'Operation 5' was the Japanese planned seizure of the Chinese province of Sichuan, which was also known as the 'Sichuan Invasion', 'Sichuan Invasion', 'Chungking Operation' and 'Chungking Campaign', this was a major element of the Imperial Japanese army’s failed plan to destroy the Republic of China during the 2^nd Sino-Japanese War (1937/45).

The undertaking was conceived as a strategic step on the way to the complete Japanese occupation of the Chinese mainland. Consideration of such as operation was started during spring of 1942, after the first phase of mainland operations had been concluded in southern China, and continued into the spring of 1943, and the operation became notorious for the sustained sustained air attacks on cities in western central China.

The core plan was based on the implementation of a multi-front advance on Sichuan from breakthroughs on several axes from northern Shanxi, central Hubei and southern Hunan provinces. The Japanese plan was also based on the use of powerful tactical air support of the Japanese and collaborationist Chinese ground forces and the strategic bombing of Chungking. Further support was to be provided by patrol boats and gunboats of the Imperial Japanese navy on the Yangtze river.

Imperial General Headquarters in Japan ordered the creation of the required reinforcement of 16 infantry divisions and their support and logistical units from reserves within Japan, Manchukuo and the Southern Resources Area (including New Guinea and the Solomon islands group) to supplement the Japanese forces in already operating in the central area of China. The primary assault force for the seizure of Sichuan and the occupation of Chongqing from September 1942 was to comprise 10 divisions advancing to the south-west from the southern part of Shanshi province and six divisions advancing to the west from the area of Yichang in Hubei province. Left-flank support was the task allocated to other divisions currently located in the area of Changde in Hunan province.

The initial phase of 'Operation 5' required that Japanese formations first seize Wanxian, from which they could advance to Chungking on the Yangtze river. To sever the Chinese military lines of retreat and civilian refugee routes, the occupation of northern Fengdu county, in the operation’s centre, was planned, and this could then have been used for the launch of an assault directly on Chengdu or alternatively on Chengdu via Yibin, farther up the Yangtze river from Chungking.

As the operation was planned, the Japanese northern forces had the choice of advancing either toward the southern part of Shaanxi province to capture Siking, or Hanzhong to take Chengdu directly. Alternatively, Japan could have used their limited airborne capability to cut the Chinese lines of retreat and to take the heavily urbanised Chungking area by direct assault.

Both Generalissimo Chiang Kai-shek and some of his senior generals suspected that the intense bombing of Chungking by aircraft of the the Imperial Japanese army and Imperial Japanese navy was designed to support the diversionary Japanese operations against the Chungking area as part of the invasion of Sichuan, and that it was conceivable that the Imperial Japanese army hoped that the terror campaign against Chungking was seen by the Japanese to compel the Chinese to break from the Allies and seek a separate peace with Japan.

According to Major General Chiang Wei-kuo, Chiang Kai-shek’s adoptive son, had their invasion been successful, the Japanese might have intended to establish the puppet regime headed by Wang Jing-wei’s puppet regime in Chungking. The Japanese might also have persuaded Chiang Kai-shek to join Japan’s 'Greater East Asian Co-Prosperity Sphere' and even to aid a future Japanese offensive against the USSR in Siberia and central Asia. Another possibility, Chiang Wei-kuo averred, was the installation of a Japanese civilian or military governor-general to administer the area as an Imperial Japanese army fiefdom in mainland Asia, which could later be expanded to include Tibet and the province of Sinkiang.

However, as a result of opposition to the Imperial Japanese army and Imperial Japanese navy by other members of the Allied alliance, most notably the USA and the British empire, the Sichuan invasion was not received and implemented with any measure of general enthusiasm. In particular, the counteroffensive against Japan in the South-West Pacific and Central Pacific Areas weighed strongly against the possibility of an invasion. Japanese Imperial General Headquarters still favoured 'Operation 5', however, and General Masakazu Kawabe’s China Expeditionary Army used the 1942 plan as the basis for a new plan for the capture of Sichuan: the Battle of West Hubei in May 1943 was part of this new Japanese attempt to reach and take Sichuan.

By this time the Chinese Nationalist forces had the air support of Brigadier General Claire L. Chennault’s American Volunteer Group. In later battles, the Imperial Japanese army suffered defeats at the hands of the Chinese Nationalist armies and, in light of these defeats, the Japanese forces had to abandon all thoughts of a new offensive in this period of the war.

During this time the Chinese Nationalist army despatched seven army officers to Yunnan and thence to India to help in the opening of the land route from India to China whereby the Chinese Nationalist forces could be reinforced and, more importantly, supplied with large quantities of modern weapons and other equipment. In fear of Chinese reinforcements through the cleared route and after sustaining heavy losses in the Battle of Changde, the Imperial Japanese army switched its strategic attentions to Yunnan province with the object of preventing any future Chinese counteroffensives from that area.