate an Austrian salient, whereas a breakthrough on the Isonzo might lead to an advance into the heart of the Empire, and even threaten Vienna. The only problem with this grand plan was that the mountainous terrain on the Isonzo front would turn out to be ideally suited for a defensive battle.
While not the highest of mountains, the rocky slopes and ridges of the southern Julian Alps and the Carso Plateau meant that some of the fighting took place at over 2000 feet. However, the role the mountains played in the Austrian defences should not be overplayed. The town of Gorizia, on the Isonzo river, was only captured during the sixth battle of the Isonzo, yet it lies on the western flank of the mountains. The Italian advance during eleven battles on the Isonzo never penetrated to the higher mountains to the east.
Cardorna began the war with his “First Offensive Leap” of 23-27 May 1915. On the Isonzo front the Italians advanced to the river in some places, and reached close to it in others, but Gorizia remained out of reach. A second attack in early June failed to make any progress, and so Cardorna prepared for his first major attack.
Two Italians armies were involved in the fighting on the Isonzo Front. To the north was the Second Army under General Frugoni, while to the south was the Third Army, under the Duke of Aosta. By the end of the first battle these two armies contained 18 divisions, supported by 700 guns, although only 200 of these seem to have been the heavy guns needed to break the Austrian wire.
They faced the Austrian Fifth Army, under General Boroevic. At the end of the battle he commanded eight divisions, and was always outnumbered by at least two to one. In May 1915 the Austrians were still fighting a three front war, against Russia, Serbia and Italy, and troops were in short supply. Luckily for Boroevic and his men the Austrians had prepared well for an attack along the Isonzo, dynamiting shelters into the rocks and extending the local cave system to create a maze of fortifications in the hills and mountains along the Isonzo.
The first battle of the Isonzo began with a week long artillery bombardment, starting on 23 June. While the bombardment was still going on, they launched a series of unsuccessful probing attacks at Podgora, Oslavice and Peuma, each of which failed, as did an attack on Sabotino made on 29-30 June.
The main infantry attack was made on 30 June, on a 21 mile front. Little progress was made, although a small foothold was made on the eastern bank of the Isonzo.
On 2 July two Italian divisions launched an attack towards the Carso Plateau, on the southern part of the line. This was then followed by a more general assault, from Podgora to the Doberdo Plateau. Despite a six-to-one numerical superiority on parts of the line, the Italians only advanced one mile, while at the same time they were expelled from the crucial hills overlooking Gorizia, making future attacks on the town much more difficult.
The first battle of the Isonzo cost the Italians 14,947 casualties, including 1,500 men taken prisoner. The Austrians lost 9,948 men, a higher proportion of their army on the Isonzo, but not enough to win the Italians a breakthrough. The search for that breakthrough would result in ten more Italian attacks on the Isonzo, none of which would achieve the decisive breakthrough.