The Austro-Hungarian Navy in late WWI had suffered a consistent decline and severe setbacks. Since 1917, the Allies had begun to use large convoys in the Mediterranean and the Adriatic in order to maintain their supplies to the Middle East, as well as to Italy and the Salonika front, in a similar way as in the Atlantic. While escorting these convoys took up a large capacity of the naval forces, the effort was worth it. Following the entry into the war by the USA, American destroyers were incorporated into these escort operations, alongside the British, French and Italian naval forces. However, the Allies were aware that this protection was only a conditional one and that, ultimately, it came down to hitting the German and Austro-Hungarian surface and submarine vessels in such a damaging way that the threat to Allied shipping would be reduced. Attempts were made at improving the fight against the naval forces of the Central Powers in that – in the second half of 1917 in particular – everything possible was done in order to precisely monitor the radio traffic and to decipher the code words whenever expedient.
Germans, Austrians and Hungarians had long ago become dissatisfied with the development of the naval war in the Mediterranean, despite sporadic successes. German statisticians had calculated that the tonnage figures of the ships sunk by the submarines were decreasing constantly per boat and per day. Even the numbers of Austro-Hungarian sinkings since the autumn of 1917 alone were cause for concern. In October 1917, an outstanding 12,000 tons of shipping space had still been destroyed, but in November only 4,000, and in December 1917 not a single sinking. The Germans were also becoming increasingly concerned due to the Allied aerial threat to Pula (Pola) and Kotor.
On 12 November 1917, Kaiser Wilhelm had visited Pula and had made a vain attempt to convince the Commander of the Fleet, Admiral Njegovan, to decommission the capital ships and to use the crew for other purposes. The visit by Kaiser Wilhelm took place at a time when the breakthrough Battle of Flitsch-Tolmein had been fought, and Austro-Hungarian and German troops had crossed the Tagliamento River and advanced to the Piave.
For the Allied fleet presence in the Mediterranean, this naturally did not remain without consequences. Italy had requested additional support from its allies, and wanted it to be transported across the sea in particular. The first to react were the British, who had two monitors enter the lagoons of Venice. However, Italy had also requested that Japan send additional destroyers. This request could not be met, while instead, the British and French gave the Italians the good advice of using their own naval forces more actively. British destroyers spent 70 per cent of their time at sea, while the Italians lay in the ports for a larger proportion of the time. However, the Entente powers had naturally understood Italy’s concern that the Austro-Hungarian troops might perhaps still wish to expand on the successes of the Twelfth Battle of the Isonzo by landing in the Rimini area, or attacking Venice. The Allies were also concerned that Italy might be forced to withdraw from Albania. If Italy were to retire from the war, it was even considered how the Allies might take possession of the Italian fleet. But all these worries had been groundless.
The situation in Italy had continued to occupy the minds of the Allies. At a naval war conference at the end of November and the beginning of December 1917, the Italian Prime Minister Orlando pointed out that the Italian armaments industry could no longer function due to a lack of coal, and hoped that additional coal supplies from the Allied marines of at least 100,000 tons could be provided. The British and French were not in a position to fulfill the Italian requests, but they could do nothing else but assume additional tasks in the leadership of the naval war, transport more supplies across the sea and protect the convoys as best they could. Here, the Imperial and Royal Navy no longer appeared to represent a significant danger.
The activities of the Fleet continued to be reduced. Like the land army, the crews on the ships and the entire naval personnel were forced to acknowledge that the hardships were now being felt everywhere, and that the shortages caused significant limitations. In the short term, a measure appeared to take effect that had in fact seemed obvious: Vice Admiral Richard von Barry organised a fishing fleet of 650 boats and 4,500 sea men, most of them former fishermen, who were to provide additional food supplies. However, ultimately, this was also not the solution. Morale continued to sink, and lethal boredom became rife. In 1916, the Naval District Commander of Trieste, Vice Admiral Alfred von Koudelka, suggested deploying the sailors with the land army according to a type of rotation principle. This would surely stave off the boredom. He then received the inmates of the naval prison in Pula, who did indeed serve at the front, but who after completing their sentences returned to their ships. The experiment was not repeated.
Aside from more minor activities, Njegovan failed to disrupt the Allied fleets in the Adriatic. Neither were connections interrupted, nor were there larger naval battles com parable to the one in the Strait of Otranto, for example. With the sinking of the Wien, however, the calamity had already begun to descend upon the Imperial and Royal Navy. Next came the mutiny in Kotor, then Njegovan was dismissed and replaced by Rear Admiral Miklos von Horthy. His nomination as Commander of the Fleet was accompanied by a full shake-up of the command authorities in Vienna, new appointments and reassignment of posts. Horthy began to prepare the Fleet for action, even if it was not aimed at achieving much more than keeping the people busy, and thus counteracting at least one reason for the mutiny. And when, in May, another mutiny occurred on a torpedo boat in Pula, Horthy decided to make an example of those involved, and had the two ringleaders, a Czech and a Croat, shot as a public warning. Twenty men from each ship lying in Pula were required to attend the execution.
Clearly, the measure had an effect, since until the autumn the Commander of the Fleet no longer had substantial cause for concern with regard to the discipline of his ships’ crews. However, this altered nothing when it came to the lack of activity of the Fleet. Older ships were taken out of service and disarmed. Particular attention was paid to Kotor, where there had been fears of an Allied attack since the autumn of 1917. In April 1918, Emperor Karl asked Horthy whether an Austrian submarine might be sent to the Black Sea. Horthy refused; he referred not least to the fact that the Austro-Hungarian flag was already present in the Black Sea, since the Danube Flotilla units had arrived there.
In the spring of 1918, the naval war in the Adriatic had begun to take on other forms. Italians and Austrians attempted to cause damage through small forays, landing operations and penetration into the naval ports. The Allied measures for protecting their shipping, particularly the convoy system and the intensification of the fight against submarines, were taking effect. In January 1918, the Germans lost more submarines in the Mediterranean than throughout the entire year of 1917. In May 1918, German submarine losses in the Mediterranean again increased sharply. The British intensified their air attacks on Kotor, which had a greater effect than the British themselves were aware. The necessity of taking protective measures, and only being able to depart and come in to port under highly specific conditions had an enormous deceleration effect on the naval warfare and also obstructed the submarines in particular.
In this situation, Rear Admiral Horthy wanted to repeat his raid on the Otranto barrier. This time, however, not only a relatively small squadron was to take part, but also the 1st Battleship Division. The campaign was planned for 11 June. On the evening of 8 June, the first battleship group, with two ‘Tegetthoff’ class ships, left Pula. Horthy himself travelled on the flagship of the Fleet, the Viribus Unitis. The second group of battleships, with Szent Istvan and Tegetthoff, left Pula on the evening of 9 June. However, the Allies had been warned. The increase in radio traffic and aviation activity had drawn their attention to the fact that an operation was being planned. Even before dawn on 10 June, Italian torpedo boats (MAS = Motoscafi Antisomergibile) fired two torpedoes at the Szent Istvan. The battleship was so severely hit that it sank in less than three hours. Then Horthy abandoned the operation, since the element of surprise had without doubt been lost. Thus, the final turning point in the naval war had been only too obvious. Of less significance was the fact that the Americans had also sent a submarine fighter unit to the Mediterranean, in order to participate in the blockade of the Strait of Otranto. The ships, the majority of which were manned by volunteers and crews who had no experience of naval war at all, were now no more than an outward extension of the Allied presence. Until the end of the war, they failed to sink even a single submarine.
Following the failure of the Piave Offensive, the situation also deteriorated week by week, indeed almost daily, for the Imperial and Royal Navy. The transport of supplies by sea for the Imperial and Royal XIX Corps, which was then renamed `Army Group Albania’, was already very highly at risk. No other supply and evacuation opportunities were available. Loyalty among the troops was diminishing continuously. The submarines were achieving almost no further successes. The Germans were now nowhere near being able to make good the loss of the Austro-Hungarian vessels, and an increase in their number to 28 in total in the Mediterranean in August 1918 (including the submarine UB 128 under the command of Lieutenant Wilhelm Canaris) remained without impact, since the number of vessels that were suitable for action was decreasing steadily. Horthy described the Fleet as still ready for service, and also claimed that the consequences of the revolt in Kotor had been overcome. However, he pointed out that the continuous escorts provided for the convoys sailing up and down the Adriatic coast, which were attempting to reach Albania in particular, were making extremely high demands on the torpedo boat flotilla. Since the construction of fourteen submarines and nine torpedo boats had been ordered, and that it could still not be predicted when they could be put into service, the collapse of the Fleet within a foreseeable period of time appeared to be inevitable. On 17 October, the Army High Command ordered the Austro-Hungarian submarines to end the commercial warfare and instructed them to restrict themselves from then on to standing ready to defend the Dalmatian ports. At this time, the Allied fleet formations were already more or less sailing freely in the waters of the Mediterranean. They even used their battleships to attack the Albanian coast and to block the Austrian ports. The last major operation conducted by the Imperial and Royal naval forces was to fire at the port of Durazzo on 2 October, which, while having no significant effect on the port itself, gave an Imperial and Royal submarine under Ship-of-the-Line Lieutenant Hermann Rigele the opportunity to torpedo a British cruiser. Thus, the end had also come for the Imperial and Royal Navy.