1in the autumn of 944, in order to ensure the Nanjing-Shanghai-Hangzhou triangle and prevent American troops from landing in the direction of Zhejiang and Fujian, the Japanese army successively occupied Wenzhou, Fuzhou and other important places and controlled the coastal areas of Zhejiang and Fujian. The Kuomintang troops withdrew westward one after another. The Central Central China Bureau and the Military Department of the New Fourth Army followed the instructions of the Central Committee on developing the anti-Japanese struggle in the southeast coast, developing the Jiangsu-Zhejiang-Anhui border region and the Zhejiang coast to prepare for the strategic counterattack, and ordered 1 division to head south, first to open up the anti-Japanese situation in southern Jiangsu and western Zhejiang, then to get in touch with eastern Zhejiang, and then to develop the camera south. In late February of 1 year, 1 division three regiments crossed the Yangtze River in the south, and in June of 1945, they joined forces with 16 brigade in Changxing, Zhejiang. 13 years 10 months, the Jiangsu and Zhejiang military region of the new fourth army was established, with Su Yu as the commander, Tan Zhenlin as the political commissar (not yet in office), and the troops of southern Jiangsu, eastern Zhejiang and 1 division were reorganized into 1, 2 and 3 columns (the fourth column was added in April), which determined the marching behind enemy lines in the southeast. While the troops of Jiangsu and Zhejiang Military Region are actively advancing behind enemy lines, the Kuomintang die-hards are constantly mobilizing heavy troops in an attempt to annihilate the troops of Jiangsu and Zhejiang Military Region. The troops of the Jiangsu-Zhejiang Military Region were forced to carry out a self-defense counterattack in Tianmu Mountain area for five months.