The 1987 Sino-Indian skirmish was the third military conflict between the Chinese army and Indian army that occurred at Sumdorong Chu Valley,By the early 1980s, while the forces to man the defences were ready, the nodes were not, and the greatest weakness was in the fact that the servicing road network had not been built. The decision was taken to resume the defence infrastructure construction.India's efforts to occupy Thag La was the casus belli 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 prepare for battle at the Se La pass to its east. However, after the 1980 review, it was decided by the military strategists that it was important to defend Tawang in a future conflict,The defence forces stayed through the summer and returned in winter. This procedure was followed for two years. In 1986, Indian forces found that the Chinese had preceded them and set up semi-permanent structures there.In Feb 1986 the army nominated a new chief, General K. Sundarji, who was determined to press the decisions taken by General Krishna Rao. In addition, Sundarji sought government permission to conduct an exercise named Operation Cheaquerboard 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 The exercise involved 10 divisions and several the IAF and a redeployment of troops at several places in North East India. The Indian Army moved 3 divisions to positions around Wangdung, where they were supplied and maintained solely by air. These troop reinforcements were over and above the 50,000 troops already present across Arunachal Pradesh. These forces occupied the Hathung La, across the Namka Chu from Thag La. All this alarmed the Chinese forces in the region; 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. Due to this action Their is a 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 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 claims are disputed.