Japanese air attacks on the Mariana Islands

During World War II, a series of Japanese air attacks on the Mariana Islands took place between November 1944 and January 1945. These raids targeted United States Army Air Forces (USAAF) bases and sought to disrupt the bombing of Japan by Boeing B-29 Superfortress heavy bombers operating from the islands. The Japanese lost 37 aircraft during this operation, but destroyed 11 B-29s and damaged a further 43. Preparations were also made for commando raids on the bases in early and mid-1945 but these did not go ahead.

While the attacks on the Mariana Islands did not seriously disrupt the USAAF air campaign, they had an effect on other American operations. After determining that the Japanese raiders were staging through Iwo Jima, American forces stepped up their attacks on that island. While the decision to invade Iwo Jima had been made before the raids commenced, stopping the attacks formed part of the justification for the landing. In addition, further air defense units were deployed to the Mariana Islands to protect the B-29 bases.

Background

United States forces recaptured Guam and captured Saipan and Tinian in the Mariana Islands between June and August 1944, as part of the Mariana and Palau Islands campaign.Tillman (2010), p. 68 These islands were needed to provide bases for USAAF Twentieth Air Force B-29 Superfortress heavy bombers to attack the Japanese home islands.Cate and Olson (1953), p. 578 Construction of the large air bases needed to support B-29s began on Saipan in June 1944, before the end of the Battle of Saipan, and work on air fields on Tinian and Guam commenced in July and August respectively.Tillman (2010), pp. 70–73 The B-29s of the XXI Bomber Command began to arrive at Saipan starting on October 12, and the 73rd Bombardment Wing began flying warm-up missions against Japanese-held islands in the Pacific on October 27 in preparation for operations against Japan itself.Tillman (2010), pp. 77–79

The USAAF bases in the Mariana Islands were within range of a number of Japanese air bases in the Pacific. These included Wake Island to the east, Truk and the Gilbert and Marshall Islands to the southeast, Woleai to the south and Yap to the southwest. To the north the Japanese had air bases in the Nampo Shoto chain of islands and Bonin Islands, which included three airstrips on Iwo Jima. Several of the minor islands in the Mariana chain also remained in Japanese hands, and there were airfields on Rota and Pagan.Cate and Olson (1953), pp. 578–579 The Japanese were unable to use most of these bases, however, as they had been isolated and heavily damaged by United States air attacks, and the Imperial Japanese Army Air Force (IJAAF) and Imperial Japanese Navy (IJN) had relatively few aircraft and pilots available.Cate and Olson (1953), p. 579

Despite the limited threat of attack, the United States military took steps to protect the B-29 bases in the Mariana Islands. The USAAF's Seventh Air Force played the most important role, and continuously attacked the Japanese-held islands until just before the end of the war. United States Navy (USN) and United States Marine Corps (USMC) aircraft and XXI Bomber Command B-29s also occasionally participated in these attacks. The Seventh Air Force also provided air defence for the Mariana Islands; this task was assigned to the 318th Fighter Group, which was equipped with Republic P-47 Thunderbolt fighters, and the 6th Night Fighter Squadron which flew Northrop P-61 Black Widows. The Thunderbolts were also responsible for suppressing the Japanese-held Mariana Islands, though it proved difficult to stop the 3,600-man garrison from repairing the airfield on Pagan.Cate and Olson (1953), pp. 580–581 In addition, the US Army stationed elements of eight anti-aircraft gun battalions and two searchlight battalions on Saipan between July 1944 and February 1945.Stanton (1984), pp. 490–509 The head of the USAAF General "Hap" Arnold, who also directly commanded the Twentieth Air Force, was concerned about whether these defenses were sufficient, particularly given the high cost of the Superfortress bombers. Accordingly, he allocated a Microwave Early Warning (MEW) radar to protect the bases on Saipan. This advanced radar was not immediately installed, however, as the local commanders believed that the island's air defenses were adequate.

Japanese attacks

The first Japanese air attacks on the B-29 bases occurred while they were under construction. Small numbers of Japanese aircraft flying from Guam, Peleliu, Iwo Jima and Truk made occasional raids on the American forces on Saipan during the fighting there, but caused little damage.Denfeld (1997), p. 59 Between June 24 and July 21 the 6th Night Fighter Squadron intercepted 37 raids on Saipan, and claimed three "kills". These raids typically comprised twelve IJN Mitsubishi G4M bombers (codenamed "Betty" by the Allies),McFarland (1998), pp. 38–39 or IJAAF Mitsubishi Ki-67 ("Peggy") bombers operating from bases on mainland Japan and staging through Iwo Jima.Francillon (1970), p. 190.Bueschel (1997), pp. 5–6. The attacks disrupted airbase construction on several days and contributed to delays completing the B-29 base on Saipan, Isley Field.Fagg (1983), p. 305 Small numbers of Japanese soldiers who had avoided capture at the end of the battles on the islands also raided the B-29 bases on occasion, mainly in search of food.Werrell (1996), p. 127

The main Japanese air offensive against the Mariana Islands began in early November 1944. On November 1, a B-29 flying from the Marianas overflew the Tokyo region for the first time. The next day, nine or ten IJN G4Ms belonging to the IJN Attack Hikōtai 703 struck Isley Field and the adjacent Kobler Field on Saipan. The raiders arrived over Saipan shortly after 1:30 am and dropped their bombs from low altitude. Only five bombs struck Isley Field, and these caused little damage. A Black Widow from the 6th Night Fighter Squadron shot down one of the G4Ms and another two were lost to other causes.Cate and Olson (1953), p. 581Sakaida and Takaki (2001), p. 27 On November 3 the Imperial General Headquarters issued a statement which falsely claimed that Japanese aircraft had bombed and destroyed fifteen locations in Saipan and Tinian.Hoyt (1987), p. 376 A further attack by either five or ten G4Ms with fighter escorts took place at 1:30 am on November 7, but also caused little damage. The USAAF official history states that three G4Ms were downed in this raid while another source states there were no Japanese losses.Sakaida and Takaki (2001), p. 28 Imperial General Headquarters claimed that 20 B-29s out of 40 located were destroyed in the November 7 raid.Hoyt (1987), p. 377 These and all subsequent Japanese air attacks on the Marianas were overseen by the Air Training Army.Foreign Histories Division, Headquarters, United States Army Japan (1980), pp. 28–29

Further attacks were conducted against Saipan during late November in an attempt to disrupt the American offensive.Bradley (1999), p. 10 On November 24, Marianas-based B-29s conducted their first raid against Japan, bombing targets in and around Tokyo.Tillman (2010), pp. 84–86 Three days later the Japanese mounted two raids against their bases. During the early hours of November 27, two G4Ms flying from Iwo Jima struck Isley Field from low altitude and escaped after destroying one B-29 and damaging eleven others.Tillman (2010), p. 86 This attack came as a surprise to the Americans, and construction lights were still on at Isley at the start of the raid.Cate and Olson (1953), p. 582

Later that day, twelve bomb-equipped Mitsubishi A6M "Zero" fighters from the IJN's 252 Kōkūtai (252 Air Group) accompanied by two Nakajima C6N "Myrt" reconnaissance aircraft for navigation purposes departed Iwo Jima for Saipan. The attackers flew just above sea level to avoid US radar, and one of the A6Ms was forced to divert to Pagan after its propeller struck a wave; this aircraft was shot down by a USAAF Thunderbolt while attempting to land. The remaining eleven A6Ms arrived over Saipan at noon, shortly after XXI Bomber Command's second raid on Tokyo had departed. These aircraft strafed Isley Field destroying three or four B-29s and damaging up to two others. One of the Japanese pilots landed his fighter on Isley Field and fired on airfield personnel with his pistol until he was killed by rifle fire; this incident was witnessed by Brigadier General Haywood S. Hansell, the commander of XXI Bomber Command.Sakaida and Takaki (2001), p. 33Hata, p. 117. The leader of the raid was Lieutenant Junior Grade Kenji Ōmura. The raid was conceived and planned as a one-way mission. The 252 Air Group was based at Tateyama Air Field and forward deployed to Iwo Jima. None of the ten other A6Ms survived; four were shot down by USAAF fighters and six by anti-aircraft guns. The U.S. gunners also downed a USAAF Thunderbolt in circumstances which an official assessment later described as "inexcusable". On the night of November 28/29 six or eight G4Ms from Attack Hikōtai 704 bombed Isley Field from high altitude but caused little damage.Tagaya (2001), p. 91

The United States military took steps to improve Saipan's defenses after the raids of November 27. Two USN destroyers were stationed northwest of the island to provide radar warning of further attacks. These ships detected some of the later Japanese raiders, but others managed to arrive undetected. An AN/TPS-3 radar was also flown to Saipan from Hawaii. Arnold became frustrated that the MEW still was not in use, and on December 3 Fleet Admiral Chester W. Nimitz, the commander of the Pacific Ocean Areas, ordered that the highest priority be given to installing the radar. Despite this, it still was not ready until after the conclusion of the Japanese air campaign.Cate and Olson (1953), pp. 582–583 Two Consolidated B-24 Liberator bombers fitted with air-to-air radar sets were also dispatched to Saipan. This was the first use of airborne warning and control aircraft by the United States, but they were not used in combat.McFarland (1998), p. 39

Further attacks were mounted in December. On December 7, Japanese aircraft, which included Attack Hikōtai 704 G4Ms and 110th Sentai (Wing) Ki-67s, conducted a simultaneous attack from high and low altitudes which destroyed three B-29s and damaged another 23.Bueschel (1997), p. 7. Japanese losses were heavy, however, with six out of eight Ki-67s of the 110th Sentai lost during this attack, the first carried out by this unit. The largest attack on Saipan occurred on the night of December 25/26 when 25 Japanese aircraft again attacked from high and low altitudes and destroyed one B-29, damaged three beyond repair and caused minor damage to a further eleven.Cate and Olson (1953), pp. 581–582 Also on 26 December, the Air Training Army was redesignated the 6th Air Army but retained the mission of conducting attacks on the Marianas.Foreign Histories Division, Headquarters, United States Army Japan (1980), p. 26

The raid on Christmas night was the last major Japanese attack on the Marianas. On January 2, a single Japanese aircraft destroyed one B-29 and damaged another three. A further two small raids were attempted in January and one on February 2, but none of five aircraft dispatched reached the islands and four were shot down.Werrell (1996), p. 128 In early February the 6th Air Army's parent headquarters, the General Defense Command (GDC), reached the conclusion that the raiding forces being dispatched against the American bomber bases were too small to be effective. As it was not possible to allocate additional aircraft to bolster these missions, the GDC directed that the offensive cease and that the 6th Air Army be held in reserve to be used against any Allied forces which landed in the Japanese home islands.Foreign Histories Division, Headquarters, United States Army Japan (1980), p. 27