As the birthplace and home port of the Japanese Combined Fleet, Sasebo Naval Port is very important as it guards the southern exit of the Tsushima Strait. Surrounded by mountains, the port is protected by the Goto Islands to the west of the entrance channel, and with numerous deep-water berths, it is also a natural harbor. At the outbreak of the German-Russian War, the main force of the Japanese First Fleet was stationed in this military port.

Perhaps it is the sparkle of Sasebo that attracts so much attention that few people pay attention to the Goto Islands, which are located at the westernmost tip of the Kyushu region and are geographically the barrier of Sasebo. Although it is called the Goto Islands, there are actually seven or eight inhabited islands alone, as well as many lesser-populated islands, including Bird Island and the Men's and Women's Islands. As the base of the Goto clan during the Warring States period, the Goto Domain after Tokugawa Ieyasu established the Shogunate period, and the outpost during Toyotomi Hideyoshi's invasion, the Goto Islands have always been strategically important despite their small size. After the Russo-Japanese War, the Japanese Navy successively built a series of alert observation bases here, and with the appearance of submarines as a weapon in the Japanese Navy's combat sequence, secret submarine bases were established on some uninhabited islands in the Goto Islands. These submarines can blockade the Tsushima Strait as close as possible, go to the coastal areas of the Korean Peninsula a little farther away, and operate in the waters of China's Yellow Sea and East China Sea as long as their navigation performance is acceptable.

In February 1928, more than half a year before the outbreak of the German-Russian War, there was constant border friction between Germany and Russia, and people of insight did not regard this friction as an ordinary small dispute, seeing that Germany had maintained a "paid reserve" of 1 million standing troops, 3 million quasi-standing troops and 2 million African colonial troops since 1927, and Russia was also quietly preparing for war. Against this backdrop, a secret submarine base owned by the Japanese Navy and leased by the Russian Navy was built on an isolated island called "Stone Island" by the local residents of the Goto Islands.

As one of the projects of the "Russian-Japanese Mutual Assistance Secret Treaty," the construction of the Shidao submarine base requisitioned more than 8,000 Indians, about 2,000 Malaysians, and more than 3,000 Australian prisoners of war, and dug out a submarine shelter on the south side of the island that can accommodate 50 submarines and thousands of officers and men. These forcibly recruited laborers disappeared out of thin air, and there was generally no news of them, but the sudden increase in the population of a marine fish near Shidao is not difficult to guess.

By the beginning of April, the Shidao submarine base had been stationed with 32 submarines belonging to the Russian Pacific Fleet, about half of which were transferred from the Vladivostok military port, and the other half were received directly by Russian sailors to the base. For certain common purposes, after 1925, Japan sold a total of 79 ships to Russia, a third of which were submarines with a displacement of 700 to 1,050 tons, some of which were said to surpass the Japanese Navy's active submarines in terms of performance.

When Germany declared war on Russia on 4 June, the number of Russian submarines operating at the Shidao submarine base had reached an unprecedented 39, and if it had not been for the fact that the Vladivostok military port had not been blocked by the Germans with a large number of mines on the first day of the war, the Russians would have even sent more submarines here -- in terms of the geographical location of more than 600 nautical miles north of Shidao from Vladivostok and Jiaozhou Bay, it would be possible to blockade Jiaozhou Bay and attack the German merchant shipping routes, and to guard against the German fleet from participating in Shanghai in the north. The presence of the Shidao submarine base undoubtedly significantly strengthened the maritime superiority of the Russian Pacific Fleet.

However. The course of the war situation in the Far East was unexpected, and at the beginning of the war, the German dispatch troops stationed in the Jiaozhou Bay were almost mainly air operations, in the face of long-range minelaying and bombing by the Luftwaffe. The warning role of the Shidao submarine base was not played at all, but the Russian submarine from Shidao quickly completed the first active attack of the Russian Pacific Fleet since the start of the war, and sank a 4,000-ton German merchant ship in the waters of the Yellow Sea in China. Between 7 and 15 June, Russian submarines sank four more German merchant ships, one military transport ship, and one Turkish merchant ship bound for Southeast Asia, and the routes of Germany and its allies in the Far East became a crisis for a time.

"The kind of escort measures of 1924 must be taken!"

In the joint command of the German Far East Dispatch Army in the western suburbs of Qingdao, Feng . Admiral Spee said indignantly that the roar of planes taking off could be heard from time to time outside the window, and not far away was the largest German air base in the Far East, from which bombers would take off every day to bomb Vladivostok and surrounding Russian ports and cities as long as the weather permitted. Compared to the active performance of the Air Force. Spee's fleet has only been active in submarine forces since the beginning of the war, Russian submarines harassing German merchant shipping routes off the coast of China, German submarines doing the same thing in Vladivostok and constantly laying mines on the doorstep of the Russian Pacific Fleet, but the Russians do not have the German minelaying submarines suitable for long-distance navigation and large-scale minelaying.

"That's right! We must change this unfavorable situation, 80% of Qingdao's supplies rely on sea transportation, and if our sea transportation is cut off by the Russians, the consequences will be very terrible! "Major General Ahrens, commander-in-chief of the Army units of the German Far East Dispatch Army, agreed with Spee's proposal, and like Spee. He was also one of the few high-ranking officers who came to Qingdao before 1914 and stayed here for more than ten years, so he was naturally familiar with the situation at the Qingdao base.

At this time, only the commander of the submarine formation of the German Pacific Fleet, Otto. Colonel Helsin's brows were tightly furrowed, and he was quite surprised by the scope and frequency of Russian submarine activities; it stands to reason that Russia does not have a naval base south of the Korean Peninsula, and when Vladivostok is blocked by anchor mines and drifting mines, it is not easier for submarines to get out of the harbor than for surface ships. Judging from the reports of the Air Force's previous bombings, the docks, docks, and material warehouses in Vladivostok were seriously damaged, and even if the ships stationed there were able to leave the port, they would lack sufficient fuel and ammunition to carry out frequent activities.

Immediately after that, the commander of the Far Eastern Dispatch Army, Hermann. Brigadier General Lange & Söhne spoke:

"In terms of the capabilities of our air force, land-based combat reconnaissance aircraft, fighters and dive bombers are capable of attacking Russian submarines operating within 1,000 kilometers of Jiaozhou Bay, but this will greatly increase the consumption of fuel, and if our tankers are threatened, this will inevitably reduce the frequency of bomber sorties! What's more, we can't escort merchant ships outside of the voyage! I wonder if the light aircraft carriers of the fleet can be sent to the route to strengthen the escort forces? ”

Admiral Spee said: "Before the 'Georg' arrives in Qingdao, we can only send a maximum of one light aircraft carrier to patrol the route at a time. Because in the event of an unexpected situation and the main fleet must attack, at least two light aircraft carriers must be dispatched together, otherwise our warships will fight without air cover! ”

The "Georg" is a 40,000-ton heavy aircraft carrier of the same class as the "Ernst", and for strategic reasons, an aircraft carrier battle group centered on it was only deployed in the Mediterranean Sea before the war, and it will only cross the Suez Canal to the Far East after the outbreak of war, and it will not reach Jiaozhou Bay until at least early July, when the strength of the German Pacific Fleet will double. If it weren't for the German-Russian war. Such a maneuver is very likely to arouse strong vigilance and even hostility towards the Japanese Navy.

Spee suddenly turned his head and asked Colonel Hersin, "How about using our submarines against Russian submarines?" ”

Only then did Helsing come back to his senses from his own thoughts, "Submarines vs. submarines? Oh, and overall it won't be better than destroyers or submarine hunters, but sonar will give our submarines a certain advantage! ”

Shi Pei thought for a while, "Well, in this case, we will follow the predetermined plan, the submarine hunter and land-based aircraft are responsible for the waters near Jiaozhou Bay, and each light aircraft carrier plus 4 destroyers, 4 submarine hunters and 1 supply ship will be a mobile formation." 2 destroyers for a mobile detachment. The mobile formation and mobile detachment are responsible for the escort of merchant ships and merchant fleets between Qingdao and Hong Kong-Freeport! ”

After deciding on the anti-submarine strategy of the new land, Major General Ahrens said: "If the government's special envoy and the Nanking Xinming government reach a secret agreement. We may be able to reduce the number of supply ships coming from Southeast Asia, because most of the fuels such as food, ore and coal can be purchased from the Nanking government, so that our factories will continue to produce guns and bullets, and only oil, aerial bombs and heavy equipment will still need to be shipped from China or Africa! ”

"Secret agreement...... "Shi Pei shook his head, "it is better not to prematurely hope for negotiations that are not yet certain, maybe Chinese willing to cede the northeastern provinces in exchange for peace!" I always felt that they seemed to be overly enthusiastic about civil war! ”

"At the moment of external enemies, I think they will still be wise to temporarily stop the civil war, is the internal enemy more important than the external enemy?" Ahrens offers a very different view. However, he seems to ignore different people's views on the importance of civil war and foreign war.

It is well known that some people regard "if you want to go outside, you must first settle inside" as a creed, and at the same time, Ahrens also ignores the urgent need for the so-called "revolutionary" to support foreign forces.

On June 27, 1928, the 12th day after the arrival of the German envoy Hartmann in Nanjing, the talks reached a conclusion in an extremely friendly and harmonious atmosphere, and Chiang Kai-shek, who had rushed back to Nanjing from the camp of the Northern Expeditionary Army, signed a secret agreement with the German government on behalf of the Chinese government, under the premise of maintaining China's sovereignty and independence, the German government would provide the Chinese government with special aid worth 120 million European marks free of charge and provide military instructors to help the squadron improve its combat capability. In exchange, the Nationalist government must give top priority to resisting Japanese aggression, and at the same time supply the German base of Qingdao with food and mineral materials as much as possible, and the lease period of the German team along the Jiaozhou Bay coast will be shortened to 1949, during which the German army can use about 300 square kilometers of land outside the concession area to build the Xindi land defense line, air base, barracks, arsenal and other military facilities.

Soon after, the Nanjing Nationalist Government sent a special envoy to hold talks with Zhang Xueliang, the new commander of the security of the three eastern provinces, and the two sides soon reached an agreement on the timing and method of the change of banners, as well as the conditions for the governance of the three eastern provinces after the change of banners, thus clearing important obstacles for the change of banners in the northeast and the reunification of the north and the south. However, at this time, there were still many veterans and pro-Japanese generals in the Feng army who opposed the change of banner, and the Japanese spies tried every means to sabotage China's reunification, and the Japanese government stepped up its efforts to win over the top level of the Feng army, and the Kwantung Army even suspended the offensive on all fronts, intending to win over the Feng army to continue to maintain the autonomy of the northeast. On the other hand, the Japanese cabinet quietly approved a new plan for military expansion, that is, the formation of four new army divisions in Tokyo, Osaka, Nagoya, and Hiroshima, and the transfer of the long-experienced 13th Sendai Division and the 16th Kyoto Division from Oceania.

One day in early July, under the surface of the South Japan Sea near the Korean Peninsula, a gray submarine was moving slowly at periscope depth.

"The target azimuth, 20 degrees to the east of north, low-speed propellers, it is estimated to be a slow-sailing freighter or merchant ship!"

The sonar soldier wearing an inverted boat-shaped black military cap covered his headphones with one hand, and kept verbally reporting the latest situation to the captain of the submarine.

"Combatants go to their respective positions!"

The captain quickly gave a quasi-combat order, and although there were few Russian merchant ships and freighters sailing in the South Japan Sea, as a submarine commander, he had to be vigilant at all times if he wanted to catch his prey.

It didn't take long for the captain to be able to see the silhouette of the other party through his periscope, and at this moment, he left the periscope gloomily and said, "Lift the alert!" Another damn Japanese ship! ”

Everyone was very discouraged, and a white-faced midshipman lieutenant officer hurried to the periscope, held his hat, and observed it in a good manner. The Japanese ship, which was sailing 3,000 yards away, looked a little bloated, and the striking sunburst flag was hoisted on the mast; because Germany and Japan were still nominally allies, and Japan and Russia had formed a close and private cooperative relationship, the Japanese ships could sail in these waters without any scruples, so the Japanese ship was neither escorted by warships nor took anti-submarine routes, but sailed slowly in the direction of the Yellow Sea.

"Captain, there seem to be a lot of people on that ship, it should be soldiers!" The midshipman said with some surprise.

The captain, who was about to go back to the cabin, turned back and leaned over to the periscope to look, "Well, there are a lot of people on deck, it should be a troop carrier!" Japanese troop carriers! ”

It was true that it was just an ordinary Japanese troop carrier, but in just two weeks, more than 30 such troop carriers continued to travel between Dalian and Japan, and the total strength of the Japanese Kwantung Army quickly increased to 9 divisions and 4 independent brigades, and prepared for the next large-scale offensive from all sides.