Battles of the Isonzo

The Battles of the Isonzo (known as the Isonzo Front by historians, Slovene: soška fronta) were a series of 12 battles between the Austro-Hungarian and Italian armies in World War I mostly on the territory of present-day Slovenia, and the remainder in Italy along the Isonzo River on the eastern sector of the Italian Front between June 1915 and November 1917.

Isonzo front
Part of Italian Front (World War I)

Depiction of the Battle of Doberdò.
Date23 May 1915 – 27 October 1917
(2 years, 5 months and 4 days)
  • Five Italian victories
  • Three inconclusive
  • Three Austro-Hungarian victories and final Central Powers victory[1]
 Kingdom of Italy  Austria-Hungary
 German Empire
Units involved
2nd Army
3rd Army
5th Army
Casualties and losses

Italian military plans

In April 1915, in the secret Treaty of London, Italy was promised by the Allies some of the territories of Austro-Hungarian Empire which were mainly inhabited by ethnic Slovenes.

Italian Field Marshal Luigi Cadorna, a staunch proponent of the frontal assault, initially planned breaking onto the Slovenian plateau, taking Ljubljana and threatening Vienna. The area between the northernmost part of the Adriatic Sea and the sources of the Isonzo River thus became the scene of twelve successive battles.

As a result, the Austro-Hungarians were forced to move some of their forces from the Eastern Front and a war in the mountains around the Isonzo River began.[2]


The sixty-mile long Soča River at the time ran entirely inside Austria-Hungary in parallel to the border with Italy, from the Vršič and Predil passes in the Julian Alps to the Adriatic Sea, widening dramatically a few kilometers north of Gorizia, thus opening a narrow corridor between Northern Italy and Central Europe, which goes through the Vipava Valley and the relatively low north-eastern edge of the Karst Plateau to Inner Carniola and Ljubljana. The corridor is also known as the "Ljubljana Gate".

By the autumn of 1915 one mile had been won by Italian troops, and by October 1917 a few Austrian mountains and some square miles of land had changed hands several times. Italian troops did not reach the port of Trieste, the Italian General Luigi Cadorna's initial target, until after the Armistice.[3]

Primary sector for Italian operations

With the rest of the mountainous 400-mile length of the Front being almost everywhere dominated by Austro-Hungarian forces, the Soča (Isonzo) was the only practical area for Italian military operations during the war. The Austrians had fortified the mountains ahead of the Italians' entry into the war on 23 May 1915.

Italian Chief of Staff Luigi Cadorna judged that Italian gains (from Gorizia to Trieste) were most feasible at the coastal plain east of the lower end of the Soča (Isonzo). However he also believed that the Italian army could strike further north and bypass the mountains on either side of the river so as to come at the Austro-Hungarian forces from the rear.

Cadorna had not expected operations in the Isonzo sector to be easy. He was well aware that the river was prone to flooding — and indeed there were record rainfalls during 1914–18.

Further, when attacking further north the Italian army was faced with something of a dilemma: in order to cross the Isonzo safely it needed to neutralise the Austro-Hungarian defenders on the mountains above, yet to neutralise these forces the Italian forces needed first to cross the river — an obstacle that the Italians never succeeded in overcoming.

In the south (along the coastal zone) geographic peculiarities, including an array of ridges and valleys, also gave an advantage to the Austro-Hungarian defenders.


Despite the huge effort and resources poured into the continuing Isonzo struggle, the results were invariably disappointing and without real tactical merit, particularly given the geographical difficulties that were inherent in the campaign.

Cumulative casualties of the numerous battles of the Isonzo were enormous. Half of the entire Italian war death total — some 300,000 of 600,000 — were suffered along the Soča (Isonzo). Austro-Hungarian losses, while by no means as numerous, were nevertheless high at around 200,000 (of an overall total of around 1.2 million casualties).[4]

More than 30,000 casualties were ethnic Slovenes, the majority of them being drafted into the Austro-Hungarian Army, while Slovene civilian inhabitants from the Gorizia and Gradisca region also suffered in many thousands because they were resettled in refugee camps where Slovene refugees were treated as state enemies by Italians, and some thousands died of malnutrition in Italian refugee camps.[5]

Number of battles

With almost continuous combat in the area, the precise number of battles forming the Isonzo campaign is debatable. Some historians have assigned distinct names to a couple of the Isonzo struggles, most notably at Kobarid (Caporetto) in October 1917, which would otherwise form the Twelfth Battle of the Isonzo.

The fact that the battles were always named after the Isonzo River, even in Italy, was considered by some a propaganda success for Austria-Hungary: it highlighted the repeated Italian failure to breach this landmark frontier of the Empire.[6]

The Isonzo campaign comprised the following battles:

Brief summary of Isonzo battles
Battle Dates Italian casualties Austro-Hungarian casualties Outcome
First Battle of the Isonzo 23 June – 7 July 1915 15,000 10,000 Austro-Hungarian victory
Second Battle of the Isonzo 18 July - 3 August 1915 41,800 46,600 Italian victory
Third Battle of the Isonzo 18 October – 3 November 1915 66,998 41,847 Austro-Hungarian victory
Fourth Battle of the Isonzo 10 November – 2 December 1915 49,500 32,100 Austro-Hungarian victory
Fifth Battle of the Isonzo 9–15 March 1916 1,882 1,985 Inconclusive
Sixth Battle of the Isonzo 6 August – 17 August 1916 51,000 42,000 Italian victory
Seventh Battle of the Isonzo 14 September – 18 September 1916 17,000 15,000 Inconclusive
Eighth Battle of the Isonzo 10 October 1916 – 12 October 1916 55,000 38,000 Inconclusive
Ninth Battle of the Isonzo 31 October – 4 November 1916 39,000 33,000 Italian victory
Tenth Battle of the Isonzo 10 May – 8 June 1917 150,000 75,000 Limited Italian advance
Eleventh Battle of the Isonzo 18 August – 12 September 1917 158,000 115,000 Italian victory
Twelfth Battle of the Isonzo 24 October – 19 November 1917 305,000 70,000 Decisive Austro-Hungarian victory; end of the Isonzo Campaign
Total casualties June 1915 – November 1917 950,180 520,532 Central Powers victory, counteroffensives on the Piave river (First and Second battle)

In literature


  1. Palazzo, Albert (2002). Seeking Victory on the Western Front. Lincoln, NB: University of Nebraska Press. p. 111. Retrieved 25 September 2018.
  2. A War in Words, p.147-148, Simon & Schuster, 2003
  3. A War in Words, p.163, Simon & Schuster, 2003 ISBN 0-7432-4831-7
  4. FirstWorldWar.Com The Battles of the Isonzo, 1915-17.
  5. Petra Svoljšak, Slovenski begunci v Italiji med prvo svetovno vojno (Ljubljana 1991).
  6. Isonzo 1917, Sivestri
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