When the army that crossed the team swept towards the battlefield, the city of Gu'an, which had been silent for several days, was also lively again. On the morning of the 19th day of the third lunar month in the sixth year of Xiande (the ninth year of the calendar), seeing that the rain had stopped and the weather had completely cleared, the vanguard of the Northern Expedition of the Zhou Dynasty moved again after being depressed in the camp for several days, preparing to carry out a decisive attack on Gu'an City.

Originally, according to Xu Shao'an's idea, he hoped to delay the attack for two more days, so that the part of the black powder that had been damp due to the continuous rain in the previous days could be dried well by taking advantage of the sunny weather, so as to avoid affecting the effect of the siege due to the quality of the gunpowder. However, at this time, the main force of the Zhou army led by Chai Rong had already arrived in Yongqing County, which was only sixty or seventy miles away from Gu'an, and would arrive at the city of Gu'an in two or three days. If the vanguard force had not taken Gu'an City at that time, then Zhang Zangying, as the chief general of the vanguard force, was afraid that he really would not have the face to meet Chai Rong, who had high hopes for him.

Second, according to the news obtained from Tanma, Xiao Siwen had led more than 60,000 people from the main force of the Youyun Liao Army to leave Youzhou City and rush towards Gu'an City. According to the distance, the other party should have arrived in Liangxiang County at this time, and it is only a hundred miles away from Gu'an. If Xiao Siwen planned to enter Gu'an City before the main force of the Zhou army arrived, or planned to take advantage of the opportunity of the main force of the Zhou army to destroy his lone army, then a distance of 100 miles was not impossible for the Liao army, which was dominated by cavalry, to arrive within one day. At that time, the vanguard troops will fall into the situation of being attacked by the enemy on their backs, and if the main force of the Later Zhou army cannot arrive in time, they are afraid that their own team will be in danger - Xu Shaoan has confidence in his "Shenji Army", and he does not dare to hope that relying on the Liliang of the "Shenji Army" alone can block the attack of the 60,000 Liao army on his camp. Therefore, although he was still a little unsteady in his heart, in the face of this situation, Xu Shaoan had to agree to Zhang Zangying's decision to immediately start attacking the city, and led all the men and horses of the "Shenji Army" to fight, and lined up with other horse infantry troops under the city of Gu'an.

Since Zhang Zangying did not intend to salute first and then soldiers like he did in the last siege, he and Xu Shao'an led the army to Gu'an City and began to deploy their troops according to the siege formation. Swordsmen and shieldmen, flintlock pikemen, and spearmen lined up directly in front of the formation, covering the crossbowmen behind them and the artillerymen who were setting up their artillery. The cavalry units roamed on both flanks of the large array, ready to meet the Khitan cavalry who planned to attack the large array.

With such a big movement of the Zhou army under the city, the Liao army guarding the city had already been reported to the guard general Cao Jiyun. When Cao Jiyun heard this, he hurriedly took his own soldiers to the top of the city and looked at the Zhou army array not far away. Seeing that the Zhou army began to erect artillery as a few days ago, and had the experience of being attacked by artillery last time, Cao Jiyun, who thought that he had discovered the characteristics of artillery attacks, immediately ordered the defenders to follow the previous arrangements for Haode to deal with the method, leaving only a small number of soldiers at the head of the city to monitor the movements of the Zhou army, and most of the Liao army withdrew from the city head and waited in the cave under the city wall to avoid the killing of the Zhou army's artillery. At the same time, Cao Jiyun also sent people to the north to ask for help from Xiao Siwen, who had already entered Liangxiang City, and asked his boss to immediately send troops south for reinforcements. In this way, even if the vanguard of the Zhou army under the city cannot be eliminated, then before the main force of the Later Zhou army arrives, they can at least hold Gu'an - because Yongqing City is too small and not conducive to defense, so if Gu'an is lost, the Liao army's defense line can only shrink to Liangxiang City, which is only a stone's throw away from Youzhou City, and it is by no means the best battlefield for the main forces of the two sides to face off.

Cao Jiyun arranged for his soldiers to hide and ask Xiao Siwen for help, but Zhang Zangying and Xu Shao'an outside the city knew nothing, and they were still urging the gunners and servants to step up their artillery and strive to take Gu'an City before dark. As a general who had never served in the "Shenji Army," Zhang Zangying did not fully understand the advantages and disadvantages of artillery and other firearms, but he did not expect Cao Jiyun to have such wisdom and find the characteristics of artillery bombardment in such a short period of time after suffering only one shelling. As one of the few people who know the performance of firearms best in this era, Xu Shaoan overestimated the deterrent power of the firearms in his hands to the generals of this era, and underestimated the ability of the generals of this era to adapt to factors such as war mode and opponent's weapons and equipment, but he made the mistake of underestimating the enemy - although he had some concerns about Zhang Zangying's order to conduct demonstration shooting in Gu'an City, but his subconscious so-called "superiority of the traverser" made his concerns not last long. was thrown out of the sky in consideration of the face of his boss and the underestimation of the IQ of the ancients. ,

Zhang and Xu were so light on the enemy that they had not even carefully observed the movements of the Liao army defending the city at the head of the city before they even started the shelling, so they naturally had to pay for the adverse consequences arising from this. After most of the formation, all the guns of the vanguard were erected. With Xu Shao'an's order, the herald on the temporary watchtower immediately danced the small flag in his hand, and after a while, dozens of artillery pieces fired almost at the same time, and the huge sound shook the ears of the infantry around him, and it seemed that even the ground shook a few times. Immediately afterwards, the gates, city heads, and even the city walls of the southern city wall of Gu'an City burst out one after another with loud noises, smoke, and even fires.

However, as the shelling continued, Zhang Zangying and Xu Shao'an, who only raised their binoculars to observe the situation at the head of the city after the shelling began, discovered a problem almost at the same time - the number of defenders at the head of the city was extremely small, and at a glance, there were only one or two hundred at most. And this phenomenon made a thought pop up in the minds of the two almost at the same time - the Liao army found a way to avoid the shelling, and did not only know how to stupidly guard the city and be shelled like last time. This discovery surprised Zhang and Xu a little, especially Xu Shao'an, while carefully observing the situation in the city, he secretly complained in his heart that he was too big, too underestimated the IQ of the ancients, and too much believed that these firearms in his hands were actually only equivalent to primitive entry-level firearms. Now the Liao defenders have found a way to avoid artillery bombardment, but they are afraid that the next siege battle will take some more twists and turns.

However, although the shelling did not cause heavy casualties to the Liao army as expected, Xu Shaoan and Zhang Zangying were slightly relieved that under the continuous bombardment of the nine-jin cannon and the twelve-jin cannon, a section of the city wall on the west side of the southern city of Gu'an was not only shattered by the solid cannonballs, but even the rammed earth exposed inside had begun to loosen and showed signs of collapse. At the same time, the southern gate of Gu'an was completely shattered by shells, revealing the bags of masonry and earth used to block the gate. Therefore, after a brief moment of surprise at the flexibility of the Liao army's guards, Zhang Zangying regained his self-confidence. While observing the crumbling city wall, he said to Xu Shao'an: "I didn't expect that this Cao Jiyun is also a little really capable, and he can actually come up with a way to remove the soldiers defending the city from the city head to avoid the shelling of our army." It's just that his little trick can be avoided for a while, but he can't hide for a lifetime. Seeing that the western wall of the city has been loosened, if the siege powder cartridge is fired at the damaged area with a ballista, or if the brave soldiers are simply sent to carry the powder cartridge directly to detonate it, the collapse of this section of the city wall will only be a matter of moments. If you can't do it, you can also send a cart to transport the gunpowder bag under the city wall and blow it down. ——The siege powder cartridge is a weapon created by the Zhou State Military Weapons Supervisor under the guidance of Xu Shao'an. This weapon is based on a straight and sturdy bamboo tube with a bowl mouth, with an iron tip on the front and tail feathers at the back, which is fired by a ballista or a large bed crossbow - if necessary, it can also be nailed into the city wall or barracks wall by hand - after it penetrates deeply into the enemy's wall or barracks parapet, the explosion of black powder filled in the bamboo barrel is used to loosen and eventually collapse the city wall, opening a breakthrough for infantry attacks.

Although he blamed himself for his previous underestimating enemies, for Xu Shaoan, what Zhang Zangying said was also reasonable. Therefore, he nodded and replied, "What Lord Zhang said is very true, although Cao Jiyun escaped the artillery bombardment, it will take more time for his men and horses to come out of hiding to defend the city. When our army blew down the city wall with siege powder canisters and the foot soldiers began to climb to the top of the city along the ruins of the city wall, it was difficult to say whether the Khitan troops hiding outside the city wall could go to the city in time to intercept them. ”

With Xu Shaoan's approval, Zhang Zangying was more confident. As soon as he discussed with Xu Shao'an, he decided to stop the shelling and attack the city with all his might. So, after about half an hour of continuous bombardment, the entire artillery array gradually fell silent. With the end of the shelling, most of the flintlock pikemen, sword and shield soldiers, as well as some pikemen and cavalry, broke away from the army formation, carrying various siege equipment, and swooped towards the southern wall of Gu'an City.