Operation Matterhorn was a military operation of the United States Army Air Forces (USAAF) in World War II for strategic bombing of Japan by Boeing B-29 Superfortress bombers based in India, Ceylon, and China. Targets included industrial facilities in Japan and in Japanese-controlled China and Southeast Asia. The B-29s were based in India but staged through bases around Chengdu in China's Sichuan province. Since the Japanese had cut the Burma Road in 1942, the only line of communications with China was over "the Hump", as the air ferry route to China over the Himalayas was called. All the fuel, ammunition and supplies used by American forces in China had to be flown in.
To control the B-29s, the Joint Chiefs of Staff created the Twentieth Air Force under the command of General Henry H. Arnold, the chief of the USAAF, in Washington, DC. The role of the China Burma India Theater (CBI) commander, Lieutenant General Joseph W. Stilwell, was restricted to the provision of logistical support and the defense of the bases. The B-29 force in the CBI was the XX Bomber Command, under the command of Brigadier General Kenneth B. Wolfe. The B-29s required airbases with runways that were longer and stronger than those of smaller bombers. Five airfields in Bengal in India were upgraded to take them. Supplying fuel by rail would have placed too much strain on the railways, so a fuel pipeline to the airfields was laid from the port of Calcutta. The four B-29 airbases around Chengdu, along with five airstrips for fighters to defend them, were built by tens of thousands of Chinese laborers with hand tools.
The XX Bomber Command deployed to India between February and May 1944. On 5 June, Wolfe launched the first B-29 Superfortress combat mission, against the Japanese railroad facilities at Bangkok. Ten days later, 68 Superfortresses took off from the bases around Chengdu to bomb Imperial Iron and Steel Works in Yawata on Kyushu. The Bombing of Yawata was the first air raid on the Japanese home islands since the Doolittle Raid of April 1942, and it marked the beginning of the strategic bombardment campaign against Japan. Other targets included Singapore and the oil refineries around Palembang in the Netherlands East Indies. In October 1944, the XX Bomber Command carried out raids on Formosa in support of General Douglas MacArthur's upcoming return to the Philippines. Later that year, the Japanese offensive Operation Ichi-Go in China threatened the bases. To slow the advance, the XX Bomber Command attacked the Japanese-held city of Hankou with incendiary bombs. The attack left Hankou burning for three days, demonstrating the effectiveness of incendiaries against the predominantly wooden housing stock of the Far East.
In November 1944, American bombers began raiding Japan from the Mariana Islands. The XX Bomber Command abandoned the logistically difficult and increasingly vulnerable bases in China in January 1945, and concentrated its resources on rail and port facilities in Indochina, Thailand, and Burma. This signaled the end of Matterhorn. The 58th Bombardment Wing, the only operational wing of the XX Bomber Command, left India to join the XXI Bomber Command in the Marianas between February and April 1945.
Approximately 800 tons of bombs were dropped by China-based B-29s on Japanese home island targets between June 1944 and January 1945. This was insufficient to produce the desired results. Post-war analysis confirmed that the B-29s would have been better employed in attacks on Japanese shipping or oil facilities in the Southwest Pacific. During Matterhorn, the XX Bomber Command consumed almost 15 percent of the monthly Hump tonnage. Despite those objections, Matterhorn did benefit the Allied war effort by bolstering Chinese morale and demonstrating the B–29's effectiveness against Japanese fighters and anti-aircraft artillery. Subsequent operations from the Marianas profited from the streamlined organization and improved tactics developed during Matterhorn.
Background B-29 Superfortress
On 29 January 1940, the United States Army Air Corps issued a request to five major aircraft manufacturers to submit designs for a four-engine bomber with a range of . These designs were evaluated, and on 6 September orders were placed for two experimental models each from Boeing and Consolidated Aircraft, which became the Boeing B-29 Superfortress and the Consolidated B-32 Dominator. These were known as very long range (VLR) bombers. On 17 May 1941, Boeing was ordered to commence the manufacture of the B-29 when ready.
Boeing devoted its plants in Renton, Washington, and Wichita, Kansas, to B-29 production; assemblies would later also be built by the Bell Aircraft Corporation in Marietta, Georgia, and the Glenn L. Martin Company in Omaha, Nebraska. A major recruiting and training program was required. Many of the workers were recruited from the surrounding areas, and had no experience in aircraft manufacturing. As they became more skilled, the man-hours required to build a B-29 was reduced from 150,000 to 20,000. The $3 billion cost of design and production (equivalent to $ billion today), far exceeded the $1.9 billion cost of the Manhattan Project, and made the B-29 program the most expensive project of the war.
With its wingspan, the B-29 was one of the largest aircraft of World War II. It sported state-of-the-art technology, which included a pressurized cabin, dual-wheel tricycle landing gear, and an analog electromechanical computer-controlled fire-control system that allowed the four gunners to direct five remote machine gun turrets, each with twin Browning .50 caliber machine guns; the rear turret also had a 20-mm cannon. It was powered by four 18-cylinder, Wright R-3350 Duplex-Cyclone radial engines, each with two turbochargers.
The cumulative effect of so many advanced features was more than the usual number of problems and defects associated with a new aircraft. This was compounded by efforts to fast track its introduction into service. These included engine malfunctions, jammed gears and dead power plants. The engines in particular had a large number of defects. The front and rear rows of the engine cylinders were located too close together for efficient cooling; there was insufficient lubrication of the upper cylinders; the reduction drive was prone to failure; and the carburetor produced an inefficient fuel mixture distribution. All of these factors contributed to engine overheating, which resulted in fires owing to an extensive use of magnesium in the crankshaft in order to save weight. In spite of 2,000 engineering changes, the engines remained susceptible to overheating.
Strategy Ostensibly, the B-29 was intended to defend the Western Hemisphere against encroachment by a hostile foreign power, but as early as September 1939, Colonel Carl Spaatz had suggested that it might be used to bomb Japan from bases in Siberia, Luzon or the Aleutian Islands. The Air Corps' first war plan, AWPD-1, issued in September 1941, called for B-29s to bomb Germany from bases in Great Britain and Egypt by 1944. Early war plans did not contemplate bombing Japan until after the war against Germany was won. This continued to be the case after the Japanese attack on Pearl Harbor brought the Allies into war with Japan in December 1941. The idea of basing the Superfortresses in China first surfaced at the Casablanca Conference in January 1943. In March, the Assistant Chief of the Air Staff, Major General Laurence S. Kuter, initiated a detailed study of the possibility of using bombers based in China. No other bases within range of Japan were expected to be in Allied hands in 1944.
Support for China was considered vital by American strategists, as a Chinese collapse would release a quarter of the Japanese Army's divisions for employment elsewhere. Logistic support for the war effort in China was through the port of Calcutta, which was estimated to be able to handle the additional per month required by a bombing campaign. After the Japanese had cut the Burma Road in March 1942, the only line of communications with China was over "the Hump", as the air ferry route to China over the Himalayas was called. Until the Burma Road could be reopened by the ground forces, all the fuel, ammunition and supplies used by American forces in China had flown over the Hump.
The air planners estimated that the first raids on Japan could be mounted as early as April 1944. Their plan called for supplies for bombers based in China to be carried by Consolidated B-24 Liberator bombers converted to Consolidated C-87 Liberator Express transport aircraft. It was estimated that 200 C-87s would be required to support each B-29 bomber group, with 2,000 C-87s in operation by October 1944 and 4,000 by May 1945. Five missions per group per month could be flown, and 168 group-months was believed to be sufficient to destroy all targets in Japan within twelve months.
The staff of the China-Burma-India Theater (CBI) were invited to comment, and they opined that the plan was too sanguine regarding the logistical challenges involved. On request, the CBI Theater commander, Lieutenant General Joseph W. Stilwell, submitted an alternative plan drafted by his air commander, Major General George E. Stratemeyer, codenamed "Twilight", that called for more time, a smaller effort, and reduced logistical support. Under this plan, the bombers would be based in the Calcutta area and only staged through Chinese bases for missions. Keeping the ground crews in India would reduce the logistical footprint in China. Stilwell cautioned that the likely Japanese response to any success by the bombers would be a ground offensive to capture the airfields.
In April 1943, General Henry H. Arnold, the chief of the United States Army Air Forces (USAAF), set up a special B-29 project under Brigadier General Kenneth B. Wolfe. Wolfe became responsible for preparing, organizing and training B-29 units for combat. By September, he had prepared a plan for operations based on Twilight called "Matterhorn"; soon after the Twilight plan was renamed "Drake". The difference between Matterhorn and Drake was that under Matterhorn the B-29s would stage through Chengdu in Sichuan province in western China, whereas under Drake they would stage through Guilin in eastern China. Moving the B-29 bases to western China meant they would be further back from the front lines. This allowed the ground defense to be dispensed with, and the air defenses to be scaled back to two fighter groups that would be assigned to Major General Claire Chennault's China-based Fourteenth Air Force. The plan called for supplies to be stockpiled in China by the B-29s themselves, assisted by the B-24s of Fourteenth Air Force's 308th Bombardment Group. Arnold approved the Matterhorn plan on 12 October.
On 10 November 1943, the president of the United States, Franklin D. Roosevelt, sent a message to the Prime Minister of the United Kingdom, Winston Churchill, asking him to render assistance with the construction of bases in India and one to Generalissimo Chiang Kai-shek asking him to provide labor and materials for the construction of five advanced bases in China, which the United States would pay for under Reverse Lend-Lease. Although Drake still had its advocates, Matterhorn was formally approved by Roosevelt and Churchill at the Second Cairo Conference on 7 December.