Some of those who came to join the Perak army were even from the Mongol army. There was a centurion named Zeng Yong in the Mongol Han army of Wang Dechen's department, because he couldn't bear the brutality and bloodshed of the Mongol army, he found an opportunity to bring more than ten of his subordinates to surrender.

Although this Zeng Yong is only a petty officer, he has an extraordinary background. He brought with him an extremely precious military book - "General Essentials of the Martial Arts".

This book is written by his ancestors Zeng Gongliang and Ding Du, famous ministers of the Northern Song Dynasty, because it involves important military affairs, so the number of prints is not much, only for the senior generals of the Song army, and no one in the Perak army has seen this book.

The book analyzes and evaluates the selection and use of troops, education and training, troop formation, marching and camping, ancient and modern formations, communications and reconnaissance, city attack and defense, fire attack and water warfare, weapons and equipment, and many ancient battle examples.

Zeng Yong, a member of the Zeng clan, was ruled by the Jin and Mongols because he lived in Kaifeng Mansion, and he was forcibly conscripted into the Mongol Han army.

Although he was in the camp of the Mongolian army, Zeng Yong never forgot his identity as a Han and always cared about the Han land.

Li Shuang, Cao Ergou, Yu Zhu, and Huang Dagen's high-level officials of the Thunderbolt Army were full of praise for this book, believing that it would be of great effect on the Thunderbolt Army, but they could not deny whether to accept Zeng Yong's subordination.

There are also people in the army who privately talk about Zeng Yong or a spy, after all, the Mongolian army is always full of conspiracies, and its spies are notoriously powerful.

Ouyang Xuan's attitude towards this is that heroes don't ask where they come from, and they use them cautiously after screening. In order for the Perak Army to develop and grow, it must have the courage to embrace all rivers and rivers, and it must not be wasted because of choking on talent recruitment.

By mid-June, the Mongol army had completely expelled the Song army from the western Sichuan Plain, with the exception of the Perak army, and established its rule over the prefectures and counties.

In the course of the attack, the Mongol army also invaded Yokohara Fort and Xinjin Castle many times, but they were easily driven away by the Perak army.

The number of these attacks was only one or two hundred, which was purely harassing, which made the Thunderbolt soldiers led by Cao Ergou quite unhappy, and also made Ouyang Xuan anxious.

The Thunderbolt Army and the Mongols are bound to fight together, and the Mongols can only stabilize their rule over western Sichuan by destroying the Thunderbolt Army, and the Thunderbolt Army can only have a place in Western Sichuan by defeating and crippling the main Mongol force in western Sichuan.

At present, according to the order of Meng Ke Khan, Niu Xuan has led the main force of the Mongolian army to Chongqing Mansion to attack and plunder, and the main force of the Sichuan and Western Mongolian army is only 5,000 cavalry and 10,000 new annexed troops.

The strength of the new annex army was not a cause for concern, but the Mongol cavalry was no match for the Thunderbolts. Only with the help of the fortified city cannon, the Thunderbolt army has a chance of defeating Liu Heima.

Waiting for the Mongols to attack Jiancheng was Ouyang Xuan's strategy of waiting for work. The Mongolian generals stationed in Chengdu were extremely arrogant and wanted to raise troops to destroy the Thunderbolt army in one fell swoop, but Liu Heima, who was in charge of Chengdu's political affairs, was cunning and was not fooled at all.

In his opinion, the Thunderbolt army was poor and hard, and they had powerful firearms, and it was really worth the loss to attack.

Meng Ke Khan's strategy to destroy the Song Dynasty was to first occupy Chongqing Province, then open up the Xiajiang River, and then go down the river to conquer Lin'an, and the first task entrusted to them was to turn the rich western Sichuan Plain into a logistics base for the Mongol army to attack Chongqing Province and other eastern Sichuan.

Before leaving, Niu Lin also told Liu Heima and others that they only needed to hold the city and the plains to block the momentum of the Thunderbolt army's development from the mountains.

In his opinion, the Thunderbolts were just an itch for scabies. Newland's strategy was only half the battle. In his mind, the cavalry is king, and the cavalry's strong mobility can limit the movement of the cavalry, limiting its range of movement to the vicinity of the fortress, and thus trapping the Thunderbolts in the mountains.

But he forgot that the Thunderbolts also had a naval army, and it was still a naval army equipped with artillery. If it is a warship with cold weapons, the Mongolian army can also use crossbow arrows and siege equipment and other weapons to fight against the ships to restrict the activities of the navy.

But compared to high-powered artillery, these weapons are clearly not enough to look at in water warfare. With a cobweb-like river system, the Perak Army's navy was as mobile as the Mongol cavalry in the western Sichuan Plain.

Since the Mongolian army did not come to attack the city and send the heads, then Ouyang Xuan would force them to send the heads with the water army. Due to the fact that they had been making a fortune in silence and keeping it secret, the Mongols did not know the development of the Thunderbolt army, let alone expected that the strength of its naval army would swell to the point where it could threaten itself.

In fact, the Sichuan Ximeng army also had a naval army, and most of these water forces came from the Song army that surrendered under Genting City and Pu Zezhi.

It's just that for these surrendered naval forces, the Mongols were more guarded than trusted, and did not give the necessary equipment and supplies, but gave restrictions and surveillance everywhere.

Even in order to prevent its rebellion, it was not allowed to undertake important military tasks, but was used for guarding and transporting.

Therefore, judging from the books, although the Mongol naval army in western Sichuan has more than 3,000 people and hundreds of ships, its morale is low and its armaments are lax, and it is dispersed and deployed, and its combat strength is really difficult to compare with the naval forces of Jiading Mansion and the Perak Army.

In late June, heavy rains fell for several days in western Sichuan, causing rivers in the plains to swell, and many low-lying areas became waterlogged and even turned into a swamped country.

Taking advantage of the rising waters, the Thunderbolts made a move. When Huang Dagen led four companies of the naval camp to appear on the Jinjiang River outside Chengdu, the Mongols thought it was their own fleet transporting grain.

After the Mongols occupied Chengdu, they sent both land and water armies to attack south along the Jinjiang River, and after successfully taking Pengshan City, they were strongly blocked by Yu Xing's troops in Meizhou and returned with a feather.

Pengshan City is located at the place where the Jinjiang River joins the Minjiang River, and is the throat of the upper reaches of the Minjiang River. After passing through Xinjin City along the Minjiang River, you can reach Chongqing Mansion and Qiongzhou and more than ten counties such as Jiangyuan, Daojiang, Dayi, Pujiang respectively, and you can go directly to Chengdu by tracing the Jinjiang River, and you can reach Meizhou and Jiading Mansion down the river, and the geographical location is extremely important.

Therefore, the Mongolian army defeated Meizhou but did not abandon Pengshan City, but stationed 500 cavalry and 500 sailors here.

Yu Xing repeatedly sent troops to try to recapture Pengshan City but failed, and although his naval army had the upper hand in the water battle, it was repeatedly defeated in the face of cavalry onslaught.

These cavalry are also a huge headache for the current Thunderbolts. It's just that Ouyang Xuan's order was not to capture Pengshan City, but to make a detour to Pengshan City to attack Chengdu, which was not difficult for Huang Dagen to complete this task.

In fact, Xinjin City is only more than 100 miles away from Chengdu City by land, and you need to go south to Pengshan City along the Minjiang River first, and then go north along the Jinjiang River, the distance is close to 300 miles.

The waterway may seem a lot farther away, but it is the quickest and safest route to attack Chengdu. Of course, with the current infantry strength of the Thunderbolt army, if you attack Chengdu by land, you will be defeated by the Mongol cavalry charging or harassing tactics on the way.

In this sneak attack on Chengdu, the Thunderbolt Army and the Navy Army were basically dispatched. In addition to leaving one company and 10 warships in Huangjiadang and Xinjin City, eight companies and 200 warships participated in the operation.

In order to prevent Xinjin City from being attacked after the naval army was dispatched, Ouyang Xuan transferred three companies of the field battalion to Xinjin City to garrison.

When the fleet transporting the field battalion passed by Chongqing Fucheng, the Mongols in the city were panicked, and they knew that Fucheng had long been regarded as a bag by the Thunderbolt army, and they were not in a hurry to seize it.

When Huang Dagen led the naval army through Pengshan City, the defenders in the city did not react much. On the one hand, this city has experienced many attacks by Yu Xingbu, and the defenders have long been accustomed to it.

On the other hand, Huang Dagen only sent ten warships to clear the siege equipment on the city walls during the day to prevent a threat to the Thunderbolt warships, and most of the ships passed through Pengshan City by night.

The Mongol navy in the city had already been frightened by Yu Xing's navy, and was so helpless that they were bombarded by the artillery of the Thunderbolt warships, and they simply cowered in the water village, and even the reconnaissance ships were not dispatched.

After the fleet passed through Pengshan City, Huang Dagen ordered people to hang the flag of the Mongolian army, and sent 20 warships to continue to shell Pengshan City, not only to prevent the Mongolian ships from tailing, but also to prevent the return road from being cut off.