'Notebook' was the US air transport build-up to deliver supplies and equipment from India to China over the 'Hump' of the eastern Himalayan mountains (autumn 1943).

US air crews started to make deliveries 'over the Hump' during April 1942 after Japanese land forces had cut the Burma Road, and continued to do so until 1945 when the opening of the Ledo Road.

Flying 'over the Hump' was a singularly dangerous undertaking as the air route led first over the Himalayan foothills and finally to the mountains, between northern Burma and western China, where violent turbulence and terrible weather was standard. Transport aircraft flew around the clock from any of 13 bases in north-eastern India, landing about 500 miles (805 km) away at one of six Chinese airfields. Some crews flew as many as three round trips every day. As a result of the region’s isolation, parts and supplies to keep the aircraft serviceable were always in short supply, and flight crews were often sent into the foothills to gather up the debris from previous crashes for parts to repair their squadrons' remaining aircraft. The area overflown by the 'Hump' route is cut by the great parallel gorges of the upper parts of some of the largest waterways of South-East Asia, such as the Mekong, Irrawaddy and Salween rivers.

Aviation equipment was ferried to China across the Himalayan 'Hump' from a time in May 1942, and reflected the need to maintain an uninterrupted supply to China of strategic materials requested by the Nationalist government of Generalissimo Chiang Kai-shek. The air bridge was 'built' by transport aviation units of the US Army and the air transport section of the Chinese Air Company which, in the period between 1942 and 1945, received from the USA exactly 100 transport aircraft in the form of 77 Douglas C-47 Skytrain and 23 Curtiss C-46 Commando machines.

Thus between India and China there developed an airlift of major size and importance.

In the west the 'Hump' route began in India and passed over the mountains of Yongnan and a series of spines to Sichuan province in south-western China. After the opening of the air route, the amount of freight rose steadily: the quantity transported reached 7,000 tons every month. According to the reckoning of the Chinese, from May 1942 to September 1945 some 650,000 tons were transported, of which Chinese pilots accomplished 75,000 tons. The air bridge also carried 33,400 people. In spite of poor weather conditions, with inadequate navigational resources (there were not enough navigators for all the groups) the US and Chinese pilots transported cargo to Chengdu, Kunming and other cities on a daily basis. The operation was accompanied by major losses from adverse weather, equipment failures, and Japanese fighter attack. It all, 468 US and 46 Chinese crews (more than 1,500 men) were lost.