Zhao Yanshou
In 946, there were rumors that the major Liao general Zhao Yanshou — who had previously been a major Later Tang general before being captured by the Khitan in the campaign that led to Later Tang's destruction — was planning on defecting to Later Jin. This rumor was believed by Shi's chiefs of staff Li Song and Feng Yu (the brother of Shi's wife Empress Feng). They had Du write a letter to Zhao, encouraging him to do so, with the officer Zhao Xingshi (), who had previously served under Zhao Yanshou, delivering the letter. Zhao Yanshou wrote back (to try to lead Later Jin forces into a trap), stating, "I have long been in a foreign land, and I want to return to China. Please launch a major army to support me, so that I can pull myself out and return with it." Subsequently, under Emperor Taizong's orders, Liao's prefect of Ying Prefecture (瀛州, in modern Cangzhou), Liu Yanzuo (), also offered to defect to Later Jin. Shi thus put Du and Li Shouzhen in command of an army to attack north, with the stated objectives being to first recapture the prefectures Shi Jingtang previously ceded to Liao (the Sixteen Prefectures), and then to destroy Liao. When Du and Li Shouzhen advanced, though, they were met by a large army that Emperor Taizong personally commanded. Du and Li initially intended to withdraw quickly, but Zhang joined forces with them and argued that the Liao army could be defeated, and so they remained in the region for some time. However, the Liao army eventually surrounded the Later Jin army at Zhongdu Bridge (中度橋, in modern Baoding). After Emperor Taizong made the promise to Du to make "him" emperor if he surrendered, Du and Li surrendered their army. Zhang surrendered to Liao as part of this surrender.