In the Hongwu period of the early Ming, the grain tax transportation system was divided into northern and southern routes. The former relied on military labor and procurement and the latter on civilian sources. During the Yongle reign of the early fifteenth century, transport along the Grand Canal replaced the previous system of transport by sea. Thereafter civilian roles were increasingly transferred to the military, raising the army's need for vessels to transport the grain. In the Xuande period, this trend was intensified because the direct payment of the grain tax by taxpayers in some areas was replaced by a transmission system in which the army took over responsibility for shipping the tax. It was in this context that a geographically differentiated system for shipbuilding emerged. In Huguang, Zhejiang, and those parts of Zhili south of the Yangzi, military Guards built grain transport ships themselves. In Zhenjiang and the parts of Zhili north of the Yangzi the construction was done by the Qingjiang boatworks. The costs of procurement of materials for both the Guards and the boatworks were allocated in a ratio of 30% to the military and 70% to civilian districts. This system was an important factor shaping boat construction in both the boatworks and the Guards. Underlying the changes in both systems were regional differences in the grain transport system. This variation reflects a breakthrough from the early Ming system.