Operation Chahar

Operation Chahar, known by the Japanese as チャハル作戦 (Operation Quhar) and by the Chinese as the 长城抗战 (Battle of the Great Wall), occurred in August 1937, following the Battle of Beiping-Tianjin at the beginning of the Second Sino-Japanese War.

This was the second attack by the Kwantung Army and the Inner Mongolian Army of Prince Teh Wang on Inner Mongolia after the failure of the Suiyuan Campaign (1936). The Chahar Expeditionary Force was under the direct command of General Hideki Tōjō, the chief of staff of the Kwantung Army. A second force from the Peiping Railway Garrison Force, later the 1st Army under General Kiyoshi Katsuki, was also involved.

Japanese Order of battle
The Chinese forces opposing this invasion of Suiyuan were the Suiyuan Pacification Headquarters under the command of General Yan Xishan. Fu Zuoyi, the governor of Suiyuan, was made commander of the 7th Army Group, and Liu Ju-ming, governor of Chahar, was made its deputy commander, defending Chahar with the 143rd Division and two Brigades. General Tang Enbo was sent by Chiang Kai-shek with the 13th and 17th Corps from the Central Army and made Frontline Commander in Chief. The 1st Cavalry Corps was sent to Chahar under the command of Chiao Cheng-shou, facing the Mongolian forces of Teh Wang.

Chinese Order of battle
Following the loss of Peiking, Tang Enbo's 13th Corps (4th and 89th Divisions) took up positions in depth along the Peiking – Suiyuan Railway at Nankou, and  further to the rear at Juyongguan (Juyong Pass). Gao's 17th Corps stationed its 84th Division at Chihcheng, Yenching, and Lungkuan, covering the flank of the 13th Corps from Japanese forces in Chahar. The 21st Division was deployed in Huailai, on the railroad to the rear of Tang's forces. Zhao Cheng-shou's 1st Cavalry Corps, Liu Ru-ming's 143rd Division, and two Peace Preservation Brigades began an attack on the Mongol forces in northern Chahar.

Battle of Nankou
On August 8 the Japanese 11th Independent Mixed Brigade, commanded by Gen. Shigiyasu Suzuki, began their attack on the left flank of the 13th Corps position at Nankou, but were thwarted after three days by the difficult terrain and the stubborn resistance of the Chinese. A new attack on August 11, supported by tanks and aircraft, took Nankou Station, after which Gen. Suzuki's brigade advanced on Juyong Pass.

That same day, Chiang Kai-shek ordered the activation of the 14th Army Group (10th, 83rd, and 85th Divisions) under Gen. Wei Li-huang. Coming by rail from Yingchia-chuang to Yi Hsien, elements of the 14th Army Group were sent on a ten-day march through the plains west of Peiking in a flanking movement in support of Tang Enbo's forces. The Chinese 1st Army made attacks on the Japanese forces in Lianghsiang and Chaili to distract them, and sent a detachment to Heilung Pass to cover the advance of 14th Army Group. From the dates on a Japanese map of the battle, these forces did not reach the area until September, when it was too late, and clashed with Japanese forces from September 9–17 without achieving its objective.

On August 12, Tang Enbo's army counterattacked, surrounding the Japanese and cutting them off from their supplies and communications. On Aug 14th, Seishirō Itagaki's 5th Division was sent to the relief of the 11th Independent Mixed Brigade at Juyongguan.

On August 16, Itagaki arrived at Nankou and began an enveloping attack on the right flank of 13th Corps, making a five pronged attack at Huanglaoyuan. The 7th Brigade of 4th Division under Shih Chueh was moved to block this maneuver, and reinforcements of Li Hsien-chou's 21st Division and Chu Huai-ping's 94th Division were brought up, engaging in days of heavy fighting. On August 17 General Yan Xishan, Director of the Taiyuan Pacification Headquarters, directed the 7th Army, under Fu Zuoyi, to move its 72nd Division and three brigades by rail from Tatung to Huailai to reinforce Gen. Tang Enbo's forces.

Battle of the Great Wall
Meanwhile in northern Chahar the Chinese 1st Cavalry Corps captured Shangtu, Nanhaochan, Shangyi and Huateh from the puppet Mongolian Army of Prince Teh. Elements of the 143rd Division took Chungli, while its main force reached Changpei. During this Chinese advance the Japanese Chahar Expeditionary Force under Lt. General Hideki Tōjō, composed of the mechanized 1st Independent Mixed Brigade and the 2nd and 15th Mixed Brigades, gathered for a counteroffensive from Changpei to Kalgan.

From August 18-19 the Chahar Expeditionary Force counterattacked from Changpei, and took Shenweitaiko on the Great Wall and the Hanno Dam. The scattered and poorly equipped Chinese forces were unable to stop the Japanese, who now threatened the Peiking – Suiyuan Railway at Kalgan. On August 20 Gen. Fu Zuoyi's 7th Army diverted its 200th and 211th Brigades, which had been moving south by rail to join Gen. Tang Enbo's forces, back to defend Kalgan. Fu's remaining 72nd Division arrived to reinforce Chenpien, and his 7th Separate Brigade was sent to defend the railhead at Huailai.

On August 21, the Japanese forces broke through at the cities of Hengling and Chenpien. Gen. Tang Enbo's forces awaiting reinforcement; but, having suffered over 50% casualties, still defended Huailai, Chuyung Pass, and Yenching. Liu Ju-ming's 143rd Division fell back to defend Kalgan from the advancing Japanese.

On August 23, as Seishirō Itagaki's 5th Division pushed toward Huailai from Chenpien against Ma Yen-shou's 7th Separate Brigade, advance elements of the 14th Army Group arrived on the Japanese flank at Chingpaikou, driving off the Japanese outpost there and contacting the Japanese forces advancing to Chenpien and the front beyond. However, they were delayed in crossing the Yungting River, and their attack was delayed until it was too late to stop the Japanese advance. Due to poor communications they also failed to link up with Gen. Tang En-po's forces during the battle. After 8 days and 8 nights fighting, Itagaki, on August 24, linked up with the Kwantung army's 2nd Independent Mixed Brigade at Xiahuayuan.

Withdrawal
On August 26, Gen. Tang Enbo's forces were ordered to break out toward the Sangchien River while Liu Ju-ming's forces were ordered to withdraw to the far side of the Hsiang-yang River.

On August 29 the Japanese unit, called the Oui Column by the Chinese and the Ohizumi Detachment (大泉支隊) by the Japanese, attacked. According to Hsu Long-hsuen this unit moved south from Tushihkou, and on August 30 attacked Yenching via Chihcheng, but was repulsed by the Chinese 17th Corps. A Japanese map of the campaign shows that the unit moved to Guyuan (沽源) on August 25 and to Xuanhua (宣化) by September 7, cutting the railroad in the rear of Tang's forces and east of Chinese forces along the Great Wall.

According to the Chinese account, after repulsing the Oui Column's attack the Chinese 17th Corps withdrew to join the rest of Tang Enbo's force on the far side of the Sangchien River. Kalgan fell to the Japanese on September 3. After Gen. Fu Zuoyi's 200th and 211th Brigades failed in a counterattack to recapture Kalgan, Fu's forces fell back to the west to defend the railway to Suiyuan at Chaikoupao. This brought and end to Operation Chahar.

According to Time magazine, on September 4 the Japanese-aligned South Chahar Government was set up at Kalgan. After the fall of Kalgan, Chahar's "complete independence" from China was declared by "100 influential persons", headed by Prince Teh, a pro-Japanese Mongolian who had long been the head of the "Inner Mongolia for Inner Mongolians" movement. It was Prince Teh, with his Mongolian levies, who helped the Japanese to take Kalgan. Prince Teh was rewarded for his collaboration with the highest position in this new Japanese puppet state, the Mongol United Autonomous Government.

Notes
 * Ohizumi Detachment (大泉支隊). It was a battalion from 4th Infantry Regiment of 2nd Division under the Kwantung Army. But, its course is different than the Chinese account says. It moved from Guyuan (沽源) to Xuanhua (宣化). See