When purchasing submarines, Sun Hao took a fancy to Germany's XXI-class submarines, the Gatto-class submarines of the United States, and the I-400 submarines of Kou State. These submarines have their own advantages, and Sun Hao wants to combine the performance of these submarines.

XXI is a first-class submarine used by the Nazi German Navy in the late World War II, and it is also the world's first submarine designed for underwater warfare, rather than diving for attacking and evading surface ship attacks in the past, and is the prototype of modern submarines. After the war, the submarine development of the Rakshasa country and the United States country was so fast, it was to get the design of this submarine, and even more to get the technicians of this submarine from Germany.

The XXI submarine has a displacement of 1,621 tons on the water, a displacement of 2,100 tons, a draft of 5.3 meters on the water, and an overall length

76.7 meters, 8 meters wide. Hull structure: double-hull structure, power system: 2 seats MANM6V40/46KBB6 cylinder diesel engine, 4000 hp

2-seater SSWGU365/30 electric motor, 5000 hp,

2-seater SSWGV232/28 Jinghang electric motor, 226 hp vane shaft twin axle and double propeller, top speed on water

15.6 knots (diesel), 17.9 knots (electric motor), 17.2 knots (electric motor), 6.1 knots (static electric motor), 15,500 nautical miles / 10 knots (water navigation) 340 nautical miles / 5 knots (submersible) with a crew of 57. Armament, torpedoes, 6 torpedo tubes (23 torpedoes in total), artillery 4 20-mm anti-aircraft guns.

The XXI-class hull is also designed to be simple and streamlined, increasing the speed and reducing the resistance of the submarine, making it more difficult to track and destroy. The interior space and equipment of the XXI class are also larger and better than ever, with large hulls with multiple sets of batteries and still room, as well as refrigeration equipment on board and other shower rooms that are not available on the ship.

In addition, the XXI class also has a special hydraulic torpedo system, which allows the assembly of XXI-class submarines with a very short torpedo time (18 torpedoes can be fired in 20 minutes) and a faster torpedo rate of fire. The XXI class also has a more advanced sonar system, which can be aimed at the torpedo without the need for a periscope, increasing its concealment.

Sun Hao fancy another submarine is the Yi 400 class submarine of Kou State, which is a first-class submarine built by the Kou Navy in World War II, and it is also the largest submarine during World War II, and the largest submarine until the completion of nuclear-powered submarines in the 60s of the 20th century. The I-400 carries enough fuel to circumnavigate the Earth for one and a half cycles, and can also carry three Hariran strike planes and quickly put them into battle.

The main hull of the I-400 class is a transverse twin tube structure, much like a pair of glasses, which is specially designed to ensure the safety of the ship's ammunition depot and huge fuel tanks. The crew compartment at the stern of the ship was restored to a monocular, and this double-barrel design gave it good stability.

There were two torpedo compartments in the bow, each with four 21-inch torpedo tubes in a tandem, with a total of 20 mines. The I-400 class has a dive time of 56 seconds and a draft of 23 feet.

It was designed to dive to a depth of 400 feet, and it was 328 feet during sea trials. Each shaft is connected to a 1,200 hp generator to provide electricity for the submarine's submarine. In actual operation, the submarine reached a maximum speed of 18.7 knots above the surface and 6.5 knots underwater.

With a length of 122 meters and a displacement of 3,550 tons above water and 6,560 tons underwater, the I-400 class was the largest submarine built during World War II. Designed for a maximum speed of 20 knots above water, 7 knots underwater, and a range of 33,000 nautical miles/16 knots, it can last more than four months of combat and can reach any corner of the world.

Armament consisted of a 5.5-inch (140mm) 50-barrel long deck gun at the stern, eight torpedo tubes in the bow, one 25mm anti-aircraft gun in the conning tower, three triple 25mm anti-aircraft guns above the hangar, and three Aichi-made M6A1 Haruran water combat/bombers.

However, Sun Hao felt that the design of the I-400 submarine to carry aircraft was a bit redundant, and the submarine was not an aircraft carrier, so there was no need to use it as an aircraft carrier. Therefore, Sun Hao asked Li Gang to remove this design directly, and asked to install sea-to-air radars on XXI submarines and I-400 submarines.

The I-400 submarine originally also had a radar, but Sun Hao didn't look down on Kou Guo's radar technology. Sun Hao not only asked Li Gang to help the XXI submarine install the sea-to-sea radar, but also modified the firepower of the XXI submarine, removing three of the four 20-mm anti-aircraft guns on the deck and installing a 5.5-inch (140mm) 50-fold long-barrel deck gun.

Submarines can attack not only warships, but also transport ships. The 140mm deck gun on the submarine can be used to attack merchant ships or transport ships, and it is too wasteful to attack merchant ships with torpedoes. At the same time, Sun Hao thought that he might sell these submarines in the future, and such a design could completely increase the firepower of the submarine and make them feel that the firepower of this submarine was powerful.

In fact, the original idea of inventing the submarine aircraft carrier was not the Kou Chinese, but the Germans. Before the invention of radar, the maximum viewing distance that could be reached by the naked eye at sea level was less than 6 miles. For a submarine commander, considering how to detect the enemy situation earlier and conceal himself in time, this is really a big problem. It is for this reason that the concept of combining submarines and airplanes came into being.

In November 1914, the German Navy and Naval Aviation each established their own submarine bases in the Belgian port of Zeebrugge, the latter of which was designed to attack the surface ships of the British with FF.29a seaplanes loaded with 12 kg bombs. Due to the aircraft's limited range, initial attempts to attack were unsuccessful.

At this time, the commander of the U-12 submarine of the German Navy stationed here, Wolter. Walter Forstmann, after consulting with the German naval aviation, came up with a simple and novel idea, which was to load aircraft from submarines and launch an attack in the sea as close as possible to the target of the attack.

On January 6, 1915, a German submarine carrying an FF.29a left the dock and dropped off the surface of the sea less than 15 miles off the coast of Great Britain. The plane took off from the sea and flew straight into the naval port of Kent, England, which surprised the British. The raid was a complete success, and both the submarine and the aircraft returned safely to the port of Zeebrugge.

A completely new weapon was born, the "diving aircraft carrier", and the aircraft on the submarine were mainly used to carry out special operations missions and aerial reconnaissance.

Kou Guo also got the news by accident, and he also invested in the research of submarine aircraft carriers in the early stage of World War II. At the beginning of the Pacific War, the "submarine aircraft carriers" of the Kou Navy were put into actual combat. Since the intelligence agencies of the Mi Army at that time did not know about this, the operation of the aircraft-carrying submarines of the Kou Army achieved a certain success.

In particular, in 1942, the I-25 submarine of the Kouguo Navy used the E14Y1 water reconnaissance aircraft on board to drop incendiary bombs on the home state of Oregon, and the explosion caused a small fire, but it was quickly extinguished by local residents. Submarine-borne aircraft of the Kou Navy even took off from the waters of Australia and the Indian Ocean to conduct aerial reconnaissance of several major cities in Australia and New Zealand. As far as East African waters from Madagascar to Somalia.

However, with the development of anti-submarine technology, radar, and missiles, the brain-opening submarine aircraft carrier eventually disappeared into the long river of history.

Displacement (above/in-water) of the Gato-class submarines of the United States: 1,825 tons/2,410 tons. The total length is 95 meters

Overall width 8.2 m, draft 4.6 m, 4-seater diesel engine with 6,500 hp (4.8 watts), 4-seater electric motor with 2,740 hp (2.0 watt), 2-axle propulsion, maximum speed (water/water): 20.75 knots/8.75 knots

Distance from water: 21,900 km (11,800 nm) / 20.75 knots: 177.6 km (96 nm) / 2 knots. The safe diving depth is 90m, and the crew is 80. Armed with 10 21-inch (533mm) torpedo tubes (6 in the bow and 4 in the stern), 1 3-inch (76mm) gun, and 2 20mm machine guns.

Historically, these three powerful submarines had their own advantages, and the German submarines were the most powerful in combat and had the highest underwater speed. The submarine of the United States does not have much advantage over the submarines of Germany, but when the United States was building the submarine, considering that the submarine officers and soldiers suffered under water, and the design was more humane in various living facilities, the submarine of the United States was the most comfortable. The submarine of the Kou country has the largest range, is large, and carries a lot of ammunition.

These submarines are excellent, and Sun Hao is preparing to place an order for dozens of submarines of each type. Li Gang said that there was no need to build such a submarine, and based on the respective advantages of these submarines, under Li Gang's suggestion, Sun Hao finally decided to build a new submarine by himself, but not by himself, but if the transaction conditions permitted, let Li Gang help him build a new type of submarine. This kind of submarine requires a large range, carries a lot of torpedoes, and is safe and comfortable.

Large ocean-going submarines have a long range and high speed, which is an immutable law. After discussion, the two finally decided to plan to build a submarine with a displacement of not much of the I-400 class submarine.

This submarine is called the submarine ghost class submarine by Sun Hao, it is planned that this submarine is 126 meters long, with a water displacement of about 3,686 tons, an underwater displacement of 6,580 tons, a designed maximum speed of 23 knots on the water, 20 knots underwater, and a range of 35,000 nautical miles / 16 knots, which can last for more than five months, and the combat radius can reach any corner of the world.

Armament consisted of two 5.5-inch (140mm) 50-barrel long-deck guns in the bow and stern, one in the fore and one in the forerunner, and two 25mm anti-aircraft guns in the conning tower. The bow of the boat had six torpedo tubes, carrying 68 533mm torpedoes. The ultimate diving depth is 290 meters, and the safe diving depth is 150 meters. The crew is 128 people, including various arms on the submarine.

However, this is only a planned construction, but Sun Hao believes that the power of science and technology in later generations can build such a powerful submarine under the conditions of the transaction.

At the same time, considering that he only had long-range submarines, Sun Hao ordered an improved XXI submarine to fight together with the large ocean-going submarine he planned to build.

In terms of torpedoes, Sun Hao saw an article about torpedoes in World War II, which was recognized as Kou and Germany, with reliable performance and great power. The torpedoes of Kou were the fastest, and the German torpedoes were stable and had magnetic tracking. The United States once commented on the torpedo of Kou country. If we had this thing, the submarine forces would have a much better record than they do now. German torpedoes were technologically advanced, Japanese torpedoes were highly reliable, and because of the relationship between the Allies, they more or less penetrated each other's design concepts, so each developed a good torpedo

During World War II, there was also a joke about torpedoes: during World War II, a torpedo that did not explode was often inserted into the hull of a merchant ship returning to Hong Kong, just like a whale with a whaling fork inserted into it, which made people tremble.

This is the "secret weapon" developed by the Ordnance Bureau of the United States Navy - MK14 torpedo. Fifteen torpedoes could not sink an oil tanker, and in the first 18 months of the war, the MK14 torpedoes equipped by naval submarines had a dud rate of up to 70%. In this regard, US naval historians could not cry and laugh.

In the late stage of World War II, the torpedo technology of the United States was improved, but compared with the torpedo technology of Germany and Kou, there is still a certain gap.

In the end, Sun Hao's choice of torpedo was a comprehensive torpedo between Germany and Kouguo, and the torpedo technology of both sides was combined to create a new torpedo with more power. With such a mix of technologies, Sun Hao's torpedoes not only have a long range and high speed, but also have magnetic tracking.

Sun Hao believed that using such a torpedo to attack a battleship during the First World War was definitely a matter of hand-to-hand, and it could reach a speed of 45 knots or faster, which was not something that the battleships of this era could avoid.