Operation Matterhorn

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

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

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

Support for the effort was through the

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

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

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

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

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

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

A settlement was reached between the

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.

Some 1,000 ox carts, 15,000 wheelbarrows and 1,500 trucks were used to carry building materials. There were no bulldozers,

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

High priority passengers and freight traveled by air. The

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

A contingent that included seven of the bomb maintenance squadrons departed from

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

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

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

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

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

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).

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

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

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

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

Main article: Operation Boomerang

The Pladjoe refinery at

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 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 to 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 became 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

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

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

Combat missions^[178]

Mission	Date	Primary target	Groups	Up	Bombed	Lost
1	5 June 1944	Makkasan railway yards, Bangkok, Thailand	40, 444, 462, 468	98	77	5
2	15 June 1944	Yahata Steel Works, Yahata, Fukuoka, Japan	40, 444, 462, 468	68	47	7
3	7 July 1944	Sasebo Shipyard, Nagasaki, Japan	444, 468	18	14	0
4	29 July 1944	Showa Steel Works, Anshan, Manchuria	40, 444, 462, 468	96	75	3
5	10 August 1944	Baraban oil refineries, Palembang, Dutch East Indies	40, 444, 462, 468	54	39	2
6	10 August 1944	Nagasaki, Japan	40, 444, 462, 468	29	24	1
7	20 August 1944	Yahata Steel Works, Yahata, Fukuoka, Japan	40, 444, 462, 468	88	71	14
8	8 September 1944	Showa Steel Works, Anshan, Manchuria	40, 444, 462, 468	88	72	3
9	26 September 1944	Showa Steel Works, Anshan, Manchuria	40, 444, 462, 468	109	83	0
10	14 October 1944	Takao Naval Air Station, Okayama, Formosa	40, 444, 462, 468	131	106	2
11	16 October 1944	Okayama, Formosa	444, 462	49	38	0
11	16 October 1944	Heito, Formosa	468	24	20
12	17 October 1944	Einansho Airfield, Tainan, Formosa	40	30	10	0
13	25 October 1944	Omura, Nagasaki, Japan	40, 444, 462, 468	75	58	0
14	3 November 1944	Malegon Railway Yards, Rangoon, Burma	40, 444, 462, 468	50	44	1
15	5 November 1944	Singapore	40, 444, 462, 468	74	53	3
16	5 November 1944	Omura Aircraft Factory, Nagasaki, Japan	40, 444, 462, 468	93	29	2
17	11 November 1944	Omura Aircraft Factory, Nagasaki, Japan	40, 444, 462, 468	96	63	2
18	27 November 1944	Bangkok, Thailand	40, 444, 462, 468	60	55	3
19	7 December 1944	Mukden , Manchuria	40, 444, 462, 468	70	40	9
20	14 December 1944	Rama VI Bridge, Bangkok, Thailand	40, 444, 462, 468	45	33	1
21	18 December 1944	Hankou, China	40, 444, 462, 468	94	85	6
22	19 December 1944	Omura, Nagasaki, Japan	40, 444, 462, 468	36	17	5
23	21 December 1944	Mukden , Manchuria	40, 444, 462, 468	55	40	0
24	2 January 1945	Rama VI Bridge, Bangkok, Thailand	40, 444, 462, 468	49	44	2
25	6 January 1945	Omura, Nagasaki, Japan	40, 444, 462, 468	48	29	2
26	9 January 1945	Formosa	40, 444, 462, 468	46	40	0
27	11 January 1945	Floating Dry Dock and King George VI Graving Dock, Singapore	40, 444, 462, 468	43	27	0
28	14 January 1945	Kagi Airfield, Chiayi County, Formosa	40, 444, 462, 468	82	54	0
29	17 January 1945	Shinchiku, Formosa	40, 444, 462, 468	90	78	2
30	25 January 1945	Mine-laying, Indochina area	462	26	25	0
31	25 January 1945	Mine-laying, Singapore area	444, 462	45	41	1
32	27 January 1945	Saigon Naval Shipyard	40	25	22	0
33	1 February 1945	Floating Dry Dock	40, 444, 462, 468	104	78	0
34	7 February 1945	Saigon Naval Shipyard	444, 462	66	44	0
34	7 February 1945	Phnom Penh, Indochina	444, 462		17	0
35	7 February 1945	Rama VI Bridge, Bangkok, Thailand	40, 468	60	59	2
36	11 February 1945	Rangoon , Burma	40, 444, 462, 468	60	56	1
37	19 February 1945	Kuala Lumpur, Malaya	444, 468	58	48	0
38	24 February 1945	Empire Dock, Singapore	40, 444, 462, 468	117	105	0
40	24 February 1945	Mine-laying, Johore Strait area	444	12	10	0
41	2 March 1945	Singapore Naval Base	40, 444, 462, 468	62	48	1
39	4 March 1945	Mine-laying, Yangtze River , China	468	30	24	0
43	10 March 1945	Railway yards, Kuala Lumpur, Malaya	468	29	23	0
42	12 March 1945	Samboe Island oil storage, Singapore	40	15	11	0
42	12 March 1945	Bukum Island oil storage, Singapore	444	30	21	0
42	12 March 1945	Sebarok Island oil storage, Singapore	462	15	11	0
44	17 March 1945	Rangoon , Burma	40, 468	39	39	0
45	22 March 1945	Rangoon , Burma	444, 462	30	28	0
45	22 March 1945	Mingaladon railway station, Rangoon, Burma	468	10	10	0
46	28 March 1945	Mine-laying, Yangtze River , China	468	10	10	0
47	28 March 1945	Mine-laying, Saigon area and Cam Ranh Bay , Indochina	468	18	16	0
48	28 March 1945	Mine-laying, Johore Strait and Riau Strait , Malaya	444	33	32	0
49	29 March 1945	Bukum Island oil storage, Singapore	40, 462	26	24	0

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.

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]

Footnotes

1. ^ The name "Superfortress" was not assigned until March 1944.^[2]
2. ^ ^{a b c d} The 395th, 679th, 771st and 795th Bombardment Squadrons were disbanded in October 1944.^[46][47]
3. ^ ^{a b c d} The bomb maintenance squadrons were disbanded in October 1944.^[46]
4. ^ By March 1945 another 255 B-29s had made their way to CBI, and only three were lost en route.^[95]
5. Charra Airfield until July, but that base was not capable of sustaining very heavy bomber operations.^[97]

Notes