The Marianas chain of islands, consisting primarily of Saipan, Tinian, and Guam, were considered as being ideal bases from which to launch B-29 operations against Japan. The islands were about 1500 miles from Tokyo, a range which the B-29s could just about manage. Most important of all, they could be put on a direct supply line from the United States by ship.
However, in 1943, the Marianas were firmly under Japanese control. Plans for the conquest of the Marianas had been put forward as early as May 1943 by Admiral Ernest King at the Anglo-American Trident Conference in Washington, but not much was done at the time since the US Navy was locked in a bitter contest further south in the Solomons and New Guinea. It was not until September of 1943 that the full potential of the Marianas as a B-29 base to attack Japan was realized. On October 4, 1943, General Henry H. Arnold approached the Joint Planning Staff with a proposal for the seizure of the Marianas at the earliest possible date as bases for the B-29. Much of the combat that followed in the Pacific for the next two years had as its major objective the seizure of B-29 bases ever closer and closer to Japan.
The plan was formally approved at the Cairo Conference between President Franklin Roosevelt, Chinese President Chiang Kai-shek, and British Prime Minister Winston Churchill, held in November of 1943. Admiral Chester Nimitz was to assume overall command of the effort.
First to be attacked was Saipan. On June 11, 1944 a four-day naval and air bombardment of the island began. On the 15th, Marine units stormed ashore, followed a day later by Army units. After several weeks of heavy fighting, during which over 3000 American and 24,000 Japanese lives were lost, the island was finally declared secure on July 9. The seizure of Saipan enabled invasions of Guam and Tinian to proceed, which were attacked on July 20 and July 23 respectively. These islands were declared secure on August 9. The US now had its bases.
Construction of the B-29 airfields on Saipan began almost immediately, even while the fighting was still going on. Initial construction took place at a former Japanese airstrip called Aslito. This was later renamed Isley Field, after Navy Commander Robert H. Isely (unfortunately his name was misspelled and the incorrect version stuck).
The XXI Bombardment Command had been assigned the overall responsibility of the B-29 operations out of the Marianas bases. The XXI BC had been activated at Smokey Hill on March 1, 1944. In August, Major General Haywood S. Hansell Jr was directed to take over command of the XXI BC. The field on Saipan was to be occupied by the 73rd Bombardment Wing (which consisted of the 497th, 498th, 499th, and 500th Bombardment Groups). The 73rd BW has been formed at Salina, Kansas on November 28, 1943 with Col. Thomas H. Chapman as the first commander. In March, Col. Chapman was replaced by Brigadier General Emmett O'Donnell.
The 73rw BW was ordered to the Marianas rather than to the CBI. The first B-29 arrived on Saipan on October 12, 1944. It was piloted by General Hansell himself. By November 22, over 100 B-29s were on Saipan. The XXI BC was assigned the task of destroying the aircraft industry of Japan in a series of high-altitude, daylight precision attacks. However, General Hansell was fully aware that his crews still lacked the necessary experience to carry out such missions. In late October and early November 1944, a series of tactical raids were carried out as training exercises for the crews. On October 27, 18 B-29s attacked Japanese installations on Truk. Four Superfortresses had to abort because of the usual engine problems, and combat formations were scrappy. Truk was hit again by B-29s on October 30 and November 2.
Aware that there was now a new threat, Japanese aircraft based on Iwo Jima staged a low-level raid on Isley Field on November 2, damaging several B-29s on the ground. Retaliatory strikes were ordered on Iwo Jima on November 5 and 11, but the results were again poor. As in the Matterhorn campaign, the B-29s were in danger of being dissipated in tactical missions and even these were not all that successful.
General Arnold was pressing Hansell for an attack on Japan as soon as possible. The first raid against Japan took place on November 24, 1944. The target was the Nakajima Aircraft Company's Musashi engine plant just outside Tokyo. It was the first attack on Tokyo since the Doolittle raid of over two years earlier. 111 B-29s took off, led by Brigadier General Emmett O'Donnell flying in Dauntless Dotty. Seventeen of them had to abort due to the usual spate of engine failures. The remainder approached the target at altitudes of 27-32,000 feet. For the first time, the B-29 encountered the jet stream, which was a high-speed wind coming out of the west at speeds as high as 200 mph at precisely the altitudes at which the bombers were operating. This caused the bomber formations to be disrupted and made accurate bombing impossible. In addition, the Nakajima plant was covered in patchy cloud at the time and only 24 of the B-29s dropped their bombs in even roughly the right place. The target was hardly damaged, and one B-29 was rammed by a Japanese fighter and destroyed. It was not a good start.
The Musashi plant was revisited ten more times over the next few weeks. The results were still disappointing. Only ten percent of the damage done by the bombs was actually inside the plant area. 40 bombers had been lost in these eleven raids, many to accidents caused by engine failures.
In December there were a series of raids against the Mitsubishi engine plant at Nagoya. Although some 17 percent of the facility was gutted, Japanese defenses were becoming more effective and losses to enemy action were now reaching four or five per mission.
The Marianas operation was going the way of Operation Matterhorn, with losses being high and not much damage to the enemy being done. Since little progress was being made, General Arnold recalled General Hansell and moved General LeMay from India to take over the XXI BC. LeMay arrived in the Marianas on January 20, 1945.
Before he left, General Hansell had introduced some reforms which were to have lasting effects. Engine failures were still a problem for the B-29 as late as mid-January of 1945, and the abort rate was running at 23 percent per mission. In order to reduce the abort rate, Hansell ordered a weight reduction program for the B-29 in which one of the fuel tanks was taken out and some of the 0.50-inch machine gun ammunition was removed, shaving over 6000 pounds from the weight of each plane. Maintenance was centralized under Hansell's headquarters rather than having it being split up between the various Bombardment Groups. As a result of these changes, B-29 endurance began to lengthen, engine life was extended from 200 to 750 hours, and the abort rate began to decline. By July of 1945, it was down to less then seven percent per operation.
In January of 1945, the 313th Bombardment Wing (6th, 9th, 504th, and 505th Bombardment Groups) under the command of Brig Gen John H. Davies took over the newly-built North Field on Tinian. They took part in a high-altitude daylight raid on Kobe on February 4.
This was the last of the raids on Japan for a while, General LeMay's B-29s being diverted to the campaign to capture Iwo Jima. Iwo Jima was considered vital to the B-29 campaign, since it could be used to base fighters capable of escorting the B-29s to Japan, as well as an emergency field midway between the Marianas and their targets.
Concerned about the relative failure of the B-29 offensive to deal any crippling blows to Japan, General LeMay issued a new directive on February 19. General LeMay had analyzed the structure of the Japanese economy, which depended heavily on cottage industries housed in cities close to major industrial areas. By destroying these feeder industries, the flow of vital components to the central plants could be slowed, disorganizing production of weapons vital to Japan. He decided to do this by using incendiary bombs rather than purely high-explosive bombs, which would, it was hoped, cause general conflagrations in large cities like Tokyo or Nagoya, spreading to some of the priority targets.
In addition, LeMay had concluded that the effects of the jet stream, cloud cover, and high operating altitudes were to blame for the failure of the B-29 raids to do any significant damage to the Japanese war industry. The initial raids against Japan had taken place at high altitudes in order to stay above anti-aircraft fire and the effective altitude of defending fighters. LeMay suggested that high-altitude, daylight attacks be phased out and replaced by low-altitude, high-intensity incendiary raids at nighttime. The aircraft would attack individually, which meant that no assembly over the base at the start of the mission or along the way would be needed. Consequently, aircraft could go directly from the base to the target and return, maximizing the bomb load and saving substantially on fuel. He ordered that all the B-29s be stripped of their General Electric defensive gun systems, leaving only the tail gun. The weight of extra crew members, armament, and ammunition would bo into bombs, each B-29 being loaded down with six to eight tons of M69 incendiary bombs. These bombs would be dropped from altitudes of only 5 to 6 thousand feet. This strategy would enable the B-29s to escape the effects of the jet stream and would get the bombers below most of the cloud cover. In addition, the B-29s would no longer have to struggle up to 30,000 feet and this would save on fuel and on wear and tear to the engines. It was believed that Japanese night fighter forces were relatively weak, but flak losses were expected to be substantial.
The first raid to use these new techniques was on the night of March 9-10 against Tokyo. Another wing--the 314th Bombardment Wing (19th, 29th, 39th, and 330th BG) commanded by Brig. Gen. Thomas S. Power--had arrived in the Marianas and was stationed at North Field on Guam. A total of 302 B-29s participated in the raid, with 279 arriving over the target. The raid was led by special pathfinder crews who marked central aiming points. It lasted for two hours. The raid was a success beyond General LeMay's wildest expectations. The individual fires caused by the bombs joined to create a general conflagration known as a firestorm. When it was over, sixteen square miles of the center of Tokyo had gone up in flames and nearly 84,000 people had been killed. Fourteen B-29s were lost. The B-29 was finally beginning to have an effect.
On the night of March 11-12, the B-29s were in action again, this time against the city of Nagoya. This time, the scattered fires did not join to create a general firestorm, and only two square miles of the city were destroyed. On the night of March 13-14, eight square miles of Osaka went up in flames. On March 16-17, three square miles of Kobe were destroyed, and on March 19-20 in a return visit to Nagoya, three more square miles were destroyed. This destructive week had killed over 120,000 Japanese civilians at the cost of only 20 B-29s lost. The strategic bombing campaign had at last been justified.
By March 20, XXI Bombardment Corps had run out of incendiaries, forcing a momentary pause. While waiting for new incendiary stocks, LeMay devoted his B-29s to flying tactical missions over the island of Kyushu in support of the invasion of Okinawa. Airfields and support facilities were primary targets. These raids lasted until early May.
In April of 1945, General LeMay gave new orders for more incendiary raids. This time, aircraft engine factories at Musashi and Nagoya were to be hit, but urban areas in Tokyo, Nagoya, Osaka, Kawasaki, Kobe, and Yokohama were also to be attacked. On April 7, 153 B-29s struck the aircraft-engine complex at Nagoya, destroying about 90 percent of that facility. Five days later, 93 B-29s destroyed the Nakajima factory at Musashi. The Japanese aircraft engine industry essentially ceased to exist after this time.
On April 13, 327 B-29s burned out eleven more square miles of Tokyo. Seven more B-29s were lost.
In mid-April, the XXI BC received the 58th Bombardment Wing, which had been redeployed from the now-defunct XX BC in the CBI theatre to West Field on Tinian.
On May 14, 472 B-29s attacked the area in and around the Mitsubishi engine factory at Nagoya. Two nights later, another visit to Nagoya devastated another four square miles of that city. On May 23 and May 25, Tokyo was hit again. Although these two Tokyo raids had cost 43 B-29s, over 50 percent of the city had now been destroyed.
Alarmed at the increasing B-29 losses, a change of tactics was ordered. In an attempt to confuse the enemy defenses and to lure Japanese fighters into an air battle in which many of them would be destroyed, high-altitude daylight attacks were temporarily resumed. On May 29, 454 B-29s appeared over Yokohama, but this time they were escorted by P-51 Mustangs from Iwo Jima. In the resulting dogfight, 26 Japanese fighters were destroyed as against the lost of four B-29s and three P-51s. Thereafter, the Japanese hoarded their surviving fighters for a last-ditch effort against the inevitable invasion force, and the air defense of cities became a lesser priority. By June of 1945, Japanese interceptors were seen much less frequently and the B-29s had virtually free reign over all Japanese airspace.
On June 5, the B-29s attacked Kobe with such effectiveness that the city was crossed off the target list as not worth revisiting. By the end of the month, the six major cities on LeMay's list had all been effectively destroyed.
The newly-arrived 315th Bombardment Wing (16th, 331st, 510st, and 502nd BGs) stationed at Northwest Field on Guam was equipped entirely with the B-29B variant. This variant had been built by Bell Aircraft at Marietta, Georgia and had been manufactured without the General Electric gun system in order to save weight. The 315th had been trained for low-altitude, nighttime pathfinder missions. Between June 26 and August 10, they carried out a series of strikes against oil production facilities which essentially shut down the Japanese oil industry.
In late March of 1945, the 313th Bombardment Wing began a series of mining operations against Japanese ports. Nearly 13,000 acoustic and magnetic mines were placed in the western approaches to the narrow Shimonoseki strait and the Inland Sea as well as in the harbors of Hiroshima, Kure, Tokyo, Nagoya, Tokuyama, Aki, and Noda. The mining operation was extremely successful and brought Japanese coastal shipping to a standstill by April. In May, merchant vessels were ordered to break through the line of mines, and 85 of them were sunk. These mining efforts were so effective that the postwar Strategic Bombing Survey credited the B-29 with 9.3 percent of the total Japanese shipping losses during the war.
By mid-June, most of the larger Japanese cities had been gutted, and LeMay ordered new incendiary raids against 58 smaller Japanese cities. By now, the B-29 raids were essentially unopposed by Japanese fighters. In late June, B-29 crews felt sufficiently confident that they began to drop leaflets warning the population of forthcoming attacks, followed three days later by a raid in which the specified urban area was devastated.
In June of 1945, the XX and XXI Bombardment Commands were grouped under the US Strategic Air Forces, Pacific, under the command of General Carl A. Spaatz.
By the end of June, the civilian population began to show signs of panic, and the Imperial Cabinet first began to consider negotiating an end to the war. However, at that time, the Japanese military was adamant about continuing on to the bitter end.
During the Marianas operation, a total of 25,500 individual aircraft sorties were flow, and 170,000 tons of conventional ordnance had been dropped. A total of 371 bombers had been lost.
Order of Battle, 20th Air Force, 1944-45:
XXI Bombardment Command
25th, 44th, 45th, 395th Bombardment Squadrons.
395th deactivated Sept-Oct 1944.
676th, 677th, 678th, 679th Bombardment Squadrons.
679th deactivated Sept-Oct 1944.
768th, 769th, 770th, 771st Bombardment Squadrons.
771st deactivated Sept-Oct 1944.
792nd, 793rd, 794th, 795th Bombardment Squadrons. 759th deactivated Sept-Oct 1944.
869th, 870th, 871st Bombardment Squadrons
873rd, 874th, 875th Bombardment Squadrons
877th, 878th, 879th Bombardment Squadrons
881st, 882nd, 873rd Bombardment Squadrons
24th, 39th, 40th Bombardment Squadrons.
1st, 5th, 99th Bombardment Squadrons.
398th, 421st, 680th Bombardment Squadrons.
680th did not join until June of 1945.
482nd, 483rd, 484th Bombardment Squadrons.
28th, 30th, 93rd Bombardment Squadrons.
6th, 43rd, 52nd Bombardment Squadrons.
60th, 61st, 62nd Bombardment Squadrons.
457th, 458th, 459th Bombardment Squadrons.
15th, 16th, 17th Bombardment Squadrons.
355th, 356th, 357th Bombardment Squadrons.
21st, 41st, 485th Bombardment Squadrons.
402nd, 411st, 430th Bombardment Squadrons.