Operation Matterhorn logistics

Operation Matterhorn was a military operation of the United States Army Air Forces in World War II involving the strategic bombing of industrial facilities in Japan, China and Southeast Asia by Boeing B-29 Superfortress bombers. The creation of bases for the B-29s in India, Ceylon and China and their maintenance was a logistical undertaking of enormous magnitude and difficulty.

The B-29s were based in India but staged through bases around Chengdu in China's Sichuan province. Operations were conducted from China because no other sites within range of Japan were in Allied hands in early 1944. 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 was called. All the fuel, ammunition and supplies used by American forces in China had to be flown in over the Himalayas.

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. In November 1944, American bombers began raiding Japan from the Mariana Islands, and the B-29s left the logistically difficult and increasingly vulnerable bases in China in January 1945.

Background
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 mi. 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. With its 141 ft wingspan, the B-29 was one of the largest aircraft of World War II. The $3 billion cost of design and production (equivalent to $0 billion today), far exceeded the $1.9 billion cost of the Manhattan Project, made the B-29 program the most expensive military project of the war.

The basing of the Superfortresses in China was raised at the January 1943 Casablanca Conference. No other locations within range of Japan were in Allied hands or expected to be in 1944. Support for the effort was through the port of Calcutta, which was estimated to be able to handle the additional 596,000 ST per month.

After the Japanese had cut the Burma Road in March 1942, the only line of communications with China was over "the Hump", as the air ferry route to China over the Himalayas was called. Until the Burma Road could be reopened by the ground forces, all the fuel, ammunition and supplies used by American forces in China had flown over the Hump.

The Matterhorn plan called for supplies to be flown from India to China in Consolidated B-24 Liberator bombers converted to Consolidated C-87 Liberator Express transport aircraft. 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.

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. Colonel Leonard F. Harman became his deputy. For his assistant chief of staff for operations (A-3), Wolfe secured Brigadier General LaVerne G. Saunders, who had been awarded the Navy Cross while in the Guadalcanal campaign. To control the B-29s, the 58th Bombardment Wing was activated on 21 June. 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.

Airbases
A team headed by Brigadier General Robert C. Oliver, the commander of the China-Burma-India Theater (CBI) Air Service Command, began inspecting potential sites for B-29 bases in August 1943. The B-29's 141 ft wing span was considerably wider than the 104 ft of the B-17, the next largest aircraft in the inventory, and a fully-laden B-29 weighed about 70 ST, nearly twice as much as a B-17. The Twentieth Air Force asked for B-29 runways to be 8,500 ft long and 200 ft wide, nearly twice the area of a 6,000 by 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 they accepted all but Bishnupur, for which Dudhkundi was substituted.

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 ft long and 150 ft wide. Lieutenant Colonel Kenneth E. Madsen was in charge of the construction of the air bases; Colonel William C. Kinsolving, a petroleum engineer, had the task of laying two 4 in pipelines to the airfields. They reported to Colonel Thomas Farrell, who headed the CBI Construction Service.

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. The CBI theater commander, Lieutenant General Joseph W. Stilwell, 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.

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 it was eventually reassigned. 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. Religious sensibilities meant that seven different types of rations had to be stocked.

Grading of the runways accounted for more than half of the 1,700,000 cuyd of the earth moved. New concrete was laid 10 in thick; existing runways were overlaid with 7 in 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 used 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. 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.

Although reports to USAAF headquarters frequently claimed that work was proceeding on schedule, that schedule was far behind the original plans. Works on the airbases were not completed until September. The decision in April to deploy the second wing of B-29s to the Marianas meant that only four groups would be deployed to CBI instead of the originally planned eight, so only the five original airfields were required. Delays in construction at Dudhkundi meant that Charra Airfield had to be used 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 $ million in ).

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. It was estimated that the Matterhorn bases would require 4,736,000 USgal of fuel in March 1944, 3,536,000 USgal in April and May, 7,027,000 USgal in June, 7,077,000 USgal in July and 10,608,000 USgal in August. Each airbase was provided with 1,470,000 USgal of storage.

A Shell Oil terminal at Budge Budge had a tank farm with a capacity of 500,000 oilbbl, of which 300,000 to 400,000 oilbbl 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 6 in pipeline from Budge Budge to Kharagpur, a distance of about 60 mi. The 707th and 708th Engineer Petroleum Distribution Companies arrived a few days later and were assigned the task of laying 4 in pipelines from Kharagpur to Chakulia via Dudhkundi and from Kharagpur to Piardoba, respectively. Each four-inch line was about 50 mi long.

A major obstacle was the Hooghly River, which had a tidal bore of up to 7 ft and a current that could reach 25 mph. Heavy pipeline clamps were attached every few joints to hold the pipe in position on the bottom. Laying 5000 ft 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.

Due to a shortage of standard pipe, Farell and Kinsolving decided to use thin, light-weight, "invasion-weight" pipe. Pipes were buried to prevent accidental or deliberate damage in densely populated areas. 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." 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.

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. In addition, there were five airstrips for fighters. 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.

At the Sextant Conference in Cairo, Roosevelt promised 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 $0 to $0 million in ), at least at the official rate of exchange; 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. "One more example", he wrote in his diary, "of the stupid spirit of concession that proves to them that we are suckers."

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 $0 million in ), although this included payment for other works in addition to the Chengdu airfields. Arthur N. Young, the American financial advisor to the Chinese government was critical of the U.S. Army's profligate spending. Price caps on materials were imposed used by contractors, but with limited success. It became necessary to fly banknotes over the Hump. Landowners were inadequately compensated for the loss of their land and the peasants who worked it were not compensated at all. 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. These grievances generated support for the Chinese Communist Party.

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. Construction work was supervised by Lieutenant Colonel Waldo I. Kenerson. Only fourteen U.S. Army engineers were assigned to the project. Their role was limited to drafting specifications, carrying out inspections and administering the work. The Chinese Military Engineering Commission controlled construction. Some 300,000 impressed laborers and 75,000 contract workers were employed on the project. 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.

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. Food and accommodation were provided by the Chinese War Area Service Corps. 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.

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. Farrell sent some small rock crushers and provided a detachment of engineers to install the fuel handling systems. Because the B-29 runways could not be brought up to standard, they were built to the full length of 8,500 ft to allow for an extra margin of safety. They were 19 in deep, with 52 hardstands for each. The accompanying fighter strips were 4,000 ft long, 150 ft wide and 8 to 12 in deep with 4 to 8 hardstands each. Structures totalling 19,000 square meters were built, and each base had an oil storage tank.

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. Over 300,000 cubic meters were used for the runways and taxiways. Workers collected them from the banks of the Min River. When this source became depleted, they waded into the freezing rapids and shoals to collect them from the riverbed. 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. Saunders landed the first B-29 at Guanghan on 24 April, where he was met by officials including Wolfe, Zhang, and Major General Claire L. Chennault, the commander of the China-based Fourteenth Air Force. All four airfields were completed by 10 May 1944.

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.

Airbase construction in Ceylon was a SEAC responsibility. When the Assistant Chief of the Air Staff, Major General Laurence S. 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 it had a 7,200 ft runway with hardstands, fuel pumps and accommodation for 56 B-29s.

Deployment
The Matterhorn plan called for 20,000 troops and 200,000 ST of cargo to be shipped from the United States to CBI between 1 January and 30 June 1944, followed by 20,000 ST 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.

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. 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.

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.

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 ST 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.

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 on the liner SS Champollion to Bombay, which was 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 (AP-22) 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.

Aircraft maintenance
The USAAF defined four levels of maintenance:
 * 1st echelon: Maintenance performed by the air crews of the combat unit. This typically involved routine servicing of aircraft and equipment, preflight and daily inspections, and minor repairs and adjustments.
 * 2nd echelon: Maintenance performed by the ground crews of the combat unit and air base squadrons. This typically involved the servicing of aircraft and equipment, periodic inspections, and simple adjustments, repairs, and replacements of parts.
 * 3rd echelon: Maintenance performed by service groups and subdepots. This involved repairs and replacements requiring heavy or bulky machinery and equipment requiring surface transport. This echelon performed repairs, salvage, removal and replacement of major unit assemblies that required specialized mechanics.
 * 4th echelon: Maintenance performed by air depots, such as the overhaul of engines and major unit assemblies.

Since it was intended that the XX Bomber Command would be self-sufficient, it would handle its own 1st, 2nd and 3rd echelon maintenance, leaving only 4th echelon work to be done by the CBI Air Service Command. The ground personnel were separated from the bombardment squadrons, and formed into sixteen maintenance squadrons. Two regular air service groups were assigned to the XX Bomber Command, the 25th and 28th Service Groups. They were shipped early to help establish the bases, but were delayed en route by six weeks and did not reach Bombay until May. On arrival, they were assigned to the Air Service Command until an appeal from Wolfe resulted in Stilwell reassigning them to the XX Bomber Command on 7 June.

The two groups were reorganized into four, with the 80th and 87th Service Groups being formed, so each of the bases in India had its own service group. In September, the sixteen maintenance squadrons were disbanded and the ground crews assigned to the air squadrons. There were now only twelve squadrons instead of sixteen, and the surplus personnel were used to fill out the service groups. Although there were sufficient numbers, there remained critical shortages in some military occupational specialty codes, particularly mechanics skilled in maintaining the temperamental Wright R-3350 Duplex-Cyclone engines.

Supplying the bases in China
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.

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 the 308th Bombardment Group, but Major General George E. Stratemeyer, the CBI Air Forces commander, objected to this arrangement. Instead, the nineteen C-87s (one having been lost en route) were turned over to the ATC in return for an undertaking that the temporary-duty ATC pilots continued to fly them until they had to return to the United States, after which the C-87s would be returned to the XX Bomber Command. The ICW promised that the XX Bomber Command would receive 1,650 tons out of the first 10,250 ST flown over the Hump in February, plus half of the next 1,250 ST, a possible total of 2,275 ST, assuming that the ATC could meet its target. As it happened, the ATC exceeded its target, and delivered 12,950 ST, but Wolfe handed 1,534 ST over to Chennault and the XX Bomber Command received just 400 ST.

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 ST 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 ST to China. The first two B-29s flew across the Hump with gasoline on 26 April. One, flown by Major Charles Hansen, was attacked by six Japanese Nakajima Ki-43 Hayabusa (Oscar) fighters. Hansen's crew 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. B-29s delivered 27 ST that month. A B-29 combat sortie was estimated to require 23 ST, so this was sufficient to support one combat sortie. Wolfe calculated that he needed 4,600 ST to support two 100-bomber raids on Japan.

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 ST per month in June and July, which included 225 spare Wright R-3350 engines. Matterhorn was also allocated 50 ST per month from the weekly ATC "Fireball" service to CBI, which flew in urgently required spare parts from the Fairfield Aviation General Supply Depot in Fairfield, Ohio. The ICW delivered 1,293 ST 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 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.

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 ST monthly Hump tonnage allocation.

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 USgal in May to 5,651 USgal in July, while the fuel it delivered rose from 495 USgal to 1,326 USgal, and each B-29 tanker delivered 2,496 USgal. In July, 237 B-29 trips and 419 C-46 trips delivered 1,162 ST in C-46's, 1,063 ST in tactical B-29s, and 2,998 ST in B-29 tankers. The XX Bomber Command also received 976 tons from the ATC, for a total of 3,954 tons. 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.

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 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 were transferred to the ATC.

End of Matterhorn
In late 1944, the Japanese Operation Ichi-Go offensive in China probed relentlessly toward the B–29 and ATC bases around Chengdu and Kunming. Meanwhile, on 24 November, American bombers commenced raiding Japan from the Mariana Islands, making operations from the increasingly vulnerable and always logistically difficult China bases redundant. In January 1945, the XX Bomber Command abandoned its bases in China and concentrated its resources in India. This marked the end of Operation Matterhorn.

On 6 February, the War Department issued orders for the B-29s to redeploy to the Mariana Islands. The 312th Fighter Wing was reassigned to the Fourteenth Air Force on 8 February, leaving the 58th Bomb Wing, which was reactivated on the same day, as the only operational wing of the XX Bomber Command. The first water echelon, consisting of 2,275 men, sailed from Calcutta on 27 February. They were followed by an advance air echelon on 20 March. Four cargo ships loaded with equipment departed between 25 March and 4 April. An air echelons of 90 aircraft carrying 1,330 airmen flew to Tinian in the Marianas via Lüliang on 20 April; a second, of another 90 aircraft and 1,620 airmen, flew to Guam on 1 May. The last water echelon, consisting of 3,459 men, left on 6 May. The last shipment arrived in the Marianas on 6 June. The whole movement was accomplished without the loss of a single aircraft.

Between June 1944 and January 1945, China-based B-29s dropped 800 ST of bombs on Japan. The post-war United States Strategic Bombing Survey (USSBS) judged that this was insufficient to make much of an impact. 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. The original aim of making the XX Bomber Command self-sufficient was overly optimistic: of the 41,733 ST of supplies delivered to Chengdu, only 14,517 ST were carried by the XX Bomber Command's planes; the other 217,216 ST were delivered by the ATC.