The Hump: Flying Over The Himalayan Mountains

The “Hump” refers to the mountainous area at the eastern edge of the Himalayas, north of Myanmar. This was a notorious flight route during the Second World War used by the Allies to fly supplies into the West of China. It was vital in the war effort but is one of the most dangerous routes ever flown, with heavy losses during the three-year operation.

Curtiss C-46
The Curtiss C-46 was the aircraft most used to fly over the Himalaya “Hump.” Photo: USAF via Wikimedia

Flying the Hump between India and China

As part of the Burma campaign during the Second World War, the Allies needed to keep supplies flowing into China. After the Japanese occupation of Burma, the only land routes that could supply Chiang Kai-shek’s forces and civilians in Western China were cut off. To keep China in the war, an alternative supply route was needed.

The solution was a flight route from India, over the mountains, into Western China. Specifically, this was between Assam in India and Kunming in China.  Originally known as the “India China ferry,” it soon became referred to by the pilots that flew it as”The Hump.” Flights began in April 1942, after the Japanese blocked access through Burma, and continued until November 1945.

The Hump route
The Hump route flew over mountainous regions of Southwest China and Burma. Image: The Department of History, United States Military Academy via Wikimedia

Difficult flying conditions

Its nickname explains well the challenges of flying the route. The Himalaya mountains rise high in that region, with the steep mountains and deep ridge causing violent weather conditions and turbulence. Winds were strong (almost jet-stream levels) and very changeable, and temperatures could plummet quickly.

Aircraft also could not fly at the high altitudes they do today. For parts of the route, pilots would have to follow gorges, with mountain ranges higher than the aircraft.

It was not just the winds and terrain that made the route so difficult. The area was relatively unknown, and there was a lack of map and chart details – and certainly not the navigational aids aircraft use today. It was also hard to forecast in advance what conditions would be like, with aircraft often running into bad weather en route. To make it worse, many pilots were new and inexperienced – a common situation with the rapid increase needed during the war. Add to that the fact that the Japanese air force had a presence in the region, and many aircraft were shot down.

Lots of activity, but high losses

Despite the difficulties, the route was vital in taking supplies to the Chinese and resisting the Japanese advance. According to data from the US army, a total of  685,304 tons of cargo was flown eastwards over the Hump – over half of this was supplies of gasoline and oil.

The C-46 was the most numerous aircraft involved in the cargo missions. Many other aircraft, including the C-47 and C-54 were also flown. At the peak of the campaign in 1945, as many as 640 aircraft were involved. In total, 373 aircraft were lost.

Curtiss C-46
A Curtiss C-46, preserved with the USAF Southern California Wing. Photo: Howcheng via Wikimedia

Flying the Hump today

With modern aircraft, flying Himalayan routes is less of a problem. There is still an increased risk of turbulence, but at high cruising altitude, this has minimal impact.

Aircraft do avoid the area north of this, though – the high mountains of the Tibetan plateau. This is partly to do with the chance of turbulence but more to do with the continuous high terrain. With an average elevation of over 14,000 feet, aircraft would not be able to descend to a safe 10,000 feet altitude in the event of an emergency such as cabin depressurization. There are also few diversion airports, necessitating a long flight with limited emergency oxygen.

Take a look at this image from showing the typical distribution of aircraft in the region. You will note the whole Tibetan plateau region is empty of flights, with aircraft tracking to the north and south.

RadarBox Tibet
Flights to and from Asia avoiding the Tibetan plateau. Flight data:

There is plenty more to discuss about the Hump operations, routes, and aircraft than we can cover in this summary. Feel free to bring up more in the comments.