In spite of experience the Entente was slow in learning not to underestimate the military resourcefulness of the Germans, and Ptain's victories, coupled with the failure of the Germans to react, provoked a jubilation which was not justified. To the German Higher Command the loss of a few square miles at Verdun and the Chemin des Dames was a mere matter of detail compared with the ambitious strategy it now had in mind. Situated as the Germans were between two fronts, they were quicker to grasp the significance of events in the East than were Western Powers; and the collapse of Russia had already inspired Ludendorff with the idea and hopes of a final and victorious offensive on the West in the spring of 1918. It must come soon, or the advent of American armies would make it too late. Even the French and British forces were serious enough, and an obvious preliminary would be to weaken the enemy line in France by a diversion. The Germans knew enough about Italy to be confident that a staggering blow would not be difficult to deal, and that if it were dealt it would compel France and Great Britain to go to the rescue of their distressful ally. Italy had all along been inviting some such blow by her concentration on Trieste, a divergent quest after booty which led away from the enemy's vital parts; for the Adriatic was already closed to the Central Empires by the French and British fleets, and the fall of Trieste, however gratifying it might be to Irredentists--though Trieste had never belonged to Italy or Italian rulers--would have no appreciable effect upon the issue of the war. That quest, moreover, left the Italian flank, upon which its front entirely depended, exposed at Caporetto. It was not, indeed, probable that the Italians would have advanced very far had they set their faces towards Vienna; but if their front had faced in that direction, they would not have provoked the disastrous collapse of their whole campaign in the last week of October 1917. Hitherto Russia had prevented the Central Empires from seizing the opportunity which Italy offered; but the triumph of Bolshevism removed that protection and also supplied the Germans with political means for advancing their military ends. Not a few Italian troops had succumbed to propaganda, and when the crisis came they imitated Russian examples in a way which provoked Cadorna--in a censored message--to speak of their "naked treason."
The valour which other Italian troops had shown during the summer and their success on the Bainsizza plateau had not prepared Italy or her Allies for so great a reversal of fortune in the autumn. The attempt after the fall of Gorizia in August 1916 to force a way to Trieste had been checked by the formidable bastion of Mount Hermada, and in May 1917 Cadorna turned to the other great obstacle to his eastward advance, the Selva di Ternova with its peaks M. San Gabriele and M. San Daniele, which dominated the valley of the Vippacco and the railway to Trieste running along it. But these peaks could not be taken by a frontal attack, and an effort was made to outflank them from the north by seizing the Bainsizza plateau and the Chiapovano valley behind it. A week from 14 May was spent in the preliminary operation of extending the Italian hold over the east bank of the Isonzo above and below Plava, and in seizing the westerly edge of the Bainsizza plateau with its two peaks, M. Kuk and M. Vodice. This advance over difficult country required great endurance and valour, but it fell short of anticipations, and on the 23rd Cadorna struck another blow in the direction of the Hermada. Hudi Log, Jamiano, Flondar, and San Giovanni were captured, and for a moment a footing was gained in Kostanjevica and on the lower slopes of Hermada; but an Austrian counter-attack on 5 June recovered Flondar and drove the Italians off the Hermada.
It was clear that Italy unaided could not achieve even the limited objective of Trieste on which she had set her heart, and in July Cadorna appealed for help to Great Britain and France. The former sent and the latter promised some batteries of artillery, but no infantry could be spared in view of our commitment to the Flanders campaign and of French caution after the failure on the Chemin des Dames; and in August Cadorna resumed his attack alone. It was dictated by political rather than military motives; for there was discontent in Italy which the most rigorous censorship could not conceal, and the reference in the Pope's peace note of August to "useless slaughter" evoked serious echoes in a public mind which found inadequate compensation for the meagre and costly results of the Italian campaign in its splendid advertisement by the Italian Government. Italy needed a victory, and Cadorna achieved enough to keep up the illusion of triumphant progress. The bombardment began on 18 August and the infantry attack on the 19th over an extended front of thirty miles from Lom to the north of the Bainsizza plateau to the Hermada and the shores of the Adriatic. Most of the Bainsizza plateau was overrun, Monte Santo at its southern extremity was captured, and the Italians recovered a footing on the Hermada. A terrific and bloody battle was waged early in September for the key-position at M. San Gabriele, but heavy Austrian reinforcements from Russia prevented the Italians from mastering the crest. On the 5th they were again driven back from the Hermada and San Giovanni, while away in the north they failed to take the heights of Lom. This held up their further advance across the Bainsizza plateau, and its eastern half, containing peaks a thousand feet higher than any the Italians had conquered, remained in Austrian hands. No real progress had been made, the partial occupation of the Bainsizza plateau proved useless, the losses had been tremendous, and at the end of September Cadorna reported that his main operations were at an end. Eleven of the sixteen British batteries were recalled, the French were countermanded, and the ball was left at Ludendorff's feet.
He had begun his preparations in August when Otto von Buelow was transferred from the West to the Italian front and given an army composed of six German and seven Austrian divisions. The control of the campaign was taken over by the German Higher Command, and the troops had been trained in the new tactics which were tried by Von Hutier at Riga in the first week in September and were to be used to more serious purpose at Caporetto in October and on the Western front in 1918. Time was of the essence of Ludendorff's strategy; he could not afford, with the American peril in prospect, to prolong the war by fighting in trenches and merely defending the Hindenburg lines. Nor could he even afford that deliberate method of progress favoured by Haig and Ptain, which consisted in rapid advances on limited fronts to limited objectives, or in snail-like movements over wider areas. The strategy which by intense bombardment drove the enemy back a mile or two at the cost of so devastating the ground as to make one's own advance impossible for weeks, could not achieve a decision within the time at Ludendorff's disposal. Some means must be found of reviving the war of movement and repeating in a more decisive form the German march of August 1914. The bombardment of devastation must therefore be sacrificed in the interests of the pursuing troops, and its place be taken by gas shells; and the enemy line must be broken by the superiority of picked battalions and greater concentration of machine guns and other portable weapons. The line once broken, the advantage must be followed up by a series of fresh divisions passing through and beyond the others like successive waves, maintaining the continuity of the flowing tide. The Eastern front was used as a training ground for these new tactics, which served Ludendorff better than any advance into Russia could have done; and they came as a complete surprise at Caporetto.
That was not, indeed, particularly good terrain for the experiment, and in order to hoodwink the Italians more effectively Von Buelow did not select for his attack any sector indicated by the principal Austrian lines of communication. But these defects of Alpine country were counterbalanced by the weak moral of the troops opposed to him. One symptom of Italian instability had been outbreaks during the summer at Turin in which soldiers had fraternized with the rioters, and the mutinous regiments were sent as a penance to that sector of the front which Von Buelow was well-informed enough to select for his offensive. But the nervousness was general: Italians had never yet met German troops in battle, save perhaps in small encounters with diminutive units in Macedonia, and some consternation was created when, about the middle of October, it was ascertained that there were German divisions on the Italian front; and presently popular imagination magnified Von Buelow's thirteen divisions into the combined weight of the Central Empires, with Mackensen at its head as a bogey-man. That was at least a more acceptable explanation than the real one of the disaster which overtook the Italian Army. But it is impossible to gauge with any exactness the extent or effect of German intrigue and Bolshevist propaganda upon the Italian situation. Bolshevist envoys had been received with open arms at Turin, and Orlando, then Minister of the Interior, had refrained on principle from hampering their activities. More singular was the coincidence of Von Buelow's offensive with a Parliamentary crisis which precipitated the fall of the Boselli Ministry.
The German attack began on 24 October amid rain and snow, which never deterred the Germans, and on this occasion even assisted them by increasing the element of surprise. The infected front of the Second Army between Zaga and Auzza broke with such celerity that by dawn of the 25th Von Buelow's men had crossed the Isonzo, scaled Mount Matajur, 5000 feet high, and were pouring across the Italian frontier; and the gains of twenty-nine months were lost in as many hours. Elsewhere Italian troops fought with splendid determination, and the garrison of M. Nero held out for days and died to a man, while their comrades at Caporetto greeted the enemy with white flags, and reserves withheld their assistance. Gallantry to the left and right availed nothing against poltroonery in the centre: the Bainsizza plateau was lost, and the Third Army on the Carso was in dire peril of being cut off from its retreat. Nothing but retreat, and perhaps not even that, was open to the other armies, with the Second in the centre fleeing like a rabble and Von Buelow threatening the left and right in the rear. On the 27th Cividale, on the 28th Gorizia, and on the 29th Udine, twelve miles within the Italian frontier, fell, and Von Buelow had taken 100,000 prisoners and 700 guns. The Third Army escaped by the skin of its teeth, the excellence of its discipline, and the sacrifice of its rearguards and 500 guns at the crossing of the Tagliamento at Latisana on 1 November. Then the rain came down, and no believer in Jupiter Pluvius as a German god could maintain that that river had been turned into a roaring torrent in the interests of the German pursuit.
The Tagliamento could, however, be easily turned from the north, and the Italian retreat continued across the Livenza and the Piave where Cadorna stood on 10 November. The Adige farther south was considered by many to be Italy's real strategic frontier, but the abandonment of the Piave would surrender Venice to the enemy, and Venice was Italy's one naval base in the northern Adriatic. It must be retained, or the Italian Fleet would have to withdraw to Brindisi and leave the Adriatic and Italy's eastern coast open to incursion from Pola. But if the Piave was to be held, the German threat to turn it by a descent from the Alps down either side of the Brenta valley must be defeated; and it was here that the Caporetto campaign was fought to a standstill in November and December. Fortunately Ludendorff had not been prepared for the magnitude of his own success, and Von Buelow's thirteen divisions had not been cast for the part of destroying the Italian armies. Their object had been twofold, firstly to compel France and Great Britain to weaken their front by sending aid to Italy, and secondly, to secure plunder in the shape of guns, munitions, and corn-growing territory. The Kaiser boasted that his armies had been set up for some time by this Italian success, and Italy's two Allies had no choice but to send divisions to her assistance, the French under Fayolle and the British under Plumer. With that the Germans were content, and although the Austrians continued their efforts to force the Piave and turn its flank down the Brenta valley, Von Buelow's six German divisions took little part in the fighting and were soon with their general sent back to the Western front.
No light task remained for the shattered Italian armies, for the Austrians had been greatly reinvigorated by their success, and continual reinforcements were arriving from the Russian front. Italy had never been a match unaided for her hereditary foes, and the prospect of British and French assistance was needed to stem the torrent of invasion descending from the mountains. The Italians fought well, and politically the nation pulled itself together; but one by one the Austrians captured in November the heights between the Piave and the Brenta which protected the Venetian plain, and it was not until 4 December that the French and British were able to relieve the pressure by taking up their respective quarters on the two cardinal positions of M. Grappa and the Montello. Even so the Austrian advance continued, while a bridgehead was secured across the Piave at Zenson. After a four days' battle on 11-15 December the Austrians reached the limits of their invasion at M. Asolone and M. Tomba on the east, and M. Melago on the west, of the Brenta valley; and before the end of the year the Italians were recovering slopes on M. Asolone and the French those of M. Tomba, while the bridgehead at Zenson was destroyed. Fighting went on well into 1918 without much material change in the situation until Austria was called upon to take her part in the final enemy onslaught in June. Nevertheless the Central Empires had achieved the most brilliant of their strategical triumphs. At slight cost to themselves they had bitten deep into Italian territory, taken a quarter of a million prisoners, 1800 guns, and vast quantities of munitions and stores, and had imposed a greatly increased strain upon the Allies who alone stood between them and victory on that Western front which Ludendorff had selected for the final test of war.