Gorge North of Himalaya, the Yarlung Tsangpo River flows east through the Tibetan Plateau and then turns south into a series of massive gorges in Himalayan mountains. Until the 1880s it was unknown by which route it eventually reached the sea or even whether it debouched to the Pacific or Indian ocean. By 1911 the connection with the Brahmaputra river had become widely accepted but another mystery remained: the river dropped from to in a distance of perhaps which is extremely steep for a river of this size. It seemed there must be a massive waterfall and, indeed, Kinthup had reported one high. In 1913 Frederick Bailey, an intelligence officer with the Indian Army, invited Morshead to be the surveyor in an expedition to explore the Yarlung Tsangpo Grand Canyon (Tsangpo Gorge), now known to be the world's deepest gorge. Bailey and Morshead explored from the south with Morshead surveying the entire route and calculating the results as they went so as not to delay progress. By ascending the Dibang River they crossed the Himalayan watershed into Tibet to reach the Dihang River (Brahmaputra) and ascending the Gorge. When they were at Lagung, just east of Namcha Barwa, they were arrested by the Nyerpa of Pome who took them to Showa on the Po Tsangpo river. After they had been imprisoned for several days they were released. They eventually reached the Dihang river again, this time upstream of the Gorge and just south of Gyala Peri from where they penetrated the massive sweep of the Tsangpo Gorge but only reached Pemakoi-chen where they found the gorge impassible about upstream of Lagung. They returned to India by turning back and passing through eastern Bhutan. The expedition covered on foot and lasted from 16 May to 14 November 1913. In doing this they proved that the Dibang tributary of the Brahmaputra flows around rather than through the Himalayan mountains and does not connect with the Tsangpo. They also proved conclusively that the Tsangpo–Dihang–Brahmaputra was a single river and for the first time established its accurate course. The highest waterfall they found was and they considered there was unlikely to be a higher fall. For his work Morshead was awarded the Macgregor Medal by the United Service Institution of India. At the time the expedition was regarded as a great feat of exploration and it drew international acclaim. War service and return to