Operation Matterhorn
Part of the China Burma India Theater of World War II
B-29 bomber bases in China and the main targets they attacked in East Asia during Operation Matterhorn
Location	East Asia and Southeast Asia
Commanded by	Kenneth Wolfe LaVerne Saunders Curtis LeMay
Date	1944–1945
Executed by	XX Bomber Command

Operation Matterhorn was a military operation of the United States Army Air Forces in World War II for strategic bombing by Boeing B-29 Superfortress bombers based in India, Ceylon and China. Targets included industrial facilities in Japan, China and Southeast Asia.

The B-29 was one of the largest aircraft of World War II and had state-of-the-art technology. The cumulative effect of 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. The concept of basing them in China arose because no other sites within range of Japan were expected to be in Allied hands in 1944. 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 American forces in China had flown in.

To control the B29s, the Joint Chiefs of Staff created the Twentieth Air Force under the command of General Henry H. Arnold, the chief of the United States Army Air Forces (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-29s force in 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, sixty-eight Superfortresses took off from the bases around Chengdu to bomb Imperial Iron and Steel Works in Yawata on Kyūshū. 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 late 1944, 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, proving 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. in India. 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 in March 1945.

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 2,000 miles (3,200 km). 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.^[1] These were known as very long range (VLR) bombers.^[a] On 17 May 1941, Boeing was ordered to commence the manufacture of the B-29 when ready.^[1]

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.^[1] 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.^[3] The $3 billion cost of design and production (equivalent to $49 billion today), far exceeded the $1.9 billion cost of the Manhattan Project, made the B-29 program the most expensive of the war.^[4][5][6]

With its 141-foot (43 m) wingspan, the B-29 was one of the largest aircraft of World War II.^[7] 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.^[8][9] It was powered by four 18-cylinder, 2,200-horsepower (1,600 kW) Wright R-3350 Duplex-Cyclone radial engines, each with two turbochargers.^[8]

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.^[8] 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;^[10] 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 sometimes resulted in fires owing to an extensive use of magnesium.^[11] In spite of 2,000 engineering changes, the engines remained susceptible to overheating.^[6]

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.^[12] The idea of basing the Superfortresses in China first surfaced at the Casablanca Conference in January 1943.^[13] In March, the Assistant Chief of the Air Staff, Major General Laurence S. Kuter, initiated a detailed study of the possibility of using VLR bombers based in China. No other bases within range of Japan were expected to be in Allied hands in 1944.^[14][15]

Support for the effort was through the port of Calcutta, which was estimated to be able to handle the additional 596,000 short tons (541,000 t) per month. From there, supplies would be flown to China in Consolidated B-24 Liberator bombers converted to Consolidated C-87 Liberator Express transport aircraft.^[14] 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 American forces in China had flown over the Hump.^[16] It was estimated that 200 C-87 flights would be required to support each VLR 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, with 168 group-months believed to be sufficient to destroy all targets in Japan within twelve months.^[14][15]

The staff of the China-Burma-India Theater (CBI) were invited to comment, and they opined that the plan was too optimistic about 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.^[14][17] It was estimated that the first raids on Japan could be mounted as early as April 1944.^[18]

In April 1943, the commander of the United States Army Air Forces (USAAF), General Henry H. Arnold, 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".^[19] 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 further back from the front lines allowed the ground defense to be dispensed with, and the air defenses scaled back to two fighter groups that would be assigned to Major General Claire Chennault's China-based Fourteenth Air Force. Supplies would 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 plan on 12 October.^[19]

On 10 November 1943, President Franklin D. Roosevelt sent a massage to Prime Minister 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.^[20][21] Although Drake still had its advocates, Matterhorn was formally approved by Roosevelt and Churchill at the Sextant Conference in Cairo on 7 December.^[22][23]

The British and American Combined Chiefs of Staff had authorized a Central Pacific drive that included the capture of the Gilbert and Marshall Islands, Truk, Palau and the Mariana Islands.^[24] but it was not considered likely that they would be available before 1945.^[25] The air staff planners began incorporating the Marianas into their plans as a potential base for the B-29s in September 1943.^[14] This was formally approved at Sextant.^[26] By January 1944, there was consideration of advancing the Central Pacific timetable by bypassing Truk and heading directly for Palau after the capture of the Marshalls, but senior army and navy officers in the Pacific doubted the utility of basing B-29s in the Marianas due to the limited harbor facilities there.^[27]

A study by the Joint War Plans Committee (JWPC) assessed the Mariana Islands as the best location for the deployment of the B-29s, but in view of the fact that they would not be captured until later in the year, recommended that the first B-29 groups be deployed to the Southwest Pacific Area to attack the petroleum refineries in the Netherlands East Indies or to India and China to attack industrial targets in Japan.^[28] The timetable for the Central Pacific advance was revised in March 1944: Truk was to be bypassed and the Palau operation was postponed until 15 September, after the capture of the southern Mariana Islands, which was now scheduled to commence on 15 June 1944. The new timetable was approved by the Joint Chiefs of Staff on 12 March.^[29][30]

Target selection

In March 1943, Arnold had asked the Committee of Operations Analysts (COA) to prepare an analysis of strategic targets in Japan whose destruction might affect the course of the war. Moat of Japan's war industries lay within the 1,500-mile (2,400 km) range of a B-29 with a ten-ton bomb load. The COA had been created in December 1942, and its membership included officers from the Army and Navy, along with distinguished civilians consultants such as Edward M. Earle, Thomas W. Lamont, Clark H. Minor and Elihu Root Jr. In a report delivered on 11 November 1943, they identified six priority economic targets: merchant shipping, steel production, urban industrial areas, aircraft plants, ball bearings, and electronics.^[31]

Particular vulnerable were the ball bearing industry, which relied on six major plants, and the steel industry, which was dependent on a small number of coke plants located on Kyushu and in Manchuria and Korea—all within range of B-29s based at Chengdu.^[31] The analysts assessed the capacity of the Japanese steel industry at 13,690,000 short tons (12,420,000 t) per year, which was very close to the real figure, but erroneously thought that it was running at full capacity. In fact, the bombers would have to destroy 5,000,000 short tons (4,500,000 t) of capacity to have any impact on production.^[32]

The JWPC also considered targeting, but favored shipping and the oil industry, which could more easily be attacked from bases in Australia. The staff of the USAAF accepted the importance of targeting shipping, but it was not what the B-29 was designed for. As for the oil industry, the oil refineries in the Dutch East Indies, primarily the ones at Palembang, could be attacked by B-29s based in India, staging through Ceylon.^[33] The Joint Chiefs of Staff approved the Matterhorn plan on 10 April 1944, but cut the force to just one wing of four groups. In recognition of the accelerated schedule for the capture of the Marianas, the second B-29 wing would be sent there instead, or to Australia if bases in the Marianas were not yet ready.^[33][28]

Command and organization

To control the B-29s, the 58th Bombardment Wing was activated at Marietta Army Air Field, near Bell's B-29 plant, on 1 June 1943, and Wolfe had assumed command on 21 June.^[34] Although he had an experience in engineering and development in the United States and the Philippines, and an excellent knowledge of the B-29, he had no upper echelon command or operational experience. He did however have a free hand in selecting officers for his organization. Many came from his former command at Wright Field, Ohio, including the leading expert on the B-29, Colonel Leonard F. Harman, who became his deputy. For his assistant chief of staff for operations (A-3), he secured Brigadier General LaVerne G. Saunders, who had been awarded the Navy Cross while in command of the 11th Bombardment Group during the Guadalcanal campaign.^[34][35]

The Second Air Force provided four airfields for training in the vicinity of Salina, Kansas, not far from Boeing's Wichita plant where most of the early model B-29s were made, and the 58th Bombardment Wing moved its headquarters to Smoky Hill Army Air Field near Salina on 15 September. The wing was initially under the direct control of USAAF headquarters, but on 11 October it was assigned to Second Air Force. The XX Bomber Command was activated in Salina, on 27 November 1943, with Wolfe as its commander, and Harman became the commander of the 58th Bombardment Wing.^[34]

The group commanders had a wealth of experience. The 444th Bombardment Group was led by Colonel Alva L. Harvey, who had been a test pilot for the Boeing B-17 Flying Fortress bombers and had participated in the first American bombing raid on Berlin.^[36][37] Colonel Richard H. Carmichael led the 462nd Bombardment Group; he had formerly commanded the 19th Bombardment Group in the Southwest Pacific Area, and had led the first B-17 raid on Rabaul in February 1943.^[36][38] Colonel Howard E. Engler commanded the 468th Bombardment Group until August 1944, when he was replaced by Colonel Ted S. Faulkner.^[39] The 40th Bombardment Group was commanded by Colonel Lewis R. Parker. He was sent to England to obtain combat experience with the Eighth Air Force and was shot down on his second mission over Germany on 6 March 1944. He was replaced by Harman in April 1944, and Saunders succeeded him as commander of the 58th Bombardment Wing.^[36][40]

Brigadier General Haywood S. Hansell Jr., the Deputy Chief of the Air Staff and the Acting Assistant Chief of the Air Staff for Plans, was appointed the chief of staff of the Twentieth Air Force.^[41] As the air member of the JWPC, he was familiar with plans for the deployment and use of the B-29.^[33] He held his first staff meeting on 12 April. He was the de facto commander of the Twentieth Air Force,^[41] especially after Arnold suffered a heart attack on 10 May 1944.^[42][43]

The table of organization and equipment for the B-29 groups was authorized on 13 January 1944. Each aircraft had a crew of eleven. Five were officers: the pilot-commander, co-pilot, two navigator-bombardiers, and the flight engineer. The other six were enlisted personnel: an engine mechanic, electrical specialist, power-plant specialist, central fire-control specialist, radio operator, and radar operator. Each squadron had seven aircraft, and each of the four groups had four squadrons, so the wing had 112 B-29s. Each B-29 had two crews, so the wing had 3,045 officers, 8 warrant officers and 8,099 enlisted men. With the service and maintenance units and aviation engineers to build the airfields, Wolfe would have about 20,000 men under its command.^[44]

Wolfe and an advanced echelon of his XX Bomber Command staff arrived in New Delhi on 13 January 1944, where he met with Stratemeyer. On 3 February he met with Stilwell at the latter's advanced headquarters in Burma to discuss command arrangements. They agreed that the XX Bomber Command should not come under Chennault's command, nor under that of Stratemeyer, who was answerable Admiral Lord Louis Mountbatten, the commander of South East Asia Command (SEAC). Stilwell feared that Chennault would use the B-29s to attack Japanese shipping and thereby provoke a strong Japanese reaction that would be beyond the ability of the Chinese army to oppose. He therefore issued a directive on 15 February that placed the XX Bomber Command under his own direct command and control.^[48][49]

Command and control of the B-29s was subject to further debate among the Joint Chiefs of Staff. To avoid the B-29s being misused on the battlefields when they would be much more useful against the Japanese home islands, the Commander in Chief, United States Fleet, Admiral Ernest J. King, suggested that an air force be created under Arnold's command. Arnold would be responsible for its administration and logistical support, and would control it as the executive agent of the Joint Chiefs of Staff, who would determine its deployment and missions. The Joint Chiefs approved the establishment of the Twentieth Air Force on 4 April 1944. This gave the USAAF equal status with the ground and naval forces in Asia and the Pacific for the first time. Stilwell's role as commander of CBI would be restricted to providing logistical support and the defense of the B-29's bases.^[50][28]

Training and preparation

As well as the recruitment of senior staff, Wolfe was authorized to procure twenty-five pilots and twenty-five navigators with experience of long over-water flights in four-engine aircraft. The training of the crews of the 58th Bombardment Wing was rendered difficult by the shortage of B-29s. The first prototype XB-29 was turned over to the USAAF shortly after the 58th Bombardment Wing was formed in June 1943, but the first production B-29 did not arrive until August. In the meantime, crews trained on fifty Martin B-26 Marauders. These were subsequently replaced by B-17s, which were more like the B-29. By November 1943 there was still only one B-29 between twelve crews. A month later they had flown an average of just 18½ hours in the B-29, and only 67 commander-pilots were fully qualified on the B-29. In view of this, the number of crews to be trained was reduced to 240, and the date of completion of their training was postponed from 1 February to 1 March.^[51]

By February 1944, the entire XX Bomber Command had only flown 9,000 hours in B-29s, and few of these were above 20,000 feet (6,100 m) due to issues with the power plant. Ninety-seven B-29s had been delivered, but two of them had the central fire control system installed, and it had not been fully tested.^[52] The late delivery of the aircraft seriously dislocated the crew training program, and many of the crews lacked sufficient training in high-altitude formation flying, gunnery, and visual and radar bombing.^[53]

Arnold had hoped that the B-29s would be ready by January 1944, but on 12 October 1943 he notified Roosevelt:

In connection with the bombing of Japan from China by B-29s, I regret exceedingly to have to inform you that there has been a holdup in production of engines. It looks now as if it will be impossible to get the required number of B-29s together in China to start bombing before the first of March, and with the possibility of not getting them there before the first of April. At this writing I expect to have 150 B-29s in China by March 1st, of which 100 can be used against Japan.^[54]

He visited the B-29 plant in Wichita on 11 January 1944 and had his name written on the 175th aircraft, and told the workers that he wanted it delivered by 1 March 1944.^[55][56] The aircraft, Superfortress 42-6365 General H. H. Arnold Special, was delivered on 24 February 1944.^[57][58] Changes disrupted the delivery of key parts. Because so many modifications had been made while aircraft were being built, it had become standard practice to fly new B-29s direct from the factory to a modification center to be upgraded. The modification centers were overworked, and had limited hangar space, so much of their work had to be done in the open air. When Arnold visited Pratt Army Air Field on 8 March 1944, he found no B-29s ready for combat. ^[55][56]

Arnold designated Brigadier General Bennett E. Meyers, who was traveling with him, as special project cocoordinator, with responsibility for getting the B-29s ready. Meyers chose Colonel Clarence S. Irvine as his deputy. Boeing provided 600 workers, although this slowed work on the production lines. The deficiencies of each aircraft were cataloged and spare parts were obtained. Work was carried out in appalling Kansas winter conditions, with snowstorms and outdoor temperatures between −2 and 20 °F (−19 and −7 °C). By 15 April, 150 aircraft were combat ready.^[55][56]

Base development

India

Airbases

A team headed by Brigadier General Robert C. Oliver, the commander of the CBI Air Service Command, began inspecting potential sites for B-29 bases in August 1943. The B-29's 141-foot (43 m) wing span was considerably wider than the 104-foot (32 m) of the B-17, the next largest aircraft in the inventory, and a fully-laden B-29 weighed about 70 short tons (64 t), nearly twice as much as a B-17. The Twentieth Air Force asked for B-29 runways to be 8,500 feet (2,600 m) long and 200 feet (61 m) wide, nearly twice the area of a 6,000 by 150 feet (1,829 by 46 m) B-17 runway. The plan was to enlarge and improve five existing runways in the flatlands west of Calcutta to bring them up to B-29 standards. Five airfields were selected on 17 November: Bishnupur, Piardoba, Kharagpur, Kalaikunda and Chakulia. Wolfe's advance party from the XX Bomber Command inspected the fields in December and accepted all but Bishnupur, for which Dudhkundi was substituted.^[59][60]

Work was to be carried out by US Army engineer units with imported materials and local labor. Company A of the 653rd Topographic Battalion surveyed the sites to determine how the airfields could be constructed. In order to get the runways operational as soon as possible, the airmen were persuaded to temporarily accept runways 7,500 feet (2,300 m) long and 150 feet (46 m) wide. Lieutenant Colonel Kenneth E. Madsen was in charge of construction of the air bases; Colonel William C. Kinsolving, a petroleum engineer, had the task of laying two four-inch (100 mm) pipelines to the airfields. They reported to Colonel Thomas Farrell, who headed the CBI Construction Service.^[61][60]

Each air base would require four months' work by an engineer aviation battalion. In order to meet the April deadline, the engineer units should have been in place by December, but they were still in the United States. Stillwell gave them priority for shipping, and they set out on a convoy that sailed on 15 December. Travelling via North Africa, they reached India in February 1944 In the meantime, local contractors and 300 trucks were borrowed from the Engineer-in-chief of the British Eastern Command.^[61][60]

The delay in sending the engineer units threatened to upset the entire Matterhorn timetable. On 16 January 1944, Stilwell diverted the 382nd Engineer Construction Battalion from working on the Ledo Road to working on Kharagpur. It deployed by air, taking over equipment on site. The 853rd Engineer Aviation Battalion arrived in the theater on 1 February and was set to work on Chakulia. Units from the 15 December convoy began arriving in mid-February. The 930th Engineer Regiment was assigned to Kalaikunda, the 1875th Engineer Aviation Battalion to Dudhkundi, the 1877th Engineer Aviation Battalion to Chakulia, and the 879th Engineer Aviation Battalion (Airborne) to Piardoba. As an airborne unit, the 879th was equipped with small, air-portable equipment that was unsuited to airbase work, and was eventually reassigned.^[62][63]

The units worked with borrowed equipment; their unit equipment did not begin to arrive until 15 April, and was not complete until 30 June. Marshall accepted a proposal from Stilwell and Mountbatten to divert units earmarked for amphibious operations in Burma to Matterhorn. Accordingly, he assigned the 1888th Engineer Aviation Battalion. It embarked from the West Coast of the United States in February, and reached India in mid-April. With its arrival, Madsen had 6,000 engineers and 27,000 Indian civilians under contract from India's Central Public Works Department on the job.^[62][63] Religious sensibilities meant that seven different types of rations had to be stocked.^[64]

Grading of the runways accounted for more than half of the 1,700,000 cubic yards (1,300,000 m³) of the earth moved. New concrete was laid 10 inches (25 cm) tick; existing runways were overlaid with 7 inches (18 cm) of concrete. While sand was obtained from nearby streams and gravel and crushed basalt construction aggregate were obtained locally, Indian cement was in short supply and of inferior quality, so much of the cement was imported from the United States. Concrete was produced locally and spread by hand at all the fields except Kalaikunda, where heavy equipment was used. Chevron- and horseshoe-shaped hardstands were provided, as were paved, rectangular parking areas. To save time and concrete, dispersal areas were omitted.^[65]

A variety of buildings were provided. At first the troops lived in tents, but later they were housed in native "basha" huts with earth or concrete floors, bamboo or plaster walls and thatched roofs. Basha huts were also used for administrative and technical buildings, along with U.S. prefabricated plywood structures, some of their Italian counterparts that had been captured in the East African campaign, and British Nissen huts. Workshops and hangers were also provided. Most of the utilities such as electricity and water were installed by U.S. Army engineers.^[65]

Although reports to USAAF headquarters frequently claimed that work was proceeding on schedule, that schedule was far behind the original plans, and works on the airbases were not completed until September. The decision in April to deploy the send wing of B-29s to the Marianas meant that only four groups would be deployed to CBI instead of the originally eight, so only the five original airfields were required. Delays in construction at Dudhkundi meant that Charra Airfield had to be used as a temporarily. The B-24 runway there was extended to accommodate the 444th Bombardment Group until Dudhkundi was ready in July. The total cost of constructing the five airbases was estimated at $20 million (equivalent to $332.48 million in 2022).^[65]

Pipelines

Supplying fuel to the airfields in Bengal by rail would have placed too much strain on the railways, so a fuel pipeline to was laid from Calcutta to the airfields.^[66] It was estimated that the Matterhorn bases would require 4,736,000 US gallons (17,930,000 L) of fuel in March 1944, 3,536,000 US gallons (13,390,000 L) in April and May, 7,027,000 US gallons (26,600,000 L) in June, 7,077,000 US gallons (26,790,000 L) in July, and 10,608,000 US gallons (40,160,000 L) in August. Each airbase was provided with 1,470,000 US gallons (5,600,000 L) of storage.^[67]

A Shell Oil terminal at Budge Budge had a tank farm with a capacity of 500,000 barrels (79,000,000 L), of which 300,000 to 400,000 barrels (48,000,000 to 64,000,000 L) were made available to the U.S. Army. The 700th Engineer Petroleum Distribution Company arrived at Kalaikunda on 3 January 1944, and was given the task of laying a six-inch (15 cm) pipeline from Budge Budge to Kharagpur, a distance of about 60 miles (97 km). The 707th and 708th Engineer Petroleum Distribution Companies arrived a few days later and were assigned the task of laying four-inch (10 cm) pipelines from Kharagpur to Chakulia via Dudhkundi, and from Kharagpur to Piardoba respectively. Each four-inch line was about 50 miles (80 km) long.^[68]

A major obstacle was the Hooghly River, which had a tidal bore of up to 7 feet (2.1 m) and a current that could reach 25 miles per hour (40 km/h). Heavy pipeline clamps were attached every few joints to hold the pipe in position on the bottom. Laying 5,000 feet (1,500 m) of pipeline across involved scheduling the work for optimal tidal conditions. The pipe was run across with steel cables pulled by large Caterpillar D8 tractors. Three pump stations were established: one at Budge Budge, one at Kharagpur, and one halfway between them. The system began pumping gasoline on 13 March 1944. The 707th operated the system, while the 700th and 708th moved on to other projects.^[68]

Due to a shortage of standard pipe, Farell and Kinsolving decided to use thin, light-weight, "invasion-weight" pipe.^[64] Pipes were buried to prevent accidental or deliberate damage in densely populated areas.^[65] Local labor was required to dig the ditches. "And the contractors' personnel policies, if they can be so dignified, were blends of inefficiency and time-honored skulduggery."^[69] The invasion-weight pipe was susceptible to corrosion and leaking 100-octane gasoline could be dangerous. On 26 June 1944, a leak was found where the pipe crossed the Hooghly River near the village of Uluberia. Five days later, a vapor explosion set fire to thatched houses in the village. Seventy-one people died in the ensuing conflagration.^[70][71]

China

Lieutenant Colonel Henry A. Byroade was appointed the project engineer responsible for construction of the B-29 airfields in China. He personally reconoitered the Chengdu area in November 1943, and in his report on 8 December he selected four B-29 airbase sites, Xinjin, Guanghan, Qionglai and Pengshan, where existing runways could be strengthened and lengthened to accommodate the B-29s.^[60] In addition, there were five airstrips for fighters.^[72] On 16 March 1944, Byroade assumed the dual role of chief engineer of the 5308th Air Service Area Command and chief engineer of the Fourteenth Air Force.^[73]

At the Sextant Conference in Cairo, Roosevelt promised the Chiang that the United States would fully reimburse China for labor and materials expended on Matterhorn. The Chinese estimated that the airbases would cost two to three billion Chinese yuan, around $100 to $150 million (equivalent to $1,300 to $2,000 million in 2022), at least at the official rate of exchange;^[74] on the black market an American dollar fetched up to 240 Chinese yuan. Stilwell suspected that half of this sum was in the form of "squeeze" (bribes and commissions), an accepted business practice in China.^[75] "One more example", he wrote in his diary, "of the stupid spirit of concession that proves to them that we are suckers."^[75]

A settlement was reached between the Vice Premier of the Republic of China, Kung Hsiang-hsi, and the United States Secretary of the Treasury, Henry Morgenthau Jr., in June, under which the United States paid China $210 million (equivalent to $2,800 million in 2022), although this included payment for other works in addition to the Chengdu airfields.^[76] Arthur N. Young, the American financial advisor the Chinese government was critical of the U.S. Army's profligate spending.^[77] Price caps on materials were imposed used by contractors, but with limited success.^[76] It became necessary to fly banknotes over the Hump.^[78] Landowners were inadequately compensated for the loss of their land and the peasants who worked it were not compensated at all.^[77] Contract workers were paid on a piecework basis, and averaged about 25 Chinese yuan per day. This was barely sufficient to buy food, so many had to be supported by their families.^[76] These grievances generated support for the Chinese Communist Party.^[77]

The work was the overall responsibility of Zhang Qun, the governor of Sichuan Province. Zeng Yangfu, the head of the Ministry of Transportation and Communications, provided engineering, design and planning support.^[72] Construction work was supervised by Lieutenant Colonel Waldo I. Kenerson.^[60] Only fourteen U.S. Army engineers were assigned to the project.^[79] Their role was limited to drafting specifications, carrying out inspections and administering the work. The Chinese Military Engineering Commission controlled construction.^[60] Some 300,000 impressed laborers and 75,000 contract workers were employed on the project.^[66] Kenerson found that he had to teach them about soil mechanics, and then supervise them to ensure what he told them was put into practice.^[73]

Chinese laborers assembled for the project were organized in groups of 40,000 to 100,000 according to their local xian (counties); each xian was responsible for supplying a quota of workers. Workers had to provide their own tools and bring ninety days' rations with them.^[79] Food and accommodation were provided by the Chinese War Area Service Corps.^[66] The Chinese authorities insisted that workers from different xian could not be mixed, so each xian was allocated a portion of the project. The workers established temporary camps near the bases, which minimized travel time and facilitated health care and sanitation. Cooks provided meals of rice and steamed vegetables in baskets. Meat was provided once a week.^[79]

Since communications between China and India were solely by air, it was impractical to bring cement, asphalt or concrete mixers to China from India. The Chinese airfields had to be made entirely from local rock, gravel and sand.^[60] Farrell sent some small rock crushers and provided a detachment of engineers to install the fuel handling systems.^[73] Because the B-29 runways could not be brought up to standard, they were built to the full length of 8,500 feet (2,600 m) to allow for an extra margin of safety.^[74] They were 19 inches (48 cm) deep, with 52 hardstands for each. The accompanying fighter strips were 4,000 feet (1,200 m) long, 150 feet (46 m) wide, and 8 to 12 inches (20 to 30 cm), with 4 to 8 hardstands each.^[80] Strucrtures totaling 19,000 square meters were built, and each base had a oil storage tank.^[81]

Some 1,000 ox carts, 15,000 wheelbarrows and 1,500 trucks were used to carry building materials. There were no bulldozers, power shovels or graders. The topsoil and some of the subsoil was removed, with hoes, and was carried away in wicker baskets on shoulder poles by men and boys. The subsoil was rolled flat using huge concrete rollers hauled by up to 300 workers. A layer of pebbles taken from nearby streams was laid down using wheelbarrows.^[80][82] Over 300,000 cubic meters were used for the runways and taxiways.^[81] Workers collected them from the banks of the Min River. As this source became depleted, they waded into the freezing rapids and shoals to collect them from the riverbed.^[83] Rocks had to be used to supplement the pebbles. Women and girls shaped them with hammers and chisels so they would not shift about. A slurry of topsoil and subsoil was laid atop the rocks as a binder, which was then rolled flat. Successive layers of rock and slurry were laid down.^[80][82]

Saunders landed the first B-29 at Guanghan on 24 April, where he was met by officials including Wolfe, Chenanult and Zhang.^[84] All four airfields were completed by 10 May 1944.^[80][85]

Ceylon

In addition to raids on Japan from bases in China, the Sextant Conference also approved attacks on the oil refineries in the Dutch East Indies by B-29s based in India, staging through Ceylon, with a target date of 20 July 1944. Although the southeast corner of Ceylon would have been the best location from a tactical point of view, being closest to Palembang, it was rejected due to the poor communications with that part of the island.^[86]

Airbase construction in Ceylon was a SEAC responsibility. When Kuter paid Mountbatten a visit in Colombo on 5 March, he found work under way on bomber airstrips at Kankesanturai in the north and Katunayake in the west, with completion dates in late 1944 or early 1945. Neither was well-situated for the proposed B-29 missions. The British then offered to extend airfields at Minneriya and China Bay, and this was accepted. By April it was apparent that the deadline could not be met. Work on Minneriya was suspended and effort concentrated on China Bay. By mid-July there it had a 7,200-foot (2,200 m) runway with hardstands, fuel pumps and accommodation for 56 B-29s.^[86]

Deployment

Sealift and airlift

The Matterhorn plan called for 20,000 troops and 200,000 short tons (180,000 t) of cargo to be shipped from the United States to CBI between 1 January and 30 June 1944, followed by 20,000 short tons (18,000 t) of fuel per month starting in April 1944. This would not have been a major undertaking for the European Theater of Operations, but movement to CBI was complicated by the long distance from the United States, the poor state of communications within the theater, and the low priority of CBI, especially with regard to shipping. The proviso at Sextant that Matterhorn shipments not materially affect other approved operations in CBI conflicted with the tight timetable and had to be disregarded.^[87][26]

High priority passengers and freight traveled by air. The Air Transport Command (ATC) ran a route via Natal, Khartoum and Karachi. The trip could take as few as six days, but personnel were often bumped from flights in favour of more important passengers, and many took over a month. The advance party of the XX Bomber Command, which included Wolfe, left Morrison Field in twenty C-87 transports on 5 January 1944 and arrived in New Delhi eight days later.^[88] Wolfe established his headquarters at Kharagpur, which was situated at a junction on Bengal Nagpur Railway lines serving the airfields. The Hijli Detention Camp was taken over to serve as his headquarters building.^[87]

It was originally intended that all air crews, both regular and relief, would fly in B-29s, but this was discarded in favor of carrying a spare engine in each plane in lieu of passengers. A sea-air service was instituted, sailing from Newark, New Jersey, to Casablanca, and then by air to Karachi. Twenty-five Douglas C-54 Skymaster aircraft were assigned to this service, which ran from 8 April to 1 June, and carried 1,252 passengers and 250 replacement Wright R-3350 engines. Stilwell provided this from CBI's allotment of ATC flights.^[88]

Cargo ships usually went to Calcutta and troop ships to Bombay, which was safer. The ports of India were congested and inefficient. Allied shipping losses had been lower than anticipated in the second half of 1943, so more cargo ships were available. By 19 February 1944, 52,000 short tons (47,000 t) of supplies were en route to CBI. Troopships were harder to find. Ships bound for CBI went via the Pacific, sailing south of Australia, or the Atlantic via the Mediterranean Sea and the Suez Canal. A Liberty ship took about sixty days to make the voyage from the United States to India, and the ports there were overburdened and inefficient, so it could only make two round trips per year.^[88]

A contingent that included seven of the bomb maintenance squadrons departed from Newport News on 12 February with a Liberty ship convoy to Oran. From there they were taken to Bombay on the liner SS Champollion, which they reached on 1 April. Other units sailed from Casablanca on the Dutch liner SS Volendam on 22 February, and reached Bombay on 25 April. Eight bomb maintenance squadrons embarked from Los Angeles on the troopship USS Mount Vernon on 27 February. Sailing via Melbourne, Australia, they reached Bombay on 31 March. From there it took a week to travel across India to Kharagpur by train. One contingent made the trip from the United States to Kharagpur in 34 days, but most took eight to ten weeks.^[88][89][90]

On 10 May, the XX Bomber Command reported 21,930 personnel on hand. This included a few who were already stationed in CBI, and several hundred who had arrived by air, but about 20,000 of them had arrived by sea in March and April.^[88]

B-29 deployment

The construction of airfields in China and India with unusually long runways could not be concealed from the Japanese. Nonetheless, the B-29 Hobo Queen, commanded by Colonel Frank R. Cook, flew to RAF Bassingbourn in the UK on 8 March as part of a deception plan that the B-29 would be deployed to Europe. It departed the UK on 1 April, and became the second B-29 to reach its destination when it touched down at Kharagpur on 6 April;^[91][92] the first, Gone With the Wind, piloted by Harman, reached Chakulia on 2 April.^[91][93] The B-29s of the 58th Bombardment Wing began departing for India on 24 March, setting out in daily increments of nine or ten aircraft, with the trip expected to take up to five days. The chosen route was from Salina to Gander Lake (2,580 miles, 4,150 km), Marrakech (2,700 miles, 4,300 km), Cairo (2,350 miles, 3,780 km), Karachi (2,400 miles, 3,900 km) and Calcutta (1,500 miles, 2,400 km), a total of 11,530 miles (18,560 km).^[91] Air crew were not informed of their final destination before departure.^[93]

By 15 April, only 32 aircraft had arrived at their stations. One B-29 crashed on takeoff from Marrakesh after the pilot forgot to extend the flaps. Another was grounded in Cairo for two weeks while engineers replaced all four engines. Two were lost in Cairo; one developed engine trouble soon after takeoff and crashed and burned on landing when it attempted to land, while another crashed on landing when its nose landing gear collapsed. All the crewmen survived these accidents, but five died when a B-29 crashed in Karachi in a sandstorm. Another was also lost there, and all B-29s were grounded from 21 to 29 April while investigations were conducted into the causes.^[91][94] In all, five B-29s were lost and four damaged en route, but 130 aircraft had arrived safely by 8 May.^[d] Wolfe reported to Arnold on 26 April 1944 that: "The airplanes and crews got off to a bad start due to late production schedules, difficult modifications, inclement weather, and the sheer pressure of time necessary to meet the early commitment date."^[95]

Fighters

The deception plan was a failure; the Japanese made it known through radio broadcasts that they were well aware of the deployment of the B-29s. Although Calcutta was bombed, the B-29 airfields in Bengal lay close to the limit of the range of Japanese bombers. The airfields around Chengdu were well within range though. For this reason Chennault had asked for a fighter group to defend the airfields, and the Matterhorn plan had called for two. At the Sextant Conference the Combined Chiefs of Staff had decided to transfer two fighter groups from Italy.^[98]

The 33rd and 81st Fighter Groups were selected. To control the fighters, the Fourteenth Air Force activated the 312th Fighter Wing on 13 March, and Brigadier General Adlai H. Gilkeson assumed command twelve days later. Chennault recommended that the groups be equipped with North American P-51 Mustang fighters, but they had to be equipped with the less fuel efficient Republic P-47 Thunderbolt. Stratemeyer asked that the P-47s be sent from the United States, and the two groups conduct their conversion training in CBI.^[98]

If shipped normally, they would not arrive in Karachi before May, so the U.S. Navy made the escort carriers USS Mission Bay and Wake Island available to deliver the first hundred P-47s; the remaining fifty followed on freighters. The deployment of the two groups was delayed by their participation in the Battle of Anzio, but their flight echelons moved by air in mid-February, and the ground echelons moved by sea, embarking from Taranto, and arriving at Bombay on 20 March. The P-47s arrived at Karachi on 30 March, allowing conversion training to commence.^[98]

Stilwell was sufficiently concerned about the security of the Chengdu airfields to recommend that B-29 operations be postponed by a month. Permission for this was not forthcoiming, so the 33rd Fighter Group's 59th Fighter Squadron was sent to Sichuan with its old P-40s. It provided Chengdu's sole air defense until May, when the rest of the 33rd Fighter Group, the 58th and 60th Fighter Squadrons, arrived with their P-47s. The 81st Fighter Group's 92nd Fighter Squadron deployed to Guanghan on 15 May, but the 91st and 93rd Fighter Squadrons did not join it until July. In the event, the Japanese response was not as intense as had been feared, and the late deployment of the fighters eased the burden of sticking fuel at Chengdu.^[98]

Logistics

The XX Bomber Command was well-situated in India, enjoying good road and rail communications with the port of Calcutta, the 28th Air Depot at Barrackpore, the ATC terminus in Assam, and the Air Service Command installations at Alipore. But delays in stocking the bases in China upset the Matterhorn timetable. Supplies moved from the port at Calcutta to Assam by rail and barge, from whence they had to be flown across the Hump. Although a key feature of the Matterhorn plan was that the XX Bomber Command would support itself, this was soon revealed to be impractical, and it had to fall back on the services of Brigadier General Thomas O. Hardin's India–China Wing (ICW) of the ATC. This generated friction with the Fourteenth Air Force, which saw the XX Bomber Command as an interloping freeloader.^[99]

The twenty C-87s that the XX Bomber Command brought with it had been flown out by ATC pilots on 90-days' temporary duty. They were intended to be operated by pilots of Stratemeyer's 308th Bombardment Group, but Stratemeyer objected. Instead the nineteen C-87s (one having been lost en route) were turned over to the ATC in return for an all the temporary-duty ATC pilots continued to fly them until they had to return to the United States, after which the C-87s were turned over to the XX Bomber Command. The ICW promised that the XX Bomber Command would receive 1,650 tons out of the first 10,250 short tons (9,300 t) flown over the Hump in February, plus half of the next 1,250 short tons (1,130 t), a possible total of 2,275 short tons (2,064 t), assuming that the ATC could meet its target. As it happened, the ATC exceeded its target, and delivered 12,950 short tons (11,750 t), but Wolfe handed 1,534 short tons (1,392 t) over to Chennault and the XX Bomber Command received just 400 short tons (360 t).^[99]

March was a difficult month for the ICW, with a gasoline shortage in Assam. The opening of the Battle of Imphal and operations in Northern Burma and Western Yunnan caused both ATC aircraft and 682 short tons (619 t) of supplies intended for Matterhorn to be diverted to support of the ground forces. In April the C-46s only managed to haul a meager 14 short tons (13 t) to China.^[101] The first two B-29s flew across the Hump with gasoline on 26 April.^[102] One, flown by Major Charles Hansen, was attacked by six Japanese Nakajima Ki-43 Hayabusa (Oscar) fighters. Hansen's crew were was credited with downing one of the fighters; one crewman was wounded. In turn, they claimed to have shot him down, but all the aircraft involved landed safely.^[103][104] B-29s delivered 27 short tons (24 t) that month. A B-29 combat sortie was estimated to require 23 short tons (21 t), so this was sufficient to support one combat sortie. Wolfe calculated that he needed 4,600 short tons (4,200 t) to support two 100-bomber raids on Japan.^[105]

Arnold assigned three squadrons with eighteen Curtiss C-46 Commando each to support Matterhorn. The first C-46 reached Bengal on 10 April. One squadron was assigned to the Hump run while the other two, designated the 1st and 2nd Air Transport Squadrons (Mobile), joined the ATC's North African Wing. They lacked the range of the C-54s and had to make more stopovers, but they hauled 333 short tons (302 t) per month in June and July, which included 225 spare Wright R-3350 engines. Matterhorn was also allocated 50 short tons (45 t) per month from the weekly ATC "Fireball" service to CBI,^[88] which flew in urgently required spare parts from the Fairfield Aviation General Supply Depot in Fairfield, Ohio.^[106]

The ICW delivered 1,293 short tons (1,173 t) in May. Wolfe had some B-29s converted to tankers by stripping them of combat equipment except for the tail guns. In this configuration, a B-29 could carry seven tons instead of three. On 26 May, the Japanese launched an offensive in China. Stilwell diverted diverted Hump tonnage earmarked for Matterhorn to the Fourteenth Air Force, and forwarded a request from Chiang that the XX Bomber Command's stockpiles in China be handed over to the Fourteenth Air Force to the JCS, but without his endorsement. The JCS declined the request.^[108] The 2nd and 3rd Air Transport Squadrons were reassigned from the North African Wing to the XX Bomber Command. The former was assigned to the Hump run in June followed by the latter in July. The allocation to the 312th Fighter Wing was again cut, but on 20 July responsibility for its maintenance was handed over to the Fourteenth Air Force, along with its 1,500-short-ton (1,400 t) monthly Hump tonnage allocation.^[109]

Lieutenant Colonel Robert S. McNamara's statistical section of the XX Bomber Command conducted a detailed investigation of the different factors involved in the delivery of supplies to China. He managed to reduce gasoline consumption on a B-29 round trip to China from 6,312 US gallons (23,890 L) in May to 5,651 US gallons (21,390 L) in July, while the fuel it delivered rose from 495 US gallons (1,870 L) to 1,326 US gallons (5,020 L), and each B-29 tanker delivered 2,496 US gallons (9,450 L). In July, 237 B-29 trips and 419 C-46 trips delivered 1,162 short tons (1,054 t) in C-46's,^[109] 1,063 short tons (964 t) in tactical B-29s, and 2,998 short tons (2,720 t) in B-29 tankers. The XX Bomber Command also received 976 tons from the ATC, for a total of 3,954 tons.^[110]

Part of this was accomplished by flying a more southerly and direct route. This brought the B-29s in range of Japanese fighters based in northern Burma, but there were only seven contacts with Japanese fighters, and no attacks were pressed. The Hump was still dangerous, though, with high mountains and variable weather, and flights were counted as combat missions for the purpose of crew rotation. Twelve B-29s were lost over the Hump route by the end of July, mostly due to engine failures, and six C-46s by the end of September. Most of the crews were rescued by friendly Chinese civilians.^[109]

In September 1944 70 C-109s were added to the effort, flown by surplus B-29 crews, but XX Bomber Command, fearful of diversions to other agencies, resisted all attempts to have them operated by ATC. Its transport procedures contradicted those of ATC, however, limiting its efficiency, and beginning in November 1944 the B-29s were withdrawn from the airlift and the C-109s transferred to ATC.^[111]

Operations

Bangkok

By 19 May the XX Bomber Command had accumulated 2,867 flying hours in B-29s, of which 2,378 were on transport missions and 50 on miscellaneous tasks. Only 439 had been devoted to training activities. Since there were 240 crews, this worked out to less than two hours each. Before attempting a raid on Japan, Wolfe decided to conduct a shakedown combat mission. The chosen target was the Makkasan railway yard facilities in Bangkok, Thailand.^[53] This was the only heavy locomotive and railway car repair shop on the Burma-Thailand railway network. A successful attack could affect the supply of Japanese troops fighting around Imphal and Myitkyina. Intelligence indicated that the likely Japanese anti-aircraft and fighter opposition would not be as great as that anticipated over Japan.^[113] The decisive factor in the choice of target, though, was that it could be attacked from the airfields in Bengal and would not affect the supplies stockpiled in Chengdu.^{[53][113][114]}

The mission involved a round trip of 2,261 miles (3,639 km).^[114] Each bomber carried a fuel load of 6,846 US gallons (25,910 L) and 5 short tons (4.5 t) of bombs; three groups carried 500-pound (230 kg) general-purpose bombs while the fourth carried M18 incendiary bombs.^[53] The XX Bomber Command wanted to test out the new M18 incendiary bombs and the large number of wooden buildings and freight cars and a small oil facility in the area offered good targets.^[113] The resulting 134,000-pound (61,000 kg) takeoff weight was too heavy for the temporary field at Charra, so the 444th Bombardment Group had to stage from the other three fields.^[53] The attack was launched at 05:45 (local time) on 5 June 1944 to avoid high ground temperatures that were bad for the R-3350 engines and to allow the whole mission to be conducted in daylight. Wolfe had suggested a night-time raid, but Arnold insisted on daylight precision bombing.^[113][115]

Of the 112 bombers that were readied for the mission, 98 took off from India.^[113] It took sixty-three minutes to get them all in the air.^[115] Most of the bombers that failed to take off had ignition or supercharger problem. One plane crashed shortly after takeoff when an engine lost power, killing all on board except the co-pilot.^[116][117] Thirteen planes aborted. Twelve aborted due to mechanical failures, most of which involved oil leaks or faults with the oil coolers. One plane failed to find its formation as a tropical cyclone rolled in over the Bay of Bengal; several others joined formations of groups other than their own, and some proceeded on their own.^[116][115]

Seventy-seven planes found the target. Seven planes reached Bangkok but were unable to bomb due to mechanical problems. Six had problems with their bomb bays. A chaotic series of bombing runs were made between 10:52 and 12:32. Because the target was obscured by clouds, forty-eight planes bombed by radar, although most crews had not been instructed in this technique. Japanese anti-aircraft fire was inaccurate, and although nine fighters attacked the bombers, thei attacks were not pressed, and no B-29s were shot down.^[118][115] Four planes were lost on the return trip; two ditched into the Bay of Bengal after fuel ran out due to problems with the fuel transfer system; one crashed attempting to land at Dum Dum airfield; and one diverted to Kunming, China, but ran out of fuel and the crew had to bail out.^[119][120]

The mission to Bangkok resulted in the loss of five B-29s and the deaths of fifteen aircrew, with two more missing. Photo reconnaissance on 8 June indicated that sixteen or eighteen bombs had fallen within the target area. There was some damage to rolling stock and buildings, including the erecting and boiler shops. It was assessed that the damage would have no impact on the Japanese forces in Burma. The XX Bomber Command rated the mission as a success.^[121][122]

Yawata

The following day Wolfe received orders from Arnold for an attack Japan with at least 70 B-29s on 15 June, to coincide with the invasion of the Marianas. Drastic economies were applied, which particularly affected the 312th Fighter Wing, which was left with very little fuel. Wolfe calculated that he would have enough fuel for a raid, but not enough for all the B-29s to return to India immediately afterwards. A particular problem was that only 86 Superfortreses could be equipped with the bomb bay tanks needed for the flight to Japan.^[108][122] The B-29s began staging to China on 13 June. Each carried a full bomb load of eight 500-pound (230 kg) general purpose bombs, so only refueling was required in China. Of the 92 Superfortresses that departed, 79 made it to Chengdu, and one crashed en route.^[123]

The target chosen for the mission was the Imperial Iron and Steel Works in Yawata, which produced an estimated 2,250,000 metric tons of steel annually, representing 24 percent of Japan's steel output. This production was dependent on three coke plants, the largest of which, with an annual production of 1,784,000 metric tons, was designated the aiming point for the raid.^[124][123] It was a 3,182-mile (5,121 km) round trip from Chengdu to Yawata.^[125] In the belief that the B-29 lacked the range to fly there in a combat formation, Arnold authorized a night attack, with the planes bombing individually by radar.^[124] The raid on Yawata was the first on the Japanese home islands since the Doolittle raid of April 1942 and marked the beginning of the strategic bombardment campaign against Japan.^[126] Eight journalists and three news photographers accompanied the mission,^[127] which was led by Saunders, who flew as a passenger on B-29 Superfortress 42-6274 Lady Hamilton of the 468th Bombardment Group, piloted by Engler.^[128][129]

Takeoffs began at 16:16 local time. One plane crashed on takeoff but the crew escaped. Not so lucky were the crew of another which was launched after the main group to conduct post-attack photography that also crashed on takeoff; the whole crew died. Four planes aborted the mission and returned to Chengdu.^[127][128] Only forty-seven of the sixty-eight B–29s launched hit the target area: one crashed en route, six jettisoned their bombs because of mechanical difficulties, and seven bombed secondary targets or targets of opportunity.^[130] Six bombers suffered minor damage from flak, and one was lost over Yawata, 42-6230 Limber Dragon, which was shot down by a Kawasaki Ki-45 night fighter piloted by Warrant Officer Sadamitsu Kimura. One Japanese fighter reported minor damage.^[131]

On the way back to Chengdu, two B-29s crashed into mountainsides in China with the loss of all on board, including Newsweek correspondent William T. Shenkel. Another, with Time-Life photographer Harry Zinder on board, was strafed and destroyed by Japanese aircraft after making an emergency landing on the grass airstrip at Neixiang.^{[131][132][133]} To get his B-29s back to India, Wolfe had to borrow 15,000 US gallons (57,000 L) from the 312th Fighter Wing's meager supply. Although B-29s sat on the ground at Chengdu unprotected for several days afterwards, there were no Japanese attacks on the bases at Chengdu.^[130]

The raid on Yawata cost seven B-29s and fifty-five crewmen. Photos of the target were taken by the Fourteenth Air Force on 8 June, which indicated that only one bomb had landed in the target area, striking a power house 3,700 feet (1,100 m) from the coke ovens.^[130] Press releases were factual and downplayed the damage inflicted. The existence of the Twentieth Air Force and XX Bomber Command were disclosed for the first time.^{[134][129][135]}

Sasebo

Arnold ordered a small fifteen-plane follow-up raid on Japan by 10 July to demonstrate that Yawata was the start of a bombing campaign and not a one-off like the Doolittle raid, followed by a hundred-plane attack on Manchuria by 30 July and a fifty-plane attack on Palembang as soon as the airfields in Ceylon were ready. Wolfe's response was a counterproposal, scaling back the size of the forces to be engaged. Arnold relieved Wolfe of his command on 4 July, and promoted him to major general. Saunders assumed temporary command until Wolfe's relief, Major General Curtis E. LeMay, could arrive.^[136][137]

The first of the requested missions was flown on the night of 7 July. The mission plan called for attacks on five targets on Kyushu: eighteen bombers would attack the Sasebo Naval Base; three would bomb the Akunoura engine works in Nagasaki; two would raid the nearby Omura aircraft plant; and one-plane strikes would be conducted against the steel works at Yawata and Tobata. That the likely damage would be negligible was not overlooked, but it was felt that this would be outweighed by the psychological factor. Putting 25 B-29s over Japan required 203 Hump missions and ate into the stockpile required for the hundred-plane mission to Manchuria.^[138]

Of the 28 B-29s despatched from India, two had to turn back with mechanical trouble.^[139] One plane caught fire on the ground at Chakulia and was a total loss.^[100][140] Seventeenth planes took off from Chengdu, along with two reconnaissance aircraft detailed to photograph the Miike Dyestuffs Plant in Omuta. Eleven bombed Sasebo using radar, as cloud cover obscured the target. Single planes attacked Omura and Tobata; one plane bombed Laoyao harbor near Yawata; and another bombed Hankou, but missed the city by 20 miles (32 km).^{[136][141][142]} No planes were lost to flak or fighters over Japan, but one ditched into the sea.^[143][140]

Anshan

With 3,954 short tons (3,587 t) carried across the Hump in July, the availability of aircraft now became the major limiting factor on operations. With only 127 B-29s available after some had been converted to tankers, Sanders was hard pressed to meet the Arnold's desire for a 100-plane strike. To gather as many aircraft as possible, he pushed back the date for the operation to the end of July. This meant postponing Palembang until August, but the airfields on Ceylon were not yet ready in any case. By allocating five days for the deployment to China, aircraft that were forced to turn back could be repaired and sent out again, and additional maintenance could be performed in China. The procedure entailed some risk because the B-29s could become targets for Japanese attacks while sitting on the ground at Chengdu for up to five days.^[110][144]

The B-29s began making the trip to China on 25 July, and only four of the 111 despatched failed to reach China. One aircraft's engine caught on fire after takeoff for Chakulia, and it crash landed near Midnapore; nine of the thirteen crew died.^[110][145] The mission was launched on 29 July. The target was the Showa Steel Works in Anshan, an important producer of coke, pig iron and steel. It produced 3,793,000 metric tons of coke annually, about a third of the Japanese Empire's total. The 444th Bombardment Group's base at Guanghan Airfield was rendered unserviceable by heavy rains, but 79 B-29s from the other three groups were available, and all but seven were able to take off. On crashed shortly afterwards when two engines caught fire.^[146][147]

Eleven aircraft developed mechanical trouble, and did not reach the target. One bombed the bombed the secondary target, the port of Qinhuangdao, two bombed the target of last resort, rail yards at Zhengxian, four attacked targets of opportunity, and four returned without bombing at all. Sixty attacked the Showa Steel Works, flying in close formation. A bomb hit a byproducts plant near the target, resulting in a cloud of dark smoke.^[148][149]

Flak damaged five bombers. One, Lady Hamilton, was then shot down by fighters. Eight of the crew bailed out and eventually reached Chengdu with the aid of Chinese guerrillas.^[148][149] Another made an emergency landing at Ankang. The Japanese attempted to destroy it on the ground while it sat there for five days, resulting in the loss of a Kawasaki Ki-48 bomber during a night raid to Fourteenth Air Force fighters. Tools, spare parts and mechanics were flown in by C-46 and the B-29 was repaired and took to the sky again on 3 August.^[148][150] Flak damaged one of the engines of Ramp Tramp, so it made an emergency landing in Vladivostok. The crew were interned in the Soviet Union, but were permitted to escape to Iran, along with the crews of three other B-29s that landed in the Soviet Union. The Soviets later reverse engineered the B-29 to produce the Tupolev Tu-4.^[149]

The ground at Guanghan dried out, allowing twenty-four B-29s of the 444th Bombardment Group to take to the air. It was five hours too late to participate in the attack on Anshan, so they headed for the tertiary target, the port of Taku. Five planes turned back with mechanical trouble, sixteen planes bombed Taku, and three attacked Zhengxian.^[148][150]

The mission was assessed as a success. At a cost of five B-29s, there were direct hits on two of the sixteen coke oven batteries and damage to a third, which was estimated would take a year to repair. At Taku two large warehouses and a collier were damaged.^[148][150]

Palembang

The Pladjoe refinery at Palembang was the source of 22 percent of Japan's fuel oil for ships and industrial facilities, and 78 percent of its aviation gasoline, and was therefore a major target for the B-29s. Arnold wanted a 112-plane raid, but with only the airfield at China Bay available, a 50-plane raid was the best that Saunders could do. The mission was the longest flown from CBI. It had two targets: in addition to the attack on the refinery, fourteen B-29s of the 462nd Bombardment Group were detailed to drop Mark 26 1,000-pound (450 kg) aerial mines in the Moesi River. This was the first use of aerial mines by the Twentieth Air Force.^[151][152] This mission involved a flight of 3,855 miles (6,204 km) to Palembang and 4,030 miles (6,490 km) to the Moesi River, so maximum fuel loads were carried, which meant only a one short ton (0.91 t) of bombs or mines.^[153]

Fifty-six B-29s of 444th and 468th Bombardment Groups arrived at China Bay on the afternoon of 9 August.^[154][155] The strike force began to take off from China Bay at 16:45 the next day. A total of 54 B-29s were dispatched. One of the aircraft returned to the base 40 minutes after taking off due to engine problems, it was repaired within two hours, and took off again bound for Sumatra. Eight aircraft returned to Ceylon with mechanical trouble, and six more did not bomb the primary target. Thirty-nine bombers reached their primary targets. Thirty-one attacked the refinery. The B-29 assigned to drop illumination flares did not make it, so bombing was at night through overcast. A photo reconnaissance mission could not be flown until 19 September, which made it difficult to assess the results, but it appeared than only one building had been destroyed.^[156][157]

Carmichael personally led the 462nd Bombardment Group's mining mission^[152] Eight bombers carried out the mission, laying sixteen aerial mines.^[156] Mines dropped in the river connecting Palembang to the sea sank three ships totalling 1,768 deadweight tons (1,796 deadweight tonnes) and damaged four ships of 6,560 deadweight tons (6,670 deadweight tonnes). It took the Japanese almost a month to sweep the mines and open the river was cleared for maritime traffic again, which held up petroleum exports.^[158] The Japanese fighters and antiaircraft guns failed to destroy any of the American bombers,^[157] but B-29 Superfortress 42-24420 of the 444th Bombardment Group ditched when it ran out of fuel 90 miles (140 km) from Ceylon.^{[159][160][161]} One crewman died, but the rest were rescued on 12 August by the British destroyer HMS Redoubt, which homed in on their Gibson Girl beacon.^[157][161]

This was the only USAAF raid on the oil facilities at Palembang. No more B-29 missions were flown from Ceylon. On 24 August, the XX Bomber Command recommended that the base at China Bay be abandoned, and Twentieth Air Force concurred on 3 October.^[157]

Nagasaki

Only using fifty-six B-29s against Palembang left aircraft available for use elsewhere. Saunders therefore proposed a small raid on Japan. It was hoped that striking on the same day as Palembang would have a psychological impact by demonstrating that the B-29s could simultaneously attack targets thousands of miles apart. Saunders chose Nagasaki as the target, as it was an important shipbuilding, steel and munitions production area. He proposed to attack at night with incendiaries. This was the first incendiary raid on Japan.^[162][163]

Thirty-three B-29s from all four groups took off from India. One had top turn back with mechanical problems and another caught fire and the crew had to bail out over India. Twenty-nine bombers took off for Nagasaki. Each B-29 carried thirteen M-18 incendiary clusters and three M-26 fragmentation clusters, a total load of 5,816 pounds (2,638 kg). Two bombers from the 40th Bombardment Group had to return early, one with an oil leak and one with radar problems. Twenty-six B-29s attacked the target. The damage inflicted was minimal.^[164][163]

No B-29s were lost over the target and one downed a Japanese fighter, the Twentieth Air Force's first confirmed kill. Two B-29s were lost due to running out of fuel. The crew of one bailed out over China; the other landed at a forward airfield where it sank into the mud. The 312th Fighter Wing provided air cover and mechanics were flown in. The Chinese jacked the plane up and laid 4,500 railroad ties. Mechanics and the crew stripped the aircraft of non-essential equipment, and it was able to take off again on 23 August and land at Chiung Lai.^[164][163]

Yawata II

For the next mission, Saunders wanted to complete the destruction of the coke oven in Yawata. His staff debated whether the best course of action was daylight precision bombing or a night attack with incendiaries. In the end, it was decided to do both, although not by design. One innovation was to allow the group commanders to set different loads for each B-29, based upon the efficiency of the aircraft and crew. On this mission some B-29s burned as little as 6,100 US gallons (23,000 L) and some as much as 7,600 US gallons (29,000 L), carrying an average of 6.3 500-pound (230 kg) bombs.^[165][166]

Three bombers had to return to India with mechanical trouble, two more had to land at forward airbase en route, and one crashed; the crew bailed out and were recovered by Chinese civilians. The three bombers that returned to base and one of the ones that made a forced landing were repaired and were able to rejoin the others in China. Ninety-seven bombers were then available in China, and seventy-five took off on the daylight raid. The eighth aircraft of the 462nd Bombardment Group to take off from Kuinglai crashed when its landing gear failed on takeoff, blocking the runway for the remaining thirteen aircraft. Strong winds prevented takeoff in the opposite direction, and it took six hours to clear the runway. It was therefore decided to mount a night mission. Eight of the thirteen remaining bombers were able to launch on this mission. They were joined by five bombers from the 40th and 444th Bombardment Groups that had failed to take off on the daylight raid, and one that had returned with mechanical trouble but had been repaired.^[167][168]

Sixty-one of the seventy-five bombers on the daylight raid found the target. They were met by intense flak from up to 166 anti-aircraft guns. Eight bombers were damaged and one, B-29 Superfortress 42-6408 Reddy Teddy of the 468th Bombardment Group, was shot down over Japan.^[169][170] Another, B-29 Superfortress 42-6308 Feather Merchant of the 40th Bombardment Group, was damaged by flak and fighters; all but two of the crew bailed out over friendly territory in China and were rescued by Chinese civilians.^[169][171] B-29 Superfortress 42-24474 Starduster of the 462nd Bombardment Group, piloted by Carmichael, was damaged by a Japanese Ki-45 fighter and crashed on Iki Island. Nine of the ten crew bailed out, but one man's parachute did not open and another was machine gunned in the air. The remaining seven, including Carmichael, were captured and endured beatings and mistreatment in captivity.^[172][173] B-29 Superfortress 42-93829 Cait Paomat received flak damage over Yawata and the pilot, Major Richard McGlinn, elected to bail out over the Soviet Union rather than Japanese-occupied China. The crew of eleven becames the second B-29 crew interned in the Soviet Union.^[172][174] That night ten more B-29s dropped bombs on Yawata. The damage assessment was dispiriting; two coke ovens had been hit. Four B-29s had been shot down and ten lost to other causes, and ninety-five aircrew were dead or missing. ^[175]

Anshan II

On August 20, LeMay arrived to breathe new energy into the XX Bomber Command. The former Eighth Air Force group and wing commander had achieved remarkable success with strategic bombing operations in Europe, testing new concepts such as stagger formations, the combat box, and straight-and-level bombing runs. The youngest two-star general in the Army Air Forces had also revised tactics, tightened and expanded formations, and enhanced training for greater bombing precision. He inaugurated a lead-crew training school so that formations could learn to drop as a unit on cue from the aircraft designated as the lead ship. During his first two months at XX Bomber Command, LeMay had little more success than Wolfe or Saunders. The command continued to average only about one sortie a month per aircraft against Japan's home islands. When Douglas MacArthur invaded the Philippines in October 1944, LeMay diverted his B-29s from bombing Japanese steel facilities to striking enemy aircraft factories and bases in Formosa, Kyūshū, and Manchuria.^[176]

LeMay gained the support of Communist leader Mao Zedong, who controlled parts of northern China. Willing to help against a common enemy, Mao agreed to assist downed American airmen and to locate in northern China a weather station that would provide better forecasts for the XX Bomber Command's raids on the Japanese in Manchuria and Kyūshū. Hoping to gain American recognition of his regime, Mao suggested that the Americans set up B–29 bases in northern China like those in Chiang Kai-shek's area of control in Sichuan. LeMay declined because he found it difficult enough to supply the airfields at Chengdu.^[176]

Ichi-Go and the first "fire raid" of Hankou (Wuhan)

In late 1944, the Japanese offensive Operation Ichi-Go in China probed toward the B–29 and Air Transport Command bases around Chengdu and Kunming. To slow the enemy advance, Maj. Gen. Claire L. Chennault of the Fourteenth Air Force asked for raids on Japanese supplies at Hankou (an area now part of present-day Wuhan), and the Joint Chiefs directed LeMay to hit the city with firebombs. On December 18, LeMay launched the fire raid, sending eighty-four B–29s in at medium altitude with five hundred tons of incendiary bombs. The attack left Hankou burning for three days, proving the effectiveness of incendiary weapons against the predominantly wooden housing stock of the Far East.^[176][177]

By late 1944, American bombers were raiding Japan from the recently captured Marianas, making operations from the vulnerable and logistically impractical China bases unnecessary. In January 1945, the XX Bomber Command abandoned its bases in China and concentrated 58th Bomb Wing resources in India. The transfer signaled the end of Matterhorn. During the same month, LeMay moved to the Marianas, leaving command of the XX Bomber Command in India to Brig. Gen. Roger M. Ramey. Between January and March, Ramey's B–29s assisted Mountbatten in the South-East Asian theatre, supporting British and Indian ground forces in Burma by targeting rail and port facilities in Indochina, Thailand, and Burma. More distant targets included refineries and airfields in Singapore, Malaya, as well as Palembang and other locations in the Netherlands East Indies. The 58th, the only operational wing of the XX Bomber Command, remained in India until the end of March 1945, when it moved to the Marianas to join the XXI Bomber Command.^[176]

XX Bomber Command stopped being an operational command at the end of March 1945 when the 58th Bomb Wing moved from India to the Marianas and control of the wing passed to the XXI Bomber Command.^[176]

Combat missions

Assessment

The American Bomber Summary Survey states that "Approximately 800 tons of bombs were dropped by China-based B-29s on Japanese home island targets from June 1944 to January 1945. These raids were of insufficient weight and accuracy to produce significant results."^[179] The XX Bomber Command failed to achieve the strategic objectives that the planners had intended for Operation Matterhorn, largely because of logistical problems, the bomber's mechanical difficulties, the vulnerability of Chinese staging bases, and the extreme range required to reach key Japanese cities. Although the B-29s achieved some success when diverted to support Chiang Kai-shek's forces in China, MacArthur's offensives in the Philippines, and Mountbatten's efforts in the Burma campaign, they generally accomplished little more than the B-17s and B-24s of the Fourteenth, Fifth, Thirteenth and Tenth Air Forces.^[180]

Chennault considered the Twentieth Air Force a liability and thought that its supplies of fuel and bombs could have been used more profitably by the Fourteenth Air Force. The XX Bomber Command consumed almost 15 percent of the Hump tonnage per month during Matterhorn.^[180] Lieutenant General Albert C. Wedemeyer, who replaced Stilwell as the American senior commander in the China theater in October 1944,^[181] agreed. The two were happy to see the B–29s leave China and India. Yet, despite those objections, Matterhorn did benefit the Allied war effort. Using the China bases bolstered Chinese morale and, more important, it allowed the strategic bombing of Japan to begin six months before bases were available in the Marianas. The Matterhorn raids against the Japanese home islands also demonstrated the B–29's effectiveness against Japanese fighters and anti-aircraft artillery. Operations from the Marianas would profit from the streamlined organization and improved tactics developed on the Asian mainland.^[180]