李愬
By summer 817, Li Su was formulating the strategy of making a surprise attack on Zhangyi's capital Cai Prefecture with Li You and Li Zhongyi, and he set apart 3,000 elite soldiers, calling them the "Tujiang" (), and trained them for this purpose. After a battle in which he failed in capturing Langshan (朗山, in modern Zhumadian), the Tangsuideng troops were depressed, but Li Su stated happily, "This fits within my plans." However, he could not launch his attack on Cai Prefecture at that time, with heavy rains drenching the land at that time.