On February 5, 1916, the German Army took full control of Bohemia, and most of the Austro-Hungarian troops stationed in Bohemia were willing to accept the leadership of the Grand Duke of Bohemia and the new government, while some Austrian and Hungarian officers and soldiers were to be sent back to China after the situation calmed down.

On this day, the Kingdom of Bohemia officially declared its independence from the rule of the Austro-Hungarian Empire, and the former Grand Duke of Bohemia ascended the throne as the new King of Bohemia (previously the Austrian Emperor), called Otuka V. Subsequently, the Kingdom of Bohemia signed a German-Polish alliance agreement with Germany, according to which Bohemia became a vassal state of Germany with immediate effect, and Germany was to establish military bases and troops in Bohemia, while ensuring that Bohemia's sovereignty would not be violated by foreign enemies. In non-war times, Bohemia will cooperate closely with Germany in the economy, industry, agriculture, etc.; In wartime, Bohemia had to stand on the same side as Germany as a solid ally.

On the afternoon of 5 February, at the invitation of the Austrian aristocracy, German Foreign Minister Stresemann arrived in Vienna by airship to hold talks with the Austrian nobles headed by Adamas, and the senior officials of the central and Austrian governments of the Austro-Hungarian Empire also attended the talks, but they were placed in an insignificant position.

Under the deterrence of the German army by land and air, the politicians of the Austro-Hungarian Empire began to give in, but the soldiers, especially the generals of Germanic blood, were still doing their best to fight against the strong enemy.

After leaving Vienna in a hurry, Baron Kondra and Admiral Anton and Admiral Haus made a south-west march along the Austrian main railway line, making several major bends along the way, as part of the section had already fallen into German hands, and finally reached Klagenfurt, in the southernmost part of Austria, on the afternoon of 5 February. After this, the two said goodbye to each other, and Condela continued to advance to the southwest, while Anton and House turned to the south.

About 50 kilometers southwest of Klagenfurt was the border of pre-war Italy, which is now under the control of Austria-Hungary, along with much of northern Italy.

At the time of the German invasion, there were still about 1.2 million standing armies in the entire Austro-Hungarian Empire. Among them, the Austrian army had 630,000 troops, which was comparable in number to the German army that invaded Austria. In fact, less than 330,000 of the 630,000 troops remained in Austria, with the remaining 300,000 troops and nearly 200,000 Hungarian troops stationed in northern Italy.

Due to the unusual attitude of the Hungarian government in recent days, the Hungarian troops stationed in Italy refused to obey the command of the Austro-Hungarian generals, and they stockpiled ammunition and food and closed their camps. Condra, as the chief of the Austrian General Staff, had no choice but to order the remaining 300,000 Austrian troops to assemble in Udine in northern Italy. While praying that the damned Italians would not take advantage of this time to make a fuss.

However, the Germans were not fools, and on the first day of the invasion, their envoy in Rome contacted the Italian government. The Germans' demands were simple, as long as the Italians used all means to delay the return of the Austrians, and the rewards were rich, such as returning northern Italy to the Italian government, abolishing the Treaty of Vienna, and allowing Italy to rearmament.

After weighing the costs and benefits a little, the Italians agreed very positively. Thereupon. For three days, riots continued in northern Italy under the control of Austria-Hungary. Several railway lines were blown up, some Austrian barracks were attacked, and more than a dozen Italian partisans annoyed the Austrians on the march. Until Kondra arrived in Udine. The 300,000 Austrian troops had not yet been assembled. In addition to the Hungarian army, only the armies of the Kingdom of Dalmatia, the Duchy of Bukovina, and the Duchy of Salzburg were willing to obey the command of the Austrians, so that Condra had 360,000 troops at his disposal. He was about to face the German 1st Panzer Corps and the 4th and 5th armies that had entered southern Austria, of which the 1st Panzer Corps, led by the famous General Guderian, was known as the elite of the German army.

In this situation, Condra led his assembled forces eastward into Croatia-Slavonia, Austria-Hungary, and ordered the remaining Austrian army to move closer to him, in an attempt to resist the German attack on the eastern shore of the Bay of Venice together with the Austro-Hungarian navy.

In the southernmost part of the Kingdom of Croatia-Slavonia, the largest naval base of the Austro-Hungarian Empire, the military port of Pla, stands at the southeastern exit of the Bay of Venice. Shortly after Baron Condra's arrival in Udine. The Austro-Hungarian Admiral Anton and Haus also returned to this harbor of their own. For Admiral Anton House, it is fortunate that his naval officers and men, although also ethnically complex, were basically recruited by the Austrian Navy, while Hungary has no naval tradition, so its influence in the Austro-Hungarian Navy is relatively small.

Before 1848, Pula was a small fishing village, but after nearly 70 years of construction, it has become the largest military port in the Austro-Hungarian Empire, and one of the best equipped and largest military ports and shipbuilding bases in the entire Mediterranean. The current Pula military port is divided into an inner harbor and an outer harbor. The outer harbor is equipped with a tight anti-submarine network and strong fortresses, and the inner harbor is home to many excellent deep-water berths and large dry docks for the construction and repair of warships.

The Russo-Japanese War of 1904-1905 provided a very good example for navies to study the battle, after the fall of Arthur, known as the first fortress in the Far East, countries began to realize that the old model of harbor fortress defense was outdated, so in the years after the Russo-Japanese War, countries renovated and rebuilt their naval bases, and the Pula military port was no exception. In addition to the addition of larger-calibre, longer-range, inland-capable fortress artillery, the port of Pula was built with a dedicated defensive offensive against land, including batteries, forts, and infantry lines, and the garrison of the fortress was increased to 17,000 men.

Upon his return to the military port of Pula, Admiral Anton and House soon received a telegram from Baron Condra.

On the night of 6 February, when the forward units of the German 1st Panzer Corps crossed the border of the Kingdom of Croatia-Slavonia, Admiral Anton and Haus gave the order for the entire fleet to set sail.

As the signal flag was raised in the harbor under the sailing, the steel hills in the Pula military port began to move slowly, the red and white Austro-Hungarian flags were waving in the wind, the mighty cannons were turning left and right with the turrets, and every sailor's face was full of seriousness, they were not going to parade, but to fight!

The Austro-Hungarian Navy is currently divided into three main fleets, one stationed in the Strait of Gibraltar and one in Taranto, Italy. The last was the home fleet stationed in Pula, the largest of the three. The native fleet, under the direct command of Anton House, had 9 battleships, 9 cruisers, 32 destroyers, 38 torpedo boats, 19 minesweepers, 26 gunboats, 2 seaplane carriers, 16 submarines and 59 transports, which was nearly half the size of the Austro-Hungarian Navy in number and tonnage!

For a time, the mast on the sea was like a forest, and the flag was unfurled.

How could such a grand spectacle escape the eyes of the German submarines, the three German submarines lurking outside the military port of Pula - U213, U226, and U310 - almost immediately spotted the departing fleet, they sent a telegram to the Tunisian base, and at the same time approached the exit of the channel in the dark.

Germany and Austria had not yet formally declared war at this time, and the German High Command had previously ordered the German fleet operating in the Mediterranean region to defend itself against an attack by Austria-Hungary. If the other party does not make a hostile gesture. The decision to attack is based on the orders of the fleet commander.

It would be a shame for the experienced German submarine hunters to miss such an opportunity, but until they received orders from the Mediterranean Fleet Command, their main task was surveillance.

The three German submarines currently on duty near the port of Pula are all U2 medium-sized submarines, and most of the officers and men have served in the Mediterranean region for more than half a year, and many of them are veterans of the last war. Among them, the captain of the U213, Major Fabian Frink, is an excellent submarine commander with more than 100 voyages and a total record of 120,000 tons, and the 41 sailors on his boat have also participated in the blockade of the last British sea transportation line with this submarine.

Although the outside environment is dark and windy, and the U2 submarine is still able to judge the size and orientation of the opponent's surface ship by virtue of its advanced sonar.

The first to sail out of the channel was a fleet of 300-ton offshore gunboats, which had been extremely active during the Italian campaign. Shelling of Italian port facilities to support the army offensive. Usually. The Austro-Hungarian gunboats were armed with 2-3 105 or 152 mm naval guns and 1-2 machine guns as auxiliary weapons, and were very poorly armed. The draft is also shallow and is largely immune to torpedo attacks.

The world knew the strength of the German submarine force, and the Austrians did not dare to wait at all, but they saw that the gunboats began to circle the nearby sea after leaving the port, as if they wanted to interfere with the German submarines' hearing and hearing.

As an ally of Germany during the war, the Austro-Hungarian Navy was relatively familiar with the equipment of the German Navy, and was particularly interested in the two weapons of sonar and depth charges, and had repeatedly asked the German Navy to introduce them. For strategic reasons, the German Navy neither refused nor surrendered in its entirety, but handed over the less technical, more primitive equipment to the Austro-Hungarian Navy. For example, the sonar has a detection range of less than 1 nautical mile, and the depth charge is only half as powerful as the German army.

Even so, after the German invasion of Austria, the German submarine forces roaming the Mediterranean were told that they would face a more dangerous opponent than Britain and France.

At a distance of about 3 nautical miles from the exit of the channel of the Pula military port, Major Frink ordered the submarine engines to be turned off, and at this time the depth indicated on the submarine gauges was 10 meters, the standard periscope depth.

After a while, the sound of the engines of the two German submarines was also inaudible. It seems that their captain is prepared to adopt the same tactic - wait and see.

It was not long before the second group of Austro-Hungarian ships sailed out of the channel, and judging by the sound of the engines, Flink judged that the tonnage of these ships was much larger than that of the gunboats, and that they should be battleships of the cruiser or destroyer class. In fact, it was indeed the first detachment of the Austrians - 2 4000-ton cruisers and 5 1000-ton destroyers.

At this time, most of the people on the U213, except for the sonar soldiers, put their ears to the bulkhead and listened.

Suddenly, the sonar man took off one of his headphones and turned to Major Frink: "There's a warship coming towards us!" ”

"Put away the periscope!"

After the periscope was lowered, Flink stood there without saying a word, and everyone on board remained absolutely silent.

Soon, the humming spiral from above went from a faint to a clear and finally a loud roar.

Destroyers of this era usually have a displacement of less than 2000 tons, and the waterline is generally less than 5 meters, so the U213, with the periscope stowed, is not worried about colliding with the other side. However, there was a high chance that they would miss the telegram from Tunisia. Because the submarine can communicate through radio short waves when navigating on the surface and in a periscope state, but this communication method will not work in the water, because the short wave attenuates too quickly in the water, and it has been attenuated before it reaches the surface, so the transmitting antenna must be stretched out of the water to work normally, and the use of buoy antennas or buoyancy antennas can solve this problem, and the German submarine designers are to connect the antenna to the periscope. In this way, as long as the periscope sticks out of the water, the submarine can send and receive information with the outside world.

However, this method of communication was self-exposed, and the distance of communication was greatly limited, but in 1916 it was very good to be able to achieve this level.

When the warship of the Austro-Hungarian Navy passed overhead, everyone on the U213 submarine maintained a calm expression, in fact, most of them still sweated a little in their hearts.

After the roar, the hum gradually decreased, and eventually faded away.

The crowd had just breathed a sigh of relief, only to hear the sonar soldier say, "It's back!" ”

After two rounds of tossing and turning, the Austrian destroyer finally left.

"The other party is really cautious! It seems that today's battle is not easy to fight! Frink said this, but there was not a hint of frustration in his words. On the contrary, in his opinion, the more cautious the other party is, the more it shows that there are big fish behind!

After this, Frink ordered the periscope to be raised, the light was very weak tonight, the viewing distance at sea was very limited, the small periscope was easy to hide in the undulating waves, but the brightly lit ships of the Austro-Hungarian Navy stood out in the darkness.

As one Austro-Hungarian warship after another sailed out of the channel, more and more warships gathered outside the port of Pula.

A little later, Frink received instructions from Tunisia, and the order was signed by the commander of the Mediterranean Fleet, Admiral Speer:

"According to the secret order of the Imperial High Command, once the main force of the Austro-Hungarian navy is found to be out of port, it is to be closely monitored, and if it is attacked by the other side, or if it finds a good opportunity, it can also carry out the attack! In addition, our submarines in the Adriatic waters have been ordered to come, and if the Austro-Hungarian fleet tries to enter the Mediterranean, it will spare no effort to block it! ”