Nathu La
Starting from 13 August 1967, Chinese troops started digging trenches in Nathu La on the Sikkimese side. Indian troops observed that some of the trenches were "clearly" to the Sikkemese side of the border, and pointed it out to the local Chinese commander Zhang Guohua, who was asked to withdraw from there. Yet, in one instance, the Chinese filled the trenches again and left after adding 8 more loudspeakers to the existing 21. Indian troops decided to stretch a barbed wire along the ridges of Nathu La in order to indicate the boundary.