YOKOSUKA D4Y

The 'Yokosuka D4Y ''Suisei''' (彗星, "comet") was a dive bomber of the Imperial Japanese Navy. Its Allied codename was "Judy".

Contents

Design and development

Technical description

Variants

Operational history

Overview

Marianas

Leyte and Philippines

In defence of the homeland

Operators

Specifications (D4Y2)

References

External links

Related content

Design and development

Development of the aircraft began in 1938 at the Yokosuka Naval Air Technical Arsenal, based on two Heinkel He 118 dive bombers that had been supplied by Germany. The first D4Y1 prototype made its maiden flight in December 1940, and proved to possess an excellent combination of high performance and good handling. After the prototype's successful trials, development continued, and the first problems appeared. During dive-bombing trials the wings of the D4Y started to flutter, a fatal flaw for an airframe subject to the stresses of dive bombing, and initial models were used only as reconnaissance aircraft. Two of these aircraft joined the fleet in mid-1942 in time for the Battle of Midway, where one was used in action. The structural problems were finally fixed by March 1943, and ultimately 2,038 were produced, mostly by Aichi.
Early versions of the D4Y were difficult to keep in service since the liquid-cooled Atsuta in-line inverted-V12 engines were unreliable and difficult to maintain. 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.
As soon as time permitted, the Aichi design team looked for a radial engine, and the Mitsubishi MK8P Kinsei 62 fourteen-cylinder two-row radial engine, rated at 1,560 hp (1,163 kW), was selected. This resulted in the Yokosuka D4Y3 Model 33. However, the larger radial engine obstructed the forward and downward view of the pilot, hampering carrier operations.
The D4Y series of dive bombers were very fast for this type of aircraft and some were even converted to night fighters against the high flying B-29 bombers later in the war. At the 11th Naval Aviation Arsenal at Hiro, the Japanese attempted to make a D4Y2-S night fighter: all bomb equipment was removed and a 20 mm Type 99 Model 2 cannon with its barrel slanting upwards was installed in the place of the gunner's cockpit - but the lack of radar and slow climb rate made it ineffective as a night fighter.

Technical description

The aircraft was capable of operating from aircraft carriers and, because of its long range, from airfields. It had a crew of two; pilot and navigator/radio-operator/gunner.
The aircraft was all metal, with a low wing, retractable undercarriage, and although built with a very light structure to be a dive bomber, was quite a robust machine. It had a slim, elegant, fine design, to enable it to reach high speeds in horizontal flight and in dives. Airbrakes were in the wings.
Its light construction made the D4Y vulnerable to any enemy aircraft that could catch it, though few could, as it was around 100 km/h faster than its US counterpart, the Curtiss SB2C Helldiver, and even faster than the UK's Fairey Barracuda. In fact, the D4Y was the fastest dive-bomber in the entire war, and only the delays in its development caused its limited service, while its predecessor, the more robust, but slower, Aichi D3A remained in service (as did its equivalent the SBD Dauntless), for years.
D4Ys were so fast (faster even than the A6M Zero fighter) that they were employed as night fighters, something that no other single-engined dive bomber was ever used for.
Bombs were fitted under the wings and in an internal bomb bay, something rare in a single-engine aircraft. It carried one 500 kg bomb, but there are reports, for example during the sinking of the USS ''Princeton'', that the aircraft could carry two 250 kg bombs. Only 30 kg bombs were carried externally.
The aircraft was armed with two 7.7 mm machine guns in the nose, and one 7.92 mm (with a higher rate of fire, which explains why two different types of light machine-guns were fitted) in the rear, later substituted with a more powerful 13 mm gun. It worth noting that the Helldiver had a much more powerful battery of two 20 mm or four 12.7 mm guns forward, while the Fairey Barracuda had no forward weapons at all. The forward machine guns were retained in the Kamikaze version, probably to fire against the naval air defence in the last seconds of the dive.
The aircraft showed extreme vulnerability and a tendency to catch fire when hit, as self-sealing fuel tanks and armor were apparently not fitted in order to extend the range of the aircraft over the ocean. This was a risky choice, and when the US fielded high-performance fighters, early warning radars and improved radio communications, the D4Y's suffered accordingly. Despite this, the speed and the range of D4Ys was nevertheless valuable and they were used with success as Kamikaze and reconnaissance aircraft.
The engine was initially the German DB 600, then an indigenous 1,200 hp Aichi Atsuta 12, while the D4Y2 had the 1,400 hp Atsuta 32. The radiator was behind and below the three-bladed propeller, as in the P-40. Finally, the D4Y3 had the reliable and more powerful 1,530 hp Kinsei 62 radial engine fitted. The additional drag did not prevent it achieving the same speed and even better performance, however visibility worsened, because of the bigger diameter of the nose. Radial engines were the most widely type used in naval aircraft (mainly for their reliability), and this aircraft was one of the few that was adapted for radial engines even if designed for inline ones.
With the radial engine the range was reduced by the higher fuel consumption, and for the same reason the cruise speed was apparently less. However ceiling and rate of climb were, for the same reason, greater (over 10,000 m, and climb to 3,000 m in 4.5 minutes, instead of 9,400 m and 5 minutes).
Among the other details, there was a glassed cockpit, with all-round visibility, a wide undercarriage and a relatively low wing load, comparable to a fighter. The aiming system in many if not all D4Y was still the 'peashooter' type, not a reflex one.

Variants

;D4Y1
:Prototype and first batch of serial produced dive bomber aircraft.
;D4Y1-C
:Reconnaissance version produced at Aichi's Nagoya factory.
;D4Y1 KAI
:Dive bomber version equipped with aircraft carrier catapult equipment.
;D4Y2 Model 12
:Powered by the Aichi AE1P Atsuta 32 inline engine (license-built Daimler-Benz DB 601) rated at 1,400 hp (1044 kW).
;D4Y2-C
:Reconnaissance version of the D4Y2.
;D4Y2 KAI Model 22
:D4Y2 version equipped with aircraft carrier catapult equipment.
;D4Y2a Model 12A
:D4Y2 with the rear cockpit 7.92 mm Type 1 machine gun replaced by the 13 mm Type 2 machine gun.
;D4Y2-Ca
:Reconnaissance version of the D4Y2a.
;D4Y2a KAI Model 22A
:D4Y2a version equipped with aircraft carrier catapult equipment.
;D4Y2-S Suisei-E
:Night fighter version with bomb equipment removed and a 20 mm Type 99 Model 2 cannon installed in place of the gunner's cockpit.
;D4Y3 Model 33
:Powered by the 14-cylinder Mitsubishi MK8P Kinsei 62 two-row radial engine rated at 1,560 hp (1,163 kW).
;D4Y3a Model 33A
:D4Y3 with the rear cockpit 7.92 mm Type 1 machine gun replaced by the 13 mm Type 2 machine gun.
;D4Y4 Model 43 Special Strike Bomber
:One seat kamikaze aircraft equipped with 800 kg bomb and 3 RATO boosters for taking off from short runways and with terminal dive acceleration.
;D4Y5 Model 54
:Planned version powered by the Nakajima JK9C Homare 12 radial engine rated at 1,825 hp (1,361 kW). Aircraft had new four-blade metal propeller of the constant-speed type and more armor protection for the crew and fuel tanks.

Operational history

Overview

Lacking armor and self-sealing fuel tanks, the Suiseis did not do well against Allied fighter aircraft. They did, however, cause considerable damage to ships, including the carrier USS ''Franklin'', which was nearly sunk by a single "D4Y".
The D4Y was operated from the following Japanese aircraft carriers: Chitose, Chiyoda, Hiyo-, Junyo-, Shinyo, Sho-kaku, So-ryu-, Taiho-, Unryu-, Unyo and Zuikaku.
The last version was the D4Y4 Special Strike Bomber Model 43. This one-seat kamikaze aircraft (scale model), capable of carrying one 800 kg bomb, was put into production in February 1945. It was equipped with three RATO boosters for taking off from short runways and for terminal dive acceleration. This aircraft was an almost ideal kamikaze model: it had a combination of speed (560 km/h), range (2,500 km) and payload (800 kg) probably not matched by any other Japanese aircraft, because the typical models used for this task were mainly Zero's, that lacked such range, payload and speed.

Marianas

During the Battle of the Marianas the DY4's were engaged by US naval fighters and shot down in large numbers. The D4Y's speed was high enough to avoid the F4F Wildcat, but not enough for the new F6F Hellcat. The Japanese aircraft were adequate in 1943, but the rapid advances in American materiel in 1944 (among them, the introduction in large numbers of the Essex class aircraft carrier) left them behind, while their inexperienced pilots were another disadvantage.
The US Task Force 58 struck the Philippine airfields and destroyed the land air forces first, before engaging the 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, piloted by Lt. Vraciu, shot down six D4Y's within a few minutes.

Leyte and Philippines

The D4Y was relegated to land operations, and there both the original liquid-cooled engine versions, and the later radial engine versions fought against the US fleet, scoring some successes. One of them was the sinking of a light carrier USS ''Princeton'', hit in October 1944 by one or two bombs released by an unseen D4Y. Other carriers were struck as well, both by conventional attacks and kamikaze actions. In the Philippines air battles the Japanese airforce used kamikazes for the first time, and they scored heavily. D4Ys from 761 Kokutai were possibly involved in the hitting of the USS ''Kalinin Bay'' (25 October 1944, the day of the battle with Kurita's ships), and the next day the USS ''Suwannee'', damaging them, especially the latter, with many killed and wounded, and many aircraft destroyed. A month later on 25 November, the USS ''Essex'', USS ''Hancock'', USS ''Intrepid'' and USS ''Cabot'' were hit by kamikazes, almost exclusively A6Ms and D4Ys, with much more damage. The D4Ys were used in such attacks, both conventional and kamikaze, also by 601 and 653 Kokutai.

In defence of the homeland

When Task Force 58 approached south Japan to strike military objectives, to help the upcoming invasion of Okinawa, there were many heavy battles with Japan, resulting in heavy losses on both sides, and the US Navy lost its long period of almost total invulnerability.
The USS ''Enterprise'' and USS ''Yorktown'' were damaged by D4Ys of 701 Wing on 18 March. On 19 March, the USS ''Franklin'' was hit by another D4Y, despite the heavy anti-aircraft fire. The ship, surprised when preparing an attack mission over Japan, had its main deck full of armed and fuelled aircraft. Over 50 aircraft were destroyed and almost 800 men were killed, many by fumes generated by the fires. The ship was so heavily damaged that she was retired until the end of the war. Another D4Y hit the USS ''Wasp'', another modern carrier.
On 12 April 1945 another D4Y, part of Kikosui mission N.2 (a massive kamikaze attack on the US Navy during the Okinawa invasion) struck USS ''Enterprise'', causing some damage.
During Kikosui N.6, on 11 May 1945, the USS ''Bunker Hill'' was hit by a pair of aircraft, that some sources identify as Zeros, others D4Ys, that struck the ship and set fire to it. Almost 400 men were killed and the ship was put out of action. This was the third Essex-class carrier forced to retire to the States to repair, 20% of the total built.
Some D4Y, in the meanwhile, tried to shoot down B-29 bombers, but the high ceiling or the night operations hindered their task and little is known actually of their operations.
At the end of the war, there were still D4Y in action against the US Navy, and maybe the last of them were the eleven D4Ys that set off on a search mission on the 15 August 1945. Led by Vice Admiral Matome Ugaki, all but three were shot down or crashed into the sea.

Operators

;

★ Imperial Japanese Navy Air Service

★
★ 1st Koku Sentai

★
★ 2nd Koku Sentai

★
★ 3rd Koku Sentai
;United States

★ United States Navy operated captured aircraft for evaluation purposes.

Specifications (D4Y2)

References

★ ''The Yokosuka D4Y Suisei'' entry at the ''World War 2 Warbirds'' website

★ Vaccari, Pierfrancesco,''Le campagne di Jwo Jima and Okinawa'', RID magazine, n.1/2002

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