In the 19th century, British railway builders had surveyed the Pangsau Pass, which is 1,136 metres (3,727 feet) high on the India-Burma border, on the Patkai crest, above Nampong, Arunachal Pradesh (then part of Assam). They concluded that a track could be pushed through to Burma and down the Hukawng Valley. Although the proposal was dropped, the British prospected the Patkai Range for a road from Assam into northern Burma. British engineers had surveyed the route for a road for the first 130 kilometres (80 miles). After the British had been pushed back out of most of Burma by the Japanese, building this road became a priority for the United States. After Rangoon was captured by the Japanese and before the Ledo Road was finished, the majority of supplies to the Chinese were delivered via airlift over the eastern end of the Himalayan Mountains known as the Hump.
On 1 December 1942, British General Sir Archibald Wavell, the supreme commander of the Far Eastern Theatre, agreed with American General Stilwell to make the Ledo Road an American NCAC operation. The Ledo Road was intended to be the primary supply route to China and was built under the direction of General Stilwell from the railhead at Ledo (Assam, India) to Mong-Yu road junction where it joined the Burma Road. From there trucks could continue on to Wanting on the Chinese frontier, so that supplies could be delivered to the reception point in Kunming, China. Stilwell's staff estimated that the Ledo Road route would supply 65,000 tons of supplies per month, greatly surpassing tonnage then being airlifted over the Hump to China. General Claire Lee Chennault, the USAAF Fourteenth Air Force commander, thought the projected tonnage levels were overly optimistic and doubted that such an extended network of trails through difficult jungle could ever match the amount of supplies that could be delivered with modern cargo transport aircraft.
The road was built by 15,000 American soldiers (60 percent of whom were African-Americans) and 35,000 local workers at a cost of US$150 million. 1,100 Americans died during the construction, as well as many more locals. As most of Burma was in Japanese hands it was not possible to acquire information as to the topography, soils, and river behaviour before construction started. This information had to be acquired as the road was constructed.