马特霍恩作战

计划

马特霍恩作战计划最初是在1943年1月的卡萨布兰卡会议上被酝酿。美英联合参谋部于1943年8月在魁北克召开会议，决定在中太平洋采取夺占马里亚纳群岛的作战。不仅因为马里亚纳群岛靠近东京，而且容易补给与防卫。1943年9月，美英联合参谋部得出结论，在中国部署B-29轰炸机必须通过驼峰航线维持孤立的补给，这将招致后勤上的极大困难。但富兰克林·罗斯福总统坚持认为从中国轰炸日本能更快缩短战争进程。1943年底的开罗会议，罗斯福总统向蒋介石许诺将在中国部署战略轰炸机。亨利·阿诺德支持罗斯福总统的决定，认为中国的轰炸基地是在没有控制马里亚纳群岛之前的应急办法。
马特霍恩作战计划由Kenneth B. Wolfe准将于1943年10月制定，由第20轰炸航空队实施，代号“夕阳”（Setting Sun）。该计划是基于约瑟夫·史迪威的“暮光”（Twilight）计划。B-29的主基地设在印度，在中国开设前进基地并由驼峰航线的C-109运油机、20架C-87运输机、3架C-46运输机组成的支援中队维持补给。夕阳计划原定把前进基地设在广西。但由于豫湘桂会战失败，最终把B-29基地设在了成都。 最初计划由2,000架C-109支援在中国部署10个大队400架B-29，但由于马里亚纳群岛分担了战略轰炸任务，最终只把218架B-26轰炸机改装为C-109运油机。
阿诺德五星上将于1943年10月12日批准了“夕阳”计划并通过马歇尔将军提交给总统与参谋长联席会议。当时这是唯一的轰炸日本的作战计划。罗斯福总统不满该计划于1944年6月1日正式开始实施，而不是他向蒋介石保证的1944年1月1日。但罗斯福批准该计划将实施一整年。
B-29轰炸机的作战半径达到1,500英里（2,400千米），执行了轰炸日本的90%的任务。 

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Ichi-Go and the first "fire raid"

The former European theater bomber commander continued to experiment with new technologies and tactics and soon imported to China the incendiary weapons being used by the British against Germany. In late 1944,  a Japanese offensive (codenamed 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 Hankow, 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 Hankow burning for three days, proving the effectiveness of incendiary weapons against the predominantly wooden architecture of the Far East.
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.
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.

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." XX Bomber Command had 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 (see Operation Ichi-Go), 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-17 Flying Fortresses and B-24 Liberators assigned to the Fourteenth, Fifth, Thirteenth, and Tenth Air Forces.
Chennault considered the Twentieth Air Force a liability and thought that its supplies of fuel and bombs could have been more profitably used by his Fourteenth Air Force. The XX Bomber Command consumed almost 15 percent of the Hump airlift tonnage per month during Matterhorn. Lt. Gen. Albert C. Wedemeyer, who replaced Lt. Gen. Joseph W. Stilwell as American senior commander in the China theater, agreed with Chennault. The two were happy to see the B–29s leave China and India. Yet, despite those objections, Matterhorn did benefit the Allied 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.

指挥架构

General Arnold retained personal command of the Twentieth Air Force – to avoid diversion of assets from the B-29 effort against Japan, particularly by Admiral Nimitz, who was given command authority over all efforts in the Central Pacific – with Brigadier General Haywood S. Hansell as chief of staff (and later commander of XXI Bomber Command). Tentative plans called for an operational force of 48 B-29 groups, numbering between 1,000 and 1,500 B-29s, to be deployed in four bomber commands (the XX BC of 4 groups in India-China, the XXI BC of 16 groups in the Marianas, the XXII BC of 24 groups in the Philippines and Okinawa, and the XXIII BC of 4 groups in the Aleutians).
Original plans for XX Bomber Command to employ two combat wings in China (the 58th and 73rd Combat Bomb Wings) were changed on 2 March 1944 when limited numbers of operational B-29s resulted in only the 58th CBW assigned. There, after poor bombing results, and as developing operations deemed the original complex organization unnecessary, it was deemed a redundant level of command and its four groups moved to Guam in April 1945 as part of XXI Bomber Command.
The bases in China were part of the China Burma India Theater of World War II for administrative purposes.  The commander of the XX Bomber Command had no control over stations, bases, units, and personnel not directly assigned to him, and none over shipping and other logistic support essential to the operation.  However the Commander-in-Chief of the XX Bomber Command reported directly to the JCS in Washington and was not under SEAC operational control like the rest of the personnel in the CBI.
The British planning to deploy their new Very Long Range Bomber Force (of about 22 squadrons) to the Far East for final operations against the Japanese, proposed that Twentieth Air Force be controlled by the Combined Chiefs, as had the air forces in Europe, but when the Americans rejected the proposal (because the forces involved were overwhelmingly American), the British dropped the issue.