The Last IJN Carrier Aircraft

IJN Taihō was designed to carry 53 aircraft (24 A7M, 18 D4Y, 6 C6N plus 5 spares). Only D4Y were ready when she fought in Philippine Sea. Since her overall dimensions were approximately the same as the Shokakus but her hangar smaller she carried a small contingent on her flight deck so the distribution among the three ships was essentially equal.

The IJN Shinano’s organic air group was intended to consist of 18 Mitsubishi A7M Reppū (Allied reporting name “Sam”) fighters (plus two in storage), 18 Aichi B7A Ryusei (“Grace”) torpedo-dive bombers (plus two in storage), and 6 Nakajima C6N Saiun (“Myrt”) reconnaissance aircraft (plus one in storage). The remainder of the hangar space would have held up to 120 replacement aircraft for other carriers and land bases

Mitsubishi A7M Reppu

The Mitsubishi A7M Reppu was supposed to be the replacement for the struggling A6M, but never got past a prototype/test programme. It showed promise but also had many faults and could in no way be considered an active type. Large production orders were supposedly placed off the drawing board, but by this stage the Japanese had no operational carriers, so even if the war had dragged on for another couple of years, none would have ever put to sea. The Reppu never entered service mainly because of the constant change in specifications it was submitted to by the IJNAF Headquarters.

On May 6, 1945 The Mitsubishi A7M1, Navy Experimental 17-Shi Ko (A) Type Carrier Fighter Reppu (Hurricane) makes its first flight. The aircraft had been under development since 1942 as a replacement for the Mitsubishi A6M, Navy Type 0 Carrier Fighter, Allied Code Name “Zeke.” The A7M1 was as maneuverable as the “Zeke” but was underpowered and lacked performance. Only ten of these aircraft, given the Allied Code Name “Sam,” were built by Mitsubishi at Nagoya.

A7M3-J and A7M3 Model 23: The former was to have a turbocharged MK9A engine with a estimated speed of 403mph at 32,810ft., this height being reached in 15min.; drawings completed in Nov. of 1944 and in Feb. of 1945, the mock-up was inspected by the Navy; prototype was to be complete by October of 1945 but the close of the war prevented this. The latter was based on the A7M2 fuselage and had a MK9C powerplant; had no folding wings and the pilot was provided with armored windscreens and aft fuel tankage; armed with six Type 99 20mm cannon; max speed of 399mph at 28,454mph; prototype scheduled for completion in December of 1945 and thus was still under construction by war’s end.

Navy Carrier Attack Bomber Tenzan “Heavenly Mountain” Model 11 – Nakajima B6N2

In 1939 the Imperial Japanese Navy drew up its specification for a carrier-based torpedo-bomber to supersede the Nakajima B5N. The specifications issued by the navy called for very modern characteristics. A maximum speed of 288 mph (463 km/h), a cruising speed of 230 mph (370 km/h) and a range of 1,000 nautical miles (3335 km) without a bombload. To meet the requirement, Nakajima decided to use an airframe very similar to that of the earlier aircraft, differing primarily in its vertical tail surfaces. The navy had specified use of the Mitsubishi Kasei radial engine, but Nakajima decided to use instead its own 1,870 hp (1395 kW) Nakajima NK7A Mamoru 11 radial engine of similar output driving a four bladed Hamilton type propeller. The first of two prototypes was flown in spring 1941, but initial flight testing revealed a number of problems, including engine vibration and overheating, but the most serious was that of directional stability, requiring revised vertical tail surfaces. Final flight testing carried out aboard the aircraft carriers Ryuho and Zuikaku in the end of 1942, revealed further problems with the tuning of the engine and the need to reinforce the arrester hook and landing gear. It was not until February 1943 that the type entered production as the Navy Carrier Attack Bomber Tenzan Model 11, company designation Nakajima B6N1, incorporating a number of refinements as a result of extended flight testing. However, after only 135 production Tenzan (heavenly mountain) aircraft had been delivered a new crisis arose when Nakajima was ordered to terminate manufacture of the Mamoru engine, and use the more reliable 1,850 hp (1380 kW) Mitsubishi MK4T Kasei 25 engine, a step also taken to allow greater emphasis to be placed on production of the widely-used Nakajima Homare and Sakae engines.

The company was now compelled to use the engine which the navy had specified originally, the Mitsubishi Kasei, but fortunately the adaptation of the B6N airframe to accept this powerplant presented no major difficulties. The resulting aircraft, which was also the major production version, had the designation B6N2 and differed only from the B6N1 by the installation of the Mitsubishi Kasei 25 engine. The B6N2a variant had the rear-firing 7.7 mm (0.303 in) machine-gun replaced by one of 13 mm (0.51 in) calibre. When production ended, Nakajima had built a total of 1,268 B6Ns of all versions, this number including two modified B6N2 airframes which had served as prototypes for a proposed land-based B6N3 Model 13. The powerplant had been the improved 1,850 hp (1380 kW) Mitsubishi MK4T-C 25C version of the Kasei engine and the strengthened landing gear had larger wheels for operation from unprepared runways, but production did not start before the war ended. Allocated the Allied codename ‘Jill’, the B6Ns saw intensive use during the last two years of the war for conventional carrier operations and, in the latter stages, in kamikaze roles.


Nakajima B6N2 – Nakajima was ordered to cease using the Mamoru engine and use instead the Mitsubishi Kasei 25 engine, thus resulting in the redesignated B6N2. Although the Kasei 25 was slightly less powerful, this was offset by introducing a less drag version of the exhaust ports which also gave a slight jet-thrust like boost effect.

Nakajima B6N2a – This type differed from the B6N2 only by having a rear firing machine gun of 13 mm (0.51 in) calibre, instead of the 7.7 mm (0.303 in) type used on the B6N2.

Nakajima B6N3 – Two conversions of the B6N2a resulted in the B6N3 prototypes equipped with 1,850 hp (1380 kW) Mitsubishi MK4T-C Kasei 25C engines for evaluation as land-based bombers.

Nakajima C6N Saiun reconnaissance aircraft

The three-seat Nakajima C6N Saiun, of which 463 were produced, was one of the few World War II reconnaissance aircraft specifically designed for operating from carriers. With a maximum speed of 379 mph, a maximum range of 3,300 miles, and service ceiling of 34,236 ft, the C6N proved virtually immune from Allied interception. Unfortunately for Japan, it did not become available for service until the Mariana Islands Campaign in the summer of 1944.

Identifying the need for a long-range carrier-based reconnaissance aircraft, as a result of early experience in the Pacific war, the Imperial Japanese Navy drew up a specification which it issued to Nakajima in early 1942 for an aircraft to meet this requirement. The combination of high-speed, long-range and carrier compatibility presented considerable problems which Nakajima resolved by adopting its own efficient 1,820-hp (1358-kW) NK9B Homare 11 engine and incorporating in the wing design leading-edge slats and a combination of Fowler-type and split trailing-edge flaps. Appearing similar in external configuration to the company’s B6N, the Nakajima C6N had a fuselage also accommodating a crew of three, but the lower surfaces and sides of the structure incorporated camera ports and observation windows.

The first C6N1 prototype made its maiden flight on 15 May 1943, but disappointing performance of the Homare 11 engine led to 18 more prototypes/preproduction aircraft, some tested with the more powerful Homare 21, before the type was ordered into production in early 1944 as the Navy Carrier Reconnaissance Plane Saiun (painted cloud) which had the company designation Nakajima C6N1. Entering service in the summer of 1944, these aircraft soon demonstrated their long-range capability in keeping a watchful eye on the US fleet, and their speed was good enough to give them almost complete immunity from interception by Allied fighters. The type played a significant role in the closing stages of the war and a total of 463 had been built by Nakajima when production ended in August 1945. Originally designed for high-speed reconnaissance, Nakajima’s C6N, known to the Allies as “Myrt,” proved especially capable despite the absence of onboard radar. A small number of C6N1-S two-seat night fighter conversions from C6N1s, armed with two 20- mm cannon mounted to fire obliquely forward and upward. At least six C6N1s were converted with obliquely angled 20mm or 30mm cannons as the C6N1-S. One C6N2 which was flown with a prototype installation of a 1,980-hp (1476-kW) Homare 24 turbocharged engine. Projected, but not built, were the C6N1-B carrier-based attack bomber and the C6 3 night-fighter powered by the Homare 24 engine.

This outstandingly clean aircraft was an example of Japanese specialization defeated by circumstances. No other nation built a purpose-designed carrier-based reconnaissance aircraft in World War II. and the 17-Shi (spring 1942) specification was very challenging. The C6N was faintly like a Fw 190 stretched to seat a pilot, navigator/observer and radio operator/gunner in tandem As evidence of advanced design, the flaps were tabbed Fowlers, and the laminar-section wing (only slightly larger than a Zero’s) also had drooping ailerons and slats, and was almost entirely given over to six integral tanks. The troublesome Homare was beautifully cowled and had thrust-giving ejector exhausts. Another feature that was new to Japan was thick-skinned structure, reducing the numbers of parts and cutting the number of rivets from 220.000 for a Zero to under 100.000. Altogether 463 of these speedy machines were built, but need for the C6N1-B was swept away by loss of the carrier force.

Yokosuka D4Y Suisei dive-bomber

The Yokosuka D4Y (“Judy”) reconnaissance/dive-bomber entered service on Japanese carriers early in 1943 and was very fast for a bomber. Initially assigned to reconnaissance units, it was intended to replace the D3A, but it was insufficiently armed and protected and suffered from structural weakness in dives. In common with most other Japanese aircraft, it was used for kamikaze attacks, and a D4Y carried out the last kamikaze attack of the war on 15 August 1945. A total of 2,819 D4Ys were built.

Well-proportioned and purposeful in appearance, the Yokosuka D4Y possessed an excellent performance and owed much of its concept to the German He 118, for whose manufacturing rights Japan negotiated in 1938. Designed as a fast carrier-based attack bomber and powered by an imported Daimler-Benz DB 600G engine, the D4Y1 was first flown in December 1941; D4Y1-C reconnaissance aircraft were ordered into production at Aichi’s Nagoya plant, the first of 660 aircraft being completed in the late spring of 1942. The first service aircraft were lost when the Soryu was sunk at Midway. Named Suisei (comet) in service and codenamed ‘Judy’ by the Allies, many D4Yls were completed as dive-bombers, and 174 Suiseis of the 1st, 2nd and 3rd Koku Sentais were embarked in nine carriers before the Battle of the Philippine Sea. However, they were intercepted by American carriers, and suffered heavy casualties without achieving any success. A new version with 1044-kW (1,400-hp) Aichi Atsuta 32 engine appeared in 1944 as the D4Y2 but, in the interests of preserving high performance, nothing was done to introduce armour protection for crew or fuel tanks, and the sole improvement in gun armament was the inclusion of a 13.2-mm (0.52-in) trainable gun (replacing the previous 7.92-mm/0.31-m gun) in the rear cockpit. This version suffered heavily in the battle for the Philippines. Problems of reliability with the Atsuta (DB 601) engine led to adoption of a Kinsei 62 radial in the D4Y3, and this engine was retained in the D4Y4 which was developed in 1945 as a single-seat suicide dive-bomber. A total of 2,038 production D4Ys was completed.


These early versions of the D4Y were difficult to keep in service because the Atsuta engines were unreliable and difficult to maintain in front line service. From the beginning some had argued that the D4Y should be powered by an air-cooled radial engine, a type Japanese engineers had experience with and trusted. The aircraft was therefore fitted with the reliable Mitsubishi MK8P Kinsei 62, a fourteen-cylinder two-row radial engine. This version was the Yokosuka D4Y3 Model 33.

Flight trials showed that performance was roughly the same as the D4Y2, the gain being easier maintenance and greater reliability. Although the new engine improved ceiling and rate of climb (over 10,000 m, and climb to 3,000 m in 4.5 minutes, instead of 9,400 m and 5 minutes), the higher fuel consumption resulted in shorter range and a slower cruise speed, while the bulky engine obstructed the forward and downward view of the pilot, hampering carrier operations. These problems were tolerated because of the increased availability of the new variant. Late production aircraft also received provisions for RATO units (Rocket Assisted Take Off) to improve take-off from smaller aircraft carriers.

B7A2 Unit: Kougeki (Attack) 5th Hikotai, 752nd Kokutai Serial: 752-03 Katori Naval Air Base, Chiba prefecture, end of April 1945.

Aichi’s B7A Ryusei torpedo bomber

Aichi’s B7A Ryusei torpedo bomber (‘Grace’) was part of the 16-Shi (1942) programme. It was intended to extend the reach of Japanese carriers and thus to minimise the problem of carrier air defence: if the Japanese fleet could outreach the US fleet, and if its aircraft could penetrate US defences, then it could strike without being struck. The Japanese consistently managed to outrange the US fleet, but the combination of effective fighter control and effective anti-aircraft fire made that outreach useless. The Ryusei was intended to replace both the standard attack aircraft: the B6N torpedo bomber and the D4Y dive bomber. Given enough engine power, an airframe stressed to dive-bomb could lift a torpedo. That was the case with both the US SB2C Helldiver (although it was not used as a torpedo bomber) and the British Barracuda (a torpedo bomber used exclusively as a dive bomber). Maneuverability was to be equal to that of a Zero (A6M) fighter, to give the Ryusei reasonable immunity from interception. Normal range was to be 1000nm (maximum 1800nm). The prototype was completed in May 1942. Note that the operational concept considerably predated Midway. Production seems to have been hampered by slow engine development, as it did not begin until April 1944.

In June 1944, IJN Taihō, the only Imperial Japanese Navy aircraft carrier then large enough to operate the B7A Ryusei in its intended role, was sunk during the Battle of the Philippine Sea before enough B7As were even available to embark. Thereafter, the B7A was relegated to operating from land bases, primarily with the Yokosuka and 752nd Air Groups. The Japanese completed only one other carrier capable of operating the B7A, IJN Shinano, but she was sunk by an American submarine. Around 110 Ryusei aircraft were completed.

US Hellcats from VF-15 flying off USS Essex attack a formation of ‘Jills’ and ‘Zeros’, 19 June 1944. (Jim Laurier © Osprey Publishing)

Philippine Sea – The End of IJN Carrier Power

The encounter in the Philippine Sea was almost exclusively a carrier battle, the fifth of the Pacific War and by far the largest ever fought. Fifteen fleet and light carriers took part on the American side and nine on the Japanese. For sheer size alone, the Battle of the Philippine Sea was the second largest naval engagement of the Pacific War, surpassed only by the Battle of Leyte Gulf fought a few months later.

In line with the planning for the seizure of the Marianas, the US Navy expected a major reaction from the Imperial Japanese Navy. As a result, the destruction of the Japanese carrier fleet was one of the operation’s primary objectives. The Japanese Navy had been hoarding its carriers for almost 20 months, and its commitment to defend the Marianas was planned to be a decisive encounter with the US Navy.

Admiral Raymond A. Spruance, commander of the US Fifth Fleet, had the primary mission of conducting the Marianas invasion (Operation Forager) and defeating any Japanese naval reaction. Spruance issued his plan on 12 May 1944: the Fifth Fleet’s mission was to capture Saipan, Tinian and Guam while being ready to ‘drive off or destroy enemy forces attempting to interfere with the movement to or the landing operations at each objective.’ To achieve this, Task Force 58 would take up position to the west of the Marianas, ready to respond to any Japanese counter-attack.

On 15 June 1944, in response to the preliminary air and naval attacks on Saipan, Tinian and Guam, the Japanese activated Operation A-Go to defend the Marianas. The Japanese First Mobile Fleet, under Vice Admiral Ozawa Jisaburo, departed the Guimaras and entered the Philippine Sea later that day, where it was spotted by an American submarine. Two days later, the fleet was again spotted, this time by the submarine Cavalla, 700 nautical miles west of Guam, and by 18 June it was within 400 nautical miles of US Task Force 58. By now, Spruance had decided to await the Japanese fleet and fight a defensive battle.

A first wave of Japanese search aircraft was launched at 4.45am on 19 June, and gained contact with Task Force 58. The first Japanese strike raid against Task Force 58 comprising 69 aircraft was launched at 8.30am; US radar picked up the raid while still 125 nautical miles distant, and just after 10.20am, Task Force 58 launched all available fighters. The first Japanese attack aircraft were intercepted just over ten minutes later. Only 17 aircraft would eventually return to the Japanese carriers.

The second Japanese strike force, featuring the best-trained aviators in the First Mobile Fleet and consisting of 128 aircraft (48 ‘Zero’ fighters, 53 ‘Judy’ dive-bombers and 27 ‘Jills’ with torpedoes), left the Japanese carriers at 8.56am, and comprised the largest Japanese attack of the day. The flight was detected by US radar at 11.07am. It suffered even greater losses than the first attack wave: a mere 31 planes made it back out of the original 128.

The third attack launched at 10.00am, comprising 15 fighters, 25 ‘Zeros’ with bombs, and seven ‘Jills’ with torpedoes. From this wave, 40 out of 47 aircraft returned to the ships, chiefly because the contact location given to the aircrews turned out to be erroneous with no US ships present; seven of the returning aircraft were intercepted by US fighters, however, and shot down.

A fourth Japanese attack was launched at 11.00am, comprising 30 ‘Zero’ fighters, ten ‘Zeros’ with bombs, 36 dive-bombers (27 ‘Vals’ and nine ‘Judys’) and six ‘Jills’. These 82 aircraft were directed at another non-existent contact and, after finding nothing, split into three smaller groups. The final tally was dismal: only nine returned to their carriers, with 30 of them having been shot down over Guam. Despite these heavy losses, no American ships were hit.

Some of the Japanese attack aircraft did make it through to the US ships. In Task Group 58.7, one hit was scored on the battleship USS South Dakota and near misses were recorded on two of its cruisers just before 10.50am, from Japanese aircraft in the first attack wave. Around 12.00pm, remnants of the second Japanese attack inflicted minor damage on the carriers USS Wasp and Bunker Hill.

US submarines also inflicted damage on the First Mobile Fleet. At 9.09am, the Japanese carrier Taiho was hit by a torpedo from the submarine Albacore, and at 12.22pm the submarine Cavalla torpedoed the carrier Shokaku. The latter sank just after 3.00pm with heavy loss of life. A massive explosion ripped apart the Taiho at 3.32pm, and she followed Shokaku to the bottom.

By the end of 19 June, Task Force 58 was heading west to engage the Japanese First Mobile Fleet. Morning searches the following day failed to locate the carrier force, but at 3.40pm it was finally spotted and Spruance decided to launch an all-out attack with 216 US aircraft. Once detected, the First Mobile Fleet took evasive action to the north-west in an attempt to avoid the attack. Between 6.40 and 7.10pm, the US aircraft made a series of hasty attacks on the First Mobile Fleet, striking the carrier Hiyo with a torpedo, and damaging two other carriers, two escorts and two oilers. The Hiyo sank just after 8.30pm. Shortly after, Vice Admiral Ozawa was ordered to break off action and head for Okinawa, and the following day, Spruance ordered Task Force 58 to abandon its pursuit of the First Mobile Fleet.

The Battle of the Philippine Sea was certainly a decisive encounter. In only ten days in mid-June, the Americans realized all their major objectives and the Japanese Navy suffered a major defeat. Most of its carriers escaped, but their aircraft and trained aircrews did not. This effectively meant the end of the Japanese Navy as a major threat to future American moves in the Pacific, and led directly to the desperate and ill-conceived Japanese plan to defend Leyte in October that resulted in the final destruction of the Japanese Navy.

The Battle of the Philippine Sea clearly demonstrated to key leaders in the Imperial Japanese Navy that there was no future in conventional air attacks against the US Navy. The solution was the adoption of suicide missions that would increase in ferocity until the end of the war.

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