While the Strafexpedition was causing alarm in the mountains at the Asiago plateau, the situation on the Isonzo front was apparently calmer. During spring small progress had been achieved around Gorizia, on Mount Sabotino and on Mount San Michele. On this last hill, after the Fifth Battle of the Isonzo, the soldiers of the 9th Army Corps had successfully advanced up to a few metres of the frontline of the Austro-Hungarian troops, building new trenches and safe encampments for missile launchers.
But it was exactly in this zone on Isonzo Karst that the soldiers led by Borojevic made an experiment by means of an attack using one of the many technological innovations of the Great War: chemical bombs. Three thousand cylinders were prepared containing phosgene, a gas consisting of chlorine and phosphor which, once released, would drop their contents on the Italian trenches. On the dawn of 29th June a slight breeze arose that favoured this operation and from the Habsburg positions a thick white pall of smoke arose.
What happened afterwards is reported in the tragic testimony of soldiers and officers who were shocked at the sight that they found at the Italian trenches. Corporal Valentino Righetti (Brescia Battalion) described how he reached the trench during the night and thought that it had been completely abandoned given the complete silence that surrounded the area. To his great surprise he found that all the soldiers were in their place, but were strangely asleep. Towards dawn the corporal made a grim discovery: hundreds of men had died in the space of a few minutes the previous day.
Many of them tried to save themselves by making use of the antigas mask that was part of their equipment but its simple design was unable to counter the effects of phosgene. At that time in fact only the German army had masks that were fully functional as had been demonstrated during the chemical attack against the French troops that took place a year earlier at Ypres. The Hungarian soldiers themselves suffered the consequences of this chemical attack as well: at a certain time the wind changed direction and pushed a part of this cloud towards their trenches and this brought about their poisoning which led to the death of many of them.
In this manner at the dawn of 29th June the divisions on Mount San Michele lost about two thousand soldiers while another five thousand were poisoned. The losses of the Austro-Hungarian troops on the other hand amounted to around 250 dead soldiers and about 1,500 men who were poisoned. These amounts are even more horrifying when it is recalled that no advantage was in fact derived from this operation.
