After the Italian success in June, 1915, certain readjustments were manifest in the Austrian forces in the Italian theatre. Although there was no declaration of war between Italy and Germany, it was reported that German officers were sent to aid the Austrians, and that the forces of Archduke Eugene were progressively strengthened from this time on. German soldiers who joined the Austrian detachments were supposed to have volunteered in an irregular individual manner. In this manner Germany preserved the appearance of neutrality.
The latter part of June, 1915, found Austria occupied with the siege of Lemberg, and the archduke, apparently, was content to hold his own on the Italian front until a decision had been obtained in the more important operations against the Russians. Satisfied with their initial successes, General Cadorna on land and the Duke of Abruzzi at sea settled down to a slow, patient chess play, not unlike that worked out by General Joffre in France. Cadorna issued a statement to the Italian people in which he warned them that the preliminary successes which, he said, had made good the strategical defects of their frontier, would be followed by a long stage of gradual approaches against the enemy's second line.
The attrition of the Austro-Hungarian forces would be carried on by long-range artillery and sappers and local trench warfare with hand grenades. The Italian commander in chief resolutely refused to divert any part of his forces to the Dardanelles. Possible danger to Italian dominion in Tripoli, pointed out by the leaders of the Entente Powers, did not change his purpose to maintain a single concentrated front and not diffuse his efforts. The war with Austria, he believed, would be won or lost on the Italian frontier. His theory as to the best way to meet advances by the Teutonic allies in new fields was to increase pressure on their home frontiers where their interests were most vital. The Italian army in the field was increased to a million men, and, after the fall of Lemberg, Austria gradually moved more and more troops to the Alpine passes and the Isonzo, until by August she had 600,000 men facing the Italians, double the number arrayed on this front when Italy declared war. Had the Russians been able to hold out longer in Galicia, there is little doubt that Cadorna would have had something to show for the month of July besides a few local victories which did not vitally affect the main campaign.
Italian Attack on Austria.
On June 9, 1915, the capture of Gradisca completed the Italian control of the lower Isonzo, and Cadorna prepared for a general attack on all the strongholds guarding Trieste. Of these the most important were the Carso tableland on the south, Gorizia barring the river-valley of the Vipacco between the Carso and the foothills of the Julian Alps, the fortified system of heights north of Gorizia surrounding the town of Tolmino, and the great intrenched camp of Tarvis above Tolmino extending to Malborghetto and the other Alps of Carinthia. These fortified points had to be attacked generally or not at all. Any attempt to mass an army against any one of them would have spelled disaster, for the Italians would have been flanked by Austrian forces from the north or south. A properly defined advance against Trieste called for a simultaneous thrust at Tolmino and the Tarvis fortress commanding the road to Vienna. The Austrians had been strengthening Tarvis ever since 1859, after Napoleon III overthrew the Austrians in the battles that freed Lombardy. The Austrian fortresses were again strengthened after the siege of Port Arthur had demonstrated the power of high-explosive shells, and again in 1910 when the Teutonic allies made their great discovery that their new giant howitzers laughed at modern defense works of steel and concrete. In remodeling her Alpine strongholds Austria selected positions on the plateau for systems of earthworks containing mobile siege guns.
The key to this immensely strong Austrian line of defense was the railway town of Plava on the eastern bank of the Isonzo under the wooded heights of the Ternovane Forest. Plava was in a salient occupying about the middle of the Austrian line.
Here, on the night of June 17, 1915, the Italians began their general offensive by an attack from Mount Korada on the opposite side of the river. Under cover of darkness the Italian sappers built a pontoon bridge, and the Bersaglieri crossed and carried the town and the surrounding heights at the point of the bayonet. The Austrians realized the importance of the position and quickly returned to a violent counterattack. The Italians threw all their available men into the gap, and a great battle raged on the edge of the highlands east of the river. The Austrians had the advantage of position, for their forces could be massed in the woodland out of sight of the Italian aviators. But, on the other hand, the Italian batteries on Mount Korada were able to pour a plunging fire into the lower tableland; and due mainly to the aid of their artillery the Italian troops drove back the enemy and maintained the ground won by the first dash.
General Cadorna was now in a position to begin a direct attack upon Gorizia. He assailed the Hill of Podgora, forming the barbican of the city's system of defenses and advanced a reconnoitering force toward Mount Fortin. Meanwhile he massed 500 pieces of artillery on the heights commanding the city. But the defenses of Gorizia had been well planned, and they proved their completeness by a long resistance covering a period that brought successive reports that the fortress had fallen. All these reports proved false. South of the city the Austrian intrenchments covered a front of more than ten miles, from the Mount of San Gabriele below Plava to Mount San Michele on the Carso tableland. The trenches were built in the most modern style, of concrete more than a yard thick covered with steel armor, against which ordinary shrapnel had no more effect than so much hail, and even high-explosive shells of medium power did little damage. The Italian weapons of attack were hand grenades and short knives, in the use of which the infantry were expert. Four army corps operating under the Duke of Aosta between Gorizia and the sea were beaten back by the Austrians with heavy losses. This victory so encouraged the archduke and chief lieutenant, General Boroevics, that they decided upon a counteroffensive in force. Therefore, as soon as the Italian attack slackened, the main Austrian army advanced across the Carso Plateau.