Adel's aircraft run on gasoline engines developed in the Power Laboratory, which also has an oil extractor project led by Rudolf Diesel.

In 1892, this historical cow invented the world's first practical diesel-powered compression-ignition engine. This engine has high power, low fuel consumption, and can run on low-quality fuel. Due to financial constraints, it was not until 1897 that a practical four-stroke diesel engine was developed, but he soon went bankrupt and committed suicide in 1913.

Also in Wang Chenhao's trip to Europe, Diesel was also one of them. After being hired by Wang Chenhao's Beiyang Technology, on the basis of Wang Chenhao's strong financial backing, Diesel quickly manufactured a practical four-stroke diesel engine with strong output and fuel economy, but it could not be installed on cars and airplanes due to its large size, but it could be installed on Horan's submarines and Ford's newly designed military trucks.

The output power of the diesel engine is strong, does not pick the fuel, is extremely beneficial for large trucks, and its military value is much better than that of the gasoline engine.

When Diesel's four-stroke diesel engine was successfully developed, Wang Chenhao immediately ordered the next class of commercial submarines studied by Holland and Lake to cancel the gasoline engine and replace it with a diesel engine. The reason for this, Holland and Lake are not very clear, but Wang Chenhao explained the reason to them.

The difference between gasoline engine and diesel engine mainly lies in the compression ratio, ignition method, fuel used and use, the compression ratio refers to the ratio of the maximum volume and the minimum volume of gas in the cylinder when the piston is moving in the cylinder. The larger the compression ratio, the greater the pressure and the higher the temperature. The compression ratio of the gasoline engine is 4~6. The compression ratio of the diesel engine is 15~18. The larger the compression ratio, the higher the efficiency. However, because the cylinder is limited by the strength of the material, and the temperature of the working fluid in the cylinder cannot exceed the ignition point of the fuel, the compression ratio cannot be too large.

They have different ignition methods, gasoline engines mix gasoline vapor sucked into the cylinder with air, pressurize, and then ignite with a spark plug. The diesel engine is automatically ignited by mixing the mist diesel sprayed by the fuel injector with air and pressurizing, and by compression to increase the temperature of the mixed gas. For the military, the safety surname is the first, so the two ignition devices, the diesel engine is more in line with the requirements of the army.

The gasoline engine is small in size, light in weight, easy to start, stable in operation and fast in speed, and is suitable for automobiles, airplanes and other transportation vehicles that require small size and fast speed. The compression ratio of the diesel engine is large, and the cylinder is made more firm and bulky because it has to withstand greater pressure, and is generally made of steel plate, iron plate and other materials. It has high power and is suitable for large trucks, tractors, locomotives and ships with large loads.

Another reason is that submarines for military purposes naturally have to consider the problem of fuel loss, and it is obvious that large transport vehicles generally save money on diesel fuel, and small vehicles save money on gasoline.

Another point is that in terms of power, the diesel engine has higher torque because of the characteristics of low speed, which means that it is more energetic when accelerating, and it is more suitable for load and dragging. However, the disadvantage is that the power is not as high as that of a gasoline engine with a displacement, which is not suitable for high-speed driving. However, it is suitable for military trucks and submarines.

At this time, Tianjin Zhigu Shipyard had already built six Xia-class submarines, namely the Carp (CN-SS-1), the Silver Carp (CN-SS-2), the Grass Carp (CN-SS-3), the Herring (CN-SS-4), the Pomfret (CN-SS-5), and the Danyu (CN-SS-6). The construction of four more submarines was expected to be completed in early 1898.

The first three of the six Xia-class submarines have undergone three months of sea trials and are already in service with the newly formed submarine fleet, although they have been conducting secret training in the waters near the Huludao naval base in the northern part of Bohai Bay. Since the submarine caves at the Huludao Naval Base have not yet been repaired, these submarines can only be temporarily moored at the temporary pier, but they are kept strictly secret so as not to leak information.

In accordance with the concept of the first level of submarine service, the first level of construction, and the first level of design. With the successive commissioning of the Xia-class submarines, the first commercial-class submarine test ship was also launched, and complex sea trials were underway.

Originally, the design standards of the commercial-class submarine had met Wang Chenhao's requirements, but Wang Chenhao temporarily changed the gasoline engine of the commercial-class submarine to a diesel engine, so the mass production of the commercial-class submarine was stopped. After changing to a heavier diesel engine, the merchant-class submarine had to be redesigned and re-tested at sea.

Therefore, at the suggestion of Holland, Wang Chenhao canceled the plan to revise the Shang-class submarine, and classified a Shang-class test boat as a Shang-class submarine, but it was not under construction. As a result, there was only one Shang-class submarine, named the Piranha (CN-SS-11).

Starting with the Zhou-class submarines, the gasoline engine system was abandoned and replaced with a diesel engine system with high safety, high power, low fuel consumption, high torque and strong towing force.

The tonnage of the Zhou-class submarine designed by Holland and Lake also increased to 337 tons and the length to 41 meters due to the increase in the weight and volume of the diesel engine, and the use of four-stroke diesel engines designed by Diesel with two motors and an output of 480 horsepower, which can propel the submarine to sail at a speed of 9 knots underwater, with a surface endurance of 1,200 nautical miles, but the underwater endurance has been increased to 40 nautical miles. The armament is four torpedo tubes with six torpedoes. The armor retains the design of the Shang-class submarine, and the safe diving depth is 61 meters.

The Zhou-class submarine is an improved version of the Shang-class submarine, and on the basis of the Shang-class submarine, the torpedo armament on the boat has been further strengthened. In the design process of the Zhou-class submarine, some shortcomings on the Shang-class submarine were corrected. In addition, two pressure-resistant horizontal partitions are set inside the pressure-resistant hull of the Zhou-class submarine, which divides the boat into a torpedo compartment, a command cabin and a mechanical cabin. This arrangement shows that the Zhou-class submarine already has the basic layout of a modern submarine.

Of course, the biggest feature of the Zhou-class submarine is the use of diesel engines. At that time, submarines around the world used gasoline engines as the main engine, and gasoline engines often exploded, which had a serious impact on the normal operation of submarines and even the performance of their surnames. Under the far-sighted command of Wang Chenhao, China's submarines were the first to use diesel engines and were at the forefront of the world. And the lack of such foresight in the development of submarine hosts by the navies of the world ultimately led to the fact that their submarines began to pay attention only after paying a huge price.

Design displacement (surface / underwater) of Zhou-class submarines: 288t/337t; Main size: 41.1m× 4.2m×3.8m; Main engine: 2 Diesel 4-stroke gasoline engines (for surface navigation), 2 motors (for underwater navigation), double propulsion shafts; Power (surface/underwater): 600 hp/330 hp; Speed (surface/underwater): 13 knots/9.5 knots, endurance: 1179 nautical miles at 9.6 knots on the surface, 40 nautical miles at 3 knots underwater, armament: 4 450mm bow torpedo tubes, 6 torpedoes; Safe diving depth: 61m; Number of crew members: 16.

On December 1, 1897, the Zhou-class submarine began to build a test ship at the Zhigu Shipyard, and it was expected to be completed and launched in March 1898.

Just as the construction of the Zhou-class submarine was begins, the American Expeditionary Force arrived at the San Diego Naval Base in the United States, and after a short rest at the American base, it arrived by train in Tampa, Florida, on the Caribbean coast of the United States, on 17 July, to join the 25,000-strong expeditionary force formed by the US War Department and conduct intense training together.

On the first day of the meeting, the Chinese Expeditionary Force of the Americas won unanimous praise from the officers and men of the US Army for its strict military discipline, clean military appearance, advanced weapons, and well-trained training. At the same time, the Chinese Navy warships Dengyun and Tayun at the Key West Naval Base in the United States also attracted the attention of the Americans, because the second ship, as the most advanced battleship in the world, showed its strong combat effectiveness.

The Americans couldn't help but exclaim, this is the real strength of the Qing Empire.

In the past, in the eyes of Americans, the image of the Qing Empire as groveling and cowardly lasted for more than half a century, especially the fact that the Chinese wore braids was still fresh in their memories. But now they find that the [***] team has no braids and no longer grovels in front of the Americans. Thinking that China and the United States went together to bully the Spaniards, the Americans couldn't help but sigh that China had come out of the dilemma of being bullied and began to take revenge.

Due to the large number of American journalists in the US military bases, the arrival of the Chinese Expeditionary Force in the Americas in the United States was suddenly exposed, which not only caused a sensation in the United States, but also caused an international uproar.

China also organized an expeditionary force, for what purpose? Why did you go to Florida to train with the U.S. military? And who are they targeting? A series of issues are the focus of attention of the great powers.

Soon, the US media took the initiative to expose the intentions of the US War Department, first, the Chinese [***] team successively won the victory in the Qing Russian War and the Ryukyu Restoration War, and the combat effectiveness of the Chinese Army, which has been trained in the German style, has been reborn and has strong combat power, and is called by the German iron-blooded instructors as an army that is no less powerful than the German Army. The U.S. Army needs to learn from the Chinese Army. The second reason is that China's national strength has increased dramatically, and China's political axe has abolished all Spanish privileges in China, and Spain, which has a common enemy with the United States.

The US media soon speculated that the Chinese expeditionary force had arrived in the United States to prepare to attack Spain with the United States, and the US media shouted that the Spanish Army would suffer.

The Spanish political axe suddenly became nervous, and the intention of the two great powers of China and the United States to unite against the Spanish Empire was already very obvious, and the Spanish political axe would face a two-front battle.

The other powers were also surprised, they did not expect that the Qing Empire and the United States had secretly colluded, and there was no suspense about the defeat of Spain at this moment. The great powers immediately began to consider whether to join the division of the Spanish colonies.

Spain's colony of the Philippines has always been the coveted fat of Britain, France and Germany, Britain and France are greedy and do not panic, while Germany is in urgent need of expanding overseas markets, and the newly rising empire wants to attack the old empire and re-divide the colonies.

Britain, France, and Germany immediately sent notes to the United States and the Qing Empire, asking them to meddle in the affairs of the Spanish colonies, but the Qing Empire and the United States immediately denied it, did not admit that they would go to war against Spain, and opposed Britain, France, and Germany interfering in the Spanish colonies.

In the face of the joint opposition of China and the United States, Britain, France and Germany had no choice but to wait, and unless China and the United States declared war on Spain, they had no chance to intervene.

However, Britain, France, and Germany would not wait idly, and they immediately secretly encouraged Spain to support Spain's toughness against China and the United States.

As a result, the Spanish political axe was sick and went to the doctor, listened to the instigation of Britain, France and Germany, and took an unprecedentedly tough attitude towards the Qing Empire and the United States.

On 20 December, the United States Navy blockaded Cuban ports. The warship Northville captured a Spanish merchant ship, and the Qing Imperial Navy's ships Dengyun and Tayun left the U.S. Naval Base in Key West and cruised near the island of Puerto Rico to drive and seize a number of Spanish merchant ships.

This incident immediately angered the Spanish political axe, and on the 21st, the Spanish Empire declared war on the Qing political axe of China and declared war on the United States. On the 22nd, the United States declared war on Spain, and the Qing Empire declared war on Spain.

At this time, the American fleet was mostly concentrated in the Atlantic. The strength of the Atlantic detachment consisted of 5 battleships: USS Iowa, USS Indiana, USS Massachusetts, USS Texas, USS Oregon. In addition, the detachment had two ironclad cruisers: "New York", "Brooklyn" and a number of other small ships.

The Atlantic detachment of the US Navy encircles the island of Cuba and blockades the Caribbean Sea. At the same time, the Qing Imperial Navy's Dengyun and Tayun were also preparing for the Chinese expeditionary force to land in Puerto Rico, surveying the water depth in the waters near Rio Grande in southern Puerto Rico, and finding a suitable landing site in the southeast area of Rio Grande Bay on the 23rd.

On the 24th, Duan Qirui personally represented the strength of a sharp knife battalion of the expeditionary force and landed in Rio Grande Bay. Since it was Christmas in the evening, the nearby Spanish defenders withdrew to the capital city of San Juan to cut down trees to prepare for Christmas, so that Duan Qirui's troops completed the landing without any resistance.

Duan Qirui immediately built a beachhead, but still did not see the Spanish army coming to stop him, so he advanced twenty miles to arrange a defensive line, and then Feng Guozhang led a large army to start landing.

At the same time, the U.S. Army also began to prepare for a landing in Cuba, but because of Christmas, most of the officers and men of the U.S. Army opposed fighting during the Christmas period, so the U.S. War Department postponed the landing operation.

However, George Dewey, commander of the US Asian Squadron in Asia, believed that Wang Chenhao's suggestion to Charles to attack the Spanish army on Christmas Eve was correct.

As a result, Brigadier General Dewey arrived in the South China Sea during the day on the 24th and quietly approached Manila Bay at about 10 p.m. The ships of the U.S. Asian Fleet were loaded with shells, waiting for the Spanish defenders to enter Manila Bay to attack the Spanish Philippine colonial fleet on Christmas Eve.

(To be continued)