Cao Cao 曹操 sent Jiang Gan 蔣幹, who was a friend of the chief commander of the Wu forces, Zhou Yu 周瑜, to spy on the Wu camp prior to the Battle of Red Cliffs. Zhou Yu immediately understood Jiang Gan’s purpose in paying him a visit and cleverly tricked Jiang Gan and made use of Jiang Gan to get rid of two of Cao Cao’s naval commanders Cai Mao 蔡瑁 and Zhang Yun 張允. However in historical records, Jiang Gan did visit Zhou Yu and attempted to persuade Zhou Yu to defect over to Cao Cao’s service but failed. Zhou Yu did not trick Jiang Gan nor made use of him. There was no evidence to suggest that Cai Mao and Zhang Yun were Cao Cao's naval commanders in the battle either.