Deyu's questioning, argued that because neither Chen nor Zhang Jiang was from the Lulong army, the Lulong soldiers did not completely support either, while Zhang Zhongwu was well-supported by the Lulong soldiers due to his father's long-standing career in the Lulong army. Wu opined that when Zhang attacked Fanyang, he would be quickly able to capture it due to the soldiers' support — and even if he failed to do so, because the food supplies for You Prefecture (幽州, i.e., Fanyang) came from the prefectures and bases to its north, Zhang Zhongwu could starve You Prefecture into submission by cutting off its supply lines. (According to Wu, Zhang Zhongwu was, at time of the petition, in his 50s, but Wu did not state which year Zhang Zhongwu was born.) Li Deyu opined that, whereas Chen and Zhang Jiang were supported by the soldiers and then requested imperial commission, and Zhang Zhongwu requested imperial commission first, it would be proper to commission Zhang Zhongwu. Emperor Wuzong agreed, and commissioned Zhang Zhongwu as the acting governor. Zhang Zhongwu was soon able to capture You Prefecture and take over the circuit. Emperor Wuzong had his granduncle Li Hong () the Prince of Fu nominally named the military governor of Lulong and commissioned Zhang Zhongwu as the deputy military governor, and created Zhang Zhongwu the Prince of Lanling or the Duke of Lanling. In spring 842, Emperor Wuzong made Zhang Zhongwu the military governor. As military governor Campaign against the Huigu At the time that Zhang Zhongwu took over Lulong Circuit, Lulong, along with other circuits on Tang's northern border, facing the threat of Huigu raiders, who had headed south in the aftermaths of the Huigu Khanate's collapse due to Xiajiasi attacks. The Huigu splintered into many groups, and in 842, the noble Najiachuo () advanced on Xiongwu Base, threatening You Prefecture. Zhang Zhongwu sent his brother Zhang Zhongzhi () with 30,000 soldiers to engage Najiachuo. Zhang Zhongzhi defeated Najiachuo, killed many Huigu, and accepted the surrender of some 7,000 tents of people, who were subsequently distributed to the various circuits. Najiachuo fled, but was captured and killed by the leader of another Huigu group, Wujie Khan. Meanwhile, Zhang also sent his officer Shi Gongxu () to the Khitan and Xi tribes to kill the Huigu emissaries to those tribes. Further, when he defeated Najiachuo, he took, as hostages, a group of Shiwei chieftains