Yokosuka D4Y Suisei

The Yokosuka D4Y Suisei is a two-seat carrier-based dive bomber. It was developed by the Yokosuka Naval Air Technical Arsenal and operated by the Imperial Japanese Navy from 1942 to 1945 during World War II. Development of the aircraft began in 1938. The first D4Y1 was complete in November 1940 and made its maiden flight at Yokosuka the following month.
While the aircraft was originally conceived as a dive bomber, the D4Y was used in other roles including reconnaissance, night fighter and special attack. It made its combat debut as a reconnaissance aircraft when two pre-production D4Y1-Cs embarked aboard the Sōryū to take part in the Battle of Midway in 1942. It was not until March 1943 that it was accepted for use as a dive bomber. The early D4Y1 and D4Y2 featured the liquid-cooled Aichi Atsuta engine, a licensed version of the German Daimler-Benz DB 601, while the later D4Y3 and D4Y4 featured the Mitsubishi MK8P Kinsei radial engine.
Like many other Japanese aircraft of the time, the D4Y lacked armor and self-sealing fuel tanks and it was not until the final variant, the D4Y4, that the aircraft was given bulletproof glass and armor protection for the crew and fuel tanks. Nevertheless, the D4Y was one of the fastest dive bombers of the war, particularly the D4Y4 which Max Gadney said was the "fastest dive-bomber of World War II" and that it was "faster than the Zero". Only the delays in its development hindered its service while its predecessor, the slower fixed-gear Aichi D3A, remained in service much longer than intended. In October 1944, an attack by a lone D4Y resulted in the sinking of light carrier USS Princeton in the Battle of Leyte Gulf. Similarly in March 1945, a single D4Y managed to hit the carrier USS Franklin with two bombs, nearly sinking Franklin and resulting in the loss of almost 800 of her crew. Famously, a D4Y was used in one of the final kamikaze attacks in 1945, hours after the surrender of Japan, with Vice Admiral Matome Ugaki in the rear cockpit.

Design and development

Development of the aircraft began in 1938 at the Yokosuka Naval Air Technical Arsenal when the Imperial Japanese Navy Aviation Bureau issued requirements of a Navy Experimental 13-Shi Carrier Borne specification for an aircraft carrier-based dive bomber to replace the Aichi D3A. Its design was inspired by the Heinkel He 118 which the Japanese Navy had acquired from Germany in early 1938. The aircraft was a single-engine, all-metal low-wing monoplane, with a wide-track retractable undercarriage and wing-mounted dive brakes. It had a crew of two: a pilot and a navigator/radio-operator/gunner, seated under a long, glazed canopy which provided good all-round visibility. The pilot of bomber versions was provided with a telescopic bombsight. The aircraft was powered by an Aichi Atsuta liquid-cooled inverted V12 engine, a licensed copy of the German Daimler-Benz DB 601, rated at 895 kW. The radiator was behind and below the three-blade propeller, as in the Curtiss P-40 Warhawk.
The aircraft had a slim fuselage that enabled it to reach high speeds in horizontal flight and in dives, while it had excellent maneuverability despite high wing loading, with the Suisei having superior performance to contemporary dive bombers such as the Curtiss SB2C Helldiver. In order to conform with the Japanese Navy's requirement for long range, weight was minimized by not fitting the D4Y with self-sealing fuel tanks or armour. Subsequently, the D4Y was extremely vulnerable and tended to catch fire when hit.
Bombs were fitted under the wings and in an internal fuselage bomb bay. It usually carried one 500 kg bomb but there were reports that the D4Y sometimes carried two 250 kg bombs.

Operational history

Lacking armor and self-sealing fuel tanks, the Suiseis did not fare well against Allied fighters. They did, however, cause considerable damage to ships, including the carrier which was nearly sunk by an assumed single D4Y and the light carrier which was sunk by a single D4Y.
The D4Y was operated from the following Japanese aircraft carriers:,,,,,,,,, and.
The D4Y1-C reconnaissance aircraft entered service in mid-1942, when two of these aircraft were deployed aboard Sōryū at the Battle of Midway, one of which was lost when Sōryū was bombed. The other had been launched on a scouting mission and returned to Hiryū; it was then lost when Hiryū was bombed.

Marianas

During the Battle of the Marianas, the D4Ys were engaged by U.S. Navy fighters and shot down in large numbers. It was faster than the Grumman F4F Wildcat, but not the new Grumman F6F Hellcat, which entered combat in September 1943. The Japanese aircraft were adequate for 1943, but the rapid advances in American materiel in 1944 left the Japanese behind. Another disadvantage suffered by the Japanese was their inexperienced pilots.
The U.S. Task Force 58 struck the Philippine airfields and destroyed the land air forces first before engaging Japanese naval aircraft. The result was what the Americans called "The Great Marianas Turkey Shoot", with 400 Japanese aircraft shot down in a single day. A single Hellcat pilot, Lieutenant Alexander Vraciu, shot down six D4Ys within a few minutes.
One D4Y was said to have damaged the battleship.

Leyte and Philippines

The D4Y was relegated to land operations where both the liquid-cooled engine D4Y2, and the radial engine D4Y3 fought against the U.S. fleet, scoring some successes. An unseen D4Y bombed and sank the Princeton on 24 October 1944. D4Ys hit other carriers as well, by both conventional attacks and kamikaze actions. In the Philippines air battles, the Japanese used kamikazes for the first time, and they scored heavily. D4Ys from 761 Kōkūtai may have hit the escort carrier on 25 October 1944, and the next day,. Both were badly damaged, especially Suwannee, with heavy casualties and many aircraft destroyed. A month later on 25 November,,, and were hit by kamikazes, almost exclusively A6M Zero fighters and D4Ys, with much more damage. D4Ys also made conventional attacks. All these D4Ys were from 601 and 653 Kōkūtai.

In defense of the homeland

Task Force 58 approached southern Japan in March 1945 to strike military objectives in support of the invasion of Okinawa. The Japanese responded with massive kamikaze attacks, codenamed Kikusui, in which many D4Ys were used. A dedicated kamikaze version of the D4Y3, the D4Y4, with a non-detachable 800 kg bomb attached in a semi-recessed manner, was developed. The Japanese had begun installing rocket boosters on some Kamikazes, including the D4Y4, in order to increase speed near the target. As the D4Y4 was virtually identical in the air to the D4Y3, it was difficult to determine the sorties of each type.
The carriers and were damaged by D4Ys of 701 Wing on 18 March. On 19 March, the carrier was hit with two bombs from a single D4Y. Franklin was so heavily damaged that she was retired until the end of the war. Another D4Y hit the carrier.
On 12 April 1945, another D4Y, part of Kikusui mission N.2, struck Enterprise, causing some damage.
During Kikusui N.6, on 11 May 1945, was hit and put out of action by two kamikazes that some sources identify as D4Ys. This was the third Essex-class carrier forced to retire to the United States to repair.

Night fighter

The D4Y was faster than the A6M Zero, and some were employed as D4Y2-S night fighters against Boeing B-29 Superfortress bombers late in the War. The night fighter conversions were made at the 11th Naval Aviation Arsenal at Hiro. Each D4Y2-S had its bombing systems and equipment removed and replaced by a 20 mm Type 99 cannon installed in the rear cockpit, with the barrel slanted up and forwards in a similar manner to the German Schräge Musik armament fitting. Some examples also carried two or four 10 cm air-to-air rockets under the wings; lack of radar for night interceptions, inadequate climb rate and the B-29's high ceiling limited the D4Y2-S effectiveness as a night fighter. Little is known of their operations.

Last action

At the end of the War, D4Ys were still being used operationally against the U.S. Navy. Among the last of these were eleven aircraft led by Vice Admiral Matome Ugaki on a suicide mission on 15 August 1945, of which all but three were lost.

Operators

Imperial Japanese Navy Air Service
Aircraft carrier
* Sōryū, equipped prototype #2 and #3.
* Shōkaku, supplied from 601st Kōkūtai.
* Zuikaku, supplied from 601st Kōkūtai.
* Taihō, supplied from 601st Kōkūtai.
* Jun'yō, supplied from 652nd Kōkūtai.
Battleship
* Ise, supplied from 634th Kōkūtai.
* Hyūga, supplied from 634th Kōkūtai.
Naval Air Group
* Himeji Kōkūtai
* Hyakurihara Kōkūtai
* Kaikō Kōkūtai
* Kanoya Kōkūtai
* Kantō Kōkūtai
* Kinki Kōkūtai
* Kyūshū Kōkūtai
* Nagoya Kōkūtai
* Nansei-Shotō Kōkūtai
* Ōryū Kōkūtai
* Tainan Kōkūtai
* Taiwan Kōkūtai
* Tōkai Kōkūtai
* Tsuiki Kōkūtai
* Yokosuka Kōkūtai
* 12th Kōkūtai
* 121st Kōkūtai
* 131st Kōkūtai
* 132nd Kōkūtai
* 141st Kōkūtai
* 151st Kōkūtai
* 153rd Kōkūtai
* 201st Kōkūtai
* 210th Kōkūtai
* 252nd Kōkūtai
* 302nd Kōkūtai
* 352nd Kōkūtai
* 501st Kōkūtai
* 502nd Kōkūtai
* 503rd Kōkūtai
* 521st Kōkūtai
* 523rd Kōkūtai
* 531st Kōkūtai
* 541st Kōkūtai
* 552nd Kōkūtai
* 553rd Kōkūtai
* 601st Kōkūtai
* 634th Kōkūtai
* 652nd Kōkūtai
* 653rd Kōkūtai
* 701st Kōkūtai
* 721st Kōkūtai
* 722nd Kōkūtai
* 752nd Kōkūtai
* 761st Kōkūtai
* 762nd Kōkūtai
* 763rd Kōkūtai
* 765th Kōkūtai
* 901st Kōkūtai
* 951st Kōkūtai
* 1001st Kōkūtai
* 1081st Kōkūtai
Aerial Squadron
* Reconnaissance 3rd Hikōtai
* Reconnaissance 4th Hikōtai
* Reconnaissance 61st Hikōtai
* Reconnaissance 101st Hikōtai
* Reconnaissance 102nd Hikōtai
* Attack 1st Hikōtai
* Attack 3rd Hikōtai
* Attack 5th Hikōtai
* Attack 102nd Hikōtai
* Attack 103rd Hikōtai
* Attack 105th Hikōtai
* Attack 107th Hikōtai
* Attack 161st Hikōtai
* Attack 251st Hikōtai
* Attack 263rd Hikōtai
Kamikaze
* Chūyū group
* Giretsu group
* Kasuga group
* Chihaya group
* Katori group
* Kongō group No. 6
* Kongō group No. 9
* Kongō group No. 11
* Kongō group No. 23
* Kyokujitsu group
* Suisei group
* Yamato group
* Kikusui-Suisei group
* Kikusui-Suisei group No. 2
* Koroku-Suisei group
* Chūsei group
* Mitate group No. 3
* Mitate group No. 4
* 210th group
* Niitaka group
* Yūbu group
United States Navy operated captured aircraft for evaluation purposes.

Variants

;D4Y1 Experimental Number 13 carrier dive-bomber
;D4Y2 Suisei Model 12
;D4Y3 Suisei Model 33
;D4Y4 Suisei Model 43
;Suisei Model 54

Surviving aircraft

In 1988, a restored D4Y1 was donated to the Yasukuni Shrine Yūshūkan Museum in Tokyo, where it remains on display. The wreck was recovered from Colonia Airfield on Yap Island and restored at Kisarazu Air Field from 1979 to 1980.
An engineless D4Y3 was recovered from Babo Airfield, Indonesia in 1991. It was acquired and restored to non-flying status by the Planes of Fame Air Museum in Chino, California. It was restored to represent a radial engined D4Y3, using an American Pratt & Whitney R-1830 engine. The engine is in running condition and can be started to demonstrate ground running and taxiing of the aircraft.