Wei became able to afford sending Sima Yi to another frontier. In a court debate prior to the campaign, the Wei emperor Cao Rui decided that Sima Yi should lead 40,000 men for the invasion of Liaodong. Some counsellors thought the number was too many, but Cao Rui overruled them, saying: "In this expedition of 4,000 li, mobile troops must be employed, and we must exert our utmost. We should not mind the expense at all." The emperor then asked Sima Yi for his assessment on Gongsun Yuan's possible reactions and how long the campaign should take, Sima Yi responded as thus: When Sima Yi set out from the Wei capital Luoyang, Cao Rui personally saw him off at Luoyang's Ximing Gate (), where he ordered Sima Yi's brother Sima Fu and son Sima Shi, as well as other officials to attend the ceremony. Sima Yi, leading 40,000 infantry and cavalry, was accompanied by sub-commanders such as Niu Jin and Hu Zun (). He would later be joined by Guanqiu Jian's forces in You Province, which included the Xianbei auxiliary led by Mohuba (), ancestor of the Murong clan. Having heard of the new preparations made against him, Gongsun Yuan desperately dispatched an envoy to the Wu court to apologise for his betrayal in 233 and begged for help from Sun Quan. At first, Sun Quan was ready to kill the messenger, but he was persuaded by Yang Dao () to make a display of force and possibly gain advantages if Sima Yi and Gongsun Yuan became deadlocked in war. Cao Rui became concerned about the Wu reinforcements, but the adviser Jiang Ji read through Sun Quan's intentions and cautioned Cao Rui that while Sun Quan would not risk a deep invasion, the Wu fleet would make a shallow incursion into Liaodong if Sima Yi did not defeat Gongsun Yuan quickly enough. The campaign The Wei army led by Sima Yi reached the banks of the Liao River by June 238. Gongsun Yuan responded by sending Bei Yan () and Yang Zuo () with the main Liaodong force to set camp at Liaosui, the site of Guanqiu Jian's defeat. There, the Liaodong encampment stretched some 20 li walled from north to south. The Wei generals wanted to attack Liaosui, but Sima Yi reasoned that attacking the encampment would only wear out the troops; on the other hand, since the bulk