Location Sumdorong Chu Valley, Arunachal Pradesh
belli Indian: People's Liberation Army invade into Indian territory in Arunachal Pradesh
Result Indian troops expel PLA from Arunachal Pradesh
Events leading up the near war
After her return to power in 1980 as Prime Minister of India, Indira Gandhi ordered a general review of India's security plans and posture. In 1982-83, she approved a plan submitted by the Chief of the Army Staff, General K.V. Krishna Rao, to upgrade dramatically the sporadic deployment of forces along the Line of Actual Control with China.
Since the late 1960s, India had developed an elaborate plan to defend the Himalayan frontier with China. This involved the provision of screening defences at the Line of Actual Control and the building of strong defence nodes at key points along the frontier. Yet, by the early 1980s, while the forces to man the defences were ready, the nodes were not, and the big weakness was in the fact that the servicing road network had not been built. The decision was now taken to speed up the defence infrastructure construction.
There was another important change. Since 1962, India had not returned to the site of its major defeat-- the Namka Chu an east-west running stream which separates the Thag La and the Hathung La ridge to its south. India's efforts to occupy Thag La was the trigger for the October 1962 Chinese military attack on India. Because there were no other feasible defensive locations north of Tawang, the government had more or less decided that in the event of a new war, they would abandon the town and give battle at the Se La pass to its east. However, after the 1980 review, it was decided that it was important to defend Tawang in a future conflict.  The army made it clear that the only viable line of defence for Tawang would be along the Hathung La ridge. In 1983, an Intelligence Bureau team went to the pasturage of Sumdorong Chu which is somewhat north-east of the confluence of the Namka Chu and Nyamjiang Chu. They stayed through the summer and returned in winter. They did this in the following two years as well. But when they went in 1986, they found that the Chinese had preceded them and set up semi-permanent structures there.
In Feb 1986 the army got a new and dynamic chief, General K. Sundarji, who was determined to press the decisions taken by General Krishna Rao. In addition, Sundarji sought and got government permission to conduct an exercise named "Chequerboard" to see how quickly troops based in the Assam plains could take up their positions on the Sino-Indian border. As part of the exercise, towards the end of the year, the army landed a brigade of troops at Zimithaung, south of Hathung La using its new heavy lift Mi-26 helicopters. These forces went up and occupied the Hathung La, across the Namka Chu from Thag La. All this alarmed the Chinese enormously; they responded with alacrity and moved up their forces to take up positions all along the LAC. At points near this area-- Sulu La, Bum La, etc. the troops were now face to face with their Indian counterparts. This triggered off concerns of Sino-Indian clashes. However, there were no actual skirmishes or clashes.
Possibility of war
At the end of 1986, coincidentally perhaps or otherwise, India granted statehood to Arunachal Pradesh, which is claimed in its entirety by China. The Chinese protested. But the military movements in Tawang, taken in conjunction with this political action was seen as a provocation by the Chinese. In early 1987 Beijing's tone became ominously similar to that of 1962, and with the Indian Army refusing to stand down, Western diplomats predicted war. The result paradoxically was a thaw. Indian Foreign Minister N.D. Tiwari stopped over in Beijing in May 1987 en route to Pyongyang. He carried with him messages from Indian leaders that there was no intention on New Delhi's part to aggravate the situation. The first formal flag meeting to discuss “ the freezing of the situation” since 1962, was held on 05 August 1987 at Bum La in the aftermath of the Wangdung affair.Both sides decided to take up talks with renewed urgency and the following year, Rajiv Gandhi visited Beijing, returning Zhou Enlai's '60s visit. 
The Indian response to the Chinese buildup was Operation Falcon and involved movements across the Sino-Indian border. Among the more interesting deployments, using Mi-26 heavy lift helicopters, was that of Infantry Combat Vehicles (ICVs)and some armour in North Sikkim in the east and Demchok in the west. These two were viewed as particularly threatening by the PLA because they seemed to indicate that India had moved from a strategy of defence in its own territory to that of a larger offensive involving all of southern Tibet.
Both India and China realised the danger of inadvertent conflict and after initial posturing the decided to de-escalate their deployments. The Sumdorong Chu fallout was that India and China decided to restart their dialogue on a new and more urgent basis. After Rajiv Gandhi's September 1988 visit, there was a hiatus of sorts because of political turmoil in India. But finally in 1993, the two countries signed an agreement to ensure peace along the LAC.
The agreement brought in an interesting concept of "mutual and equal" security where thinning of forces was envisaged, based on geographical and logistical considerations. However, its most important element, yet to be implemented, is to have the two sides work out a mutually acceptable Line of Actual Control. As of now the two sides have their own versions of the Line and there are points, especially in the Sikkim-Bhutan-India trijunction, the Sumdorong Chu area and so on where the claim overlap.
陆军参谋长 K.V. Krishna Rao将军提交的大力提升与中国间实际控制线上零散部署的军队的方案。
在1986年2月，活跃的新任参谋长K. Sundarji将军决意推行Krishna Rao将军的决定。此外，Sundarji还获得了政府的许可进行一项
警告了中国人，他们迅速地做出了反应，将部队调动并占据了沿着实际控制线的位置。在附近的一些地点，Sulu La, Bum La中国军