(Inside Science) -- In April 1942, a few short months after the Japanese attack on Pearl Harbor, the U.S. military began a mission that tested the technical capabilities of its aircraft and the courage of its personnel. The mission, designed to supply otherwise isolated Chinese forces and civilians after the Japanese cut off the only land-based supply route through Burma, was called "Flying the Hump."
Sometimes scientific and technological advances can win a war. See the atomic bomb. But the Hump airlift owed its success primarily to courage and imagination.
The Himalaya mountains, the tallest in the world, ran through what was formally called the China-Burma-India Theater (CBI). The men who crossed them used aircraft not designed to fly that high, carrying loads heavier than they were designed to carry, in weather no one was supposed to fly through.
By the end of the war, the airlift was moving 77,306 tons of supplies a month, operating 622 aircraft supported by 34,000 U.S. military personnel and 47,000 civilians. When the books were closed after the war, the army reported 509 plane crashes, 1,314 crew members known dead, and more than 300 missing.
Early on, the airlift was the work of C-47s -- converted DC-3 twin engine airliners, also called Dakotas by the British and Gooney Birds by their crews. The floor of the standard airliner's main body had been reinforced, the tail shortened to pull gliders, and a cargo door added. It could carry up to 24 men, or an assembled jeep, or 14 stretcher patients and three nurses.
Lacking cabin pressurization, the planes should have been limited to 10,000 feet. But for 140 miles of the route, the mountains were never lower than 12,000 feet. Everyone on board usually had to wear uncomfortable oxygen masks.
The C-47s were eventually replaced by C-46s, which were supercharged, four engine planes that could fly higher, faster, and with more cargo. The C-46s had a unique wing design, the Davis wing, that was thicker and provided more lift. But the planes were difficult to fly at high altitudes, and they iced over readily. More than a few fell from the sky like stones. Crews hated them because they crashed more frequently than other planes and were exceptionally uncomfortable to crew; commanders liked the capacity.
They also were unpressurized.
After a few months, all the planes broke down, said Herb Seubert, of Jacksonville, Florida, now 99. He flew 30 roundtrip missions over the Hump.
Eventually, the C-46s were replaced by the Douglas C-54, a variant of the DC-4 airliner, which became the standard long-range aircraft. They could carry 10 times the cargo of the C-47. They could fly 4,000 miles and had a ceiling of 22,000 feet, but were still unpressurized, limiting how high they could fly with passengers. One specialized C-54 variation became President Franklin Roosevelt’s personal plane, dubbed the Sacred Cow.
Using aircraft that were better-suited to the mission didn't make it easy.
"In late 1944, the operation was flying mostly daylight and good weather," wrote radio operator Wendall A. Phillips. To increase tonnage, the planes were ordered into the air in any weather and 24 hours a day. "Of course, the tonnage rapidly improved but, so did our losses in 'Aluminum Alley,' as we called it," he said. "The Hump became littered with our aircraft. On a clear day, you could see the sun reflecting off the wreckage of crashed planes lying there."
The supply flights brought everything from troops and basic supplies, to a cow needed to supply milk to a remote base, light weapons, and even a falcon to attack Japanese carrier pigeons (with mice aboard to feed it). The main cargo was aviation fuel in 55-gallon drums.
It was always a battle between aircraft and weather conditions. While turbulence around mountains (the "mountain effect") is common, planes flying the Hump sometimes hit winds of hurricane velocity, a buffeting they were not built to withstand. Crew members could only hang on and hope the wings didn’t break off. Some apparently did. The winds were particularly vicious during the monsoons, July through September.
"You could drop a couple of thousand feet very quickly," Seubert said.
"Above the Hump, cumulo-nimbus clouds mass together to heights beyond the ceiling of the Dakotas [C-47s]," wrote Royal Air Force Commander Henry Probert. "In certain forms these clouds are impenetrable, and out of such types of cloud no aircraft has been known to emerge unbroken."
Stuart Arnold, now 95 and living in Brisbane, Australia, said the route was so dangerous the RAF would only send volunteers. He volunteered.
Communications were poor, aeronautical maps were unreliable and weather reporting almost nonexistent. P-40 fighters, which escorted the cargo planes, came with no radio at all, so the crew members installed transmitters built for Piper Cubs. Homing beacons were positioned at every refueling airport, but the weather often blocked them out. Pilots would sometimes use a commercial radio station just over the line in China as a guide.
Maintenance was always an issue, with insufficient spare parts and a shortage of mechanics. Heat and humidity made living conditions difficult. The planes were famously uncomfortable, with the gunner or passengers in the C-46 having to sit on the floor in a plane with no heater.
Seubert, an operations officer, said that if a plane failed to return to base, the command would send out another plane to try to communicate with the missing aircraft. If the second crew succeeded in getting contact, it would drop supplies and initiate a rescue that could include parachuting a flight surgeon to the scene. The rescue team would carry trinkets to bribe the local people, who had a reputation as headhunters.
Some less urgent issues, like lack of refrigeration at the bases, were resolved with ingenuity.
"During hot days, the men would fill a canteen or other shatter-proof vessel with water, stick it in a hole in the side of a military aircraft, and have the pilot fly to high altitude," one veteran, Alfred Timpani, told his family. "Retrieving the container when the plane landed provided a welcome cold drink."
Some things couldn’t be fixed. An especially fast agile fighter, the P-38, had a unique design: engines and propellers on two connected booms with the pilot sitting in a pod in between. Unfortunately, at low altitude in the tropics, the pod got so hot that some pilots flew the plane in combat wearing just their underwear. Nonetheless, the P-38 Lightning was the plane used by America’s top fighter aces.
With the danger and the hardships, morale was low, Seubert said. CBI became known as "Constant Bickering Inside" because the high command had problems agreeing.
Another land route, the Ledo Road, was built in early 1945. The airlift continued to play a crucial role until the war ended that August.
A touring exhibit about WWII collaborations between the U.S. and China has recently been displayed in multiple locations, including the Pentagon and a museum in Pearl Harbor.
Veterans like Seubert used to stay in touch through the Hump Pilots Association, but the group disbanded in 2005 when membership became negligible.
Now, more than 70 years after the war ended, Seubert has lost track of his fellow Hump veterans.
"They are all dead," he said.
Many of the Hump veterans felt their efforts were unappreciated and called their experience the "lost campaign."
"I would not presume to believe that I had conquered the Hump,” Arnold wrote in his diary. "I gave it my best shot, and after 58 crossings, bade it farewell, grateful that I had not encountered it in full fury."
Editor's note: The story has been edited to reflect that the C-46 cargo plane was not a converted B-24 Liberator. We regret the error.