The Hundred Regiments Offensive (百团大战) (August 20 – December 5, 1940) was a major campaign of the Communist Party of China's Red Army commanded by Peng Dehuai against the Imperial Japanese Army in Central China.
Nevertheless, by 1940 growth was so impressive that Zhu De ordered a coordinated offensive by most of the communist regulars (46 regiments from the 115th Division, 47 from the 129th, and 22 from the 120th) against the Japanese-held cities and the railway lines linking them. From 20 August to 10 September communist forces attacked the railway line that separated the communist base areas, chiefly those from Dezhou to Shijiazhuang in Hebei, Shijiazhuang to Taiyuan in central Shanxi, and Taiyuan to Datong in northern Shanxi. They succeeded in blowing up bridges and tunnels and ripping up track, and went on for the rest of September to attack Japanese garrisons frontally, taking excessive casualties (22,000 regulars, compared to Japanese losses of 3000 or 4000). In all, about six hundred miles of railways were destroyed and the Chingching coal mine, which was important to the Japanese war industry, was rendered inoperative for six months. It was the greatest victory the CCP fought and won during the war. However, from October to December the Japanese responded in force, reasserting control of railway lines and conducting aggressive "mopping up operations" in the rural areas around them.
When General Yasuji Okamura took command of the North China Area Army in the summer, the new approach was "Three All" meaning kill all, burn all, and destroy all in those areas containing communist forces. The population of the communist base areas dropped dramatically and communist operations were severely limited, with CCP forces reduced to 300,000 men. Communist control was also reduced to 10 out of 437 counties in North China. Mao used the subsequent rectification campaign to reassert his personal authority over the party and over military strategy, and this meant the abandonment of any serious communist challenge to the Japanese position in North China for the rest of the war. The Communists would only engage the Japanese in guerrilla tactics and concentrate on rebuilding their own foothold in north China.
Peng was criticized by Mao for revealing the number of the Communist forces to the Kuomintang. Thus the Hundred Regiments Offensive became the last of the two major Communist frontal engagements against the Japanese during the war. During the Cultural Revolution, Peng's action was one of the pretexts used by the Gang of Four that led to his downfall.
It is worth noting that, although the Communists were rarely involved in major upfront combat against the Japanese, the CCP performed many guerrilla actions against them. These battles, involving as many as 10,000 men, are rarely recorded officially in history. Most local CCP commanders simply ordered guerrilla attacks and ambushes as they saw fit, instead of waiting for direct orders from the central command.