Yokosuka D4Y Suisei (Comet) ‘Judy’

The Yokosuka D4Y Suisei (Comet) 'Judy' was designed as a dive bomber, but entered service as a reconnaissance aircraft. It eventually served in that role, and as a bomber and suicide attack aircraft.

The D4Y was inspired by the Heinkel He 118 dive bomber, which had been entered into the same German design contest as the Junkers Ju 87 Stuka. The Germans had rejected the He 118 after one prototype fell apart while being tested by Ernst Udet, but in 1938 the Japanese imported He 118V4. This aircraft, with the Japanese designation DXHe1, underwent tests at Yokosuka. The Japanese Navy was impressed with its speed and general performance, and ordered it into production as a carrier attack aircraft. However the flaws with the design had still not been solved, and the DXHe1 also fell apart in flight.

The Navy decided to abandon production of the He 118 and instead issued a specification for a new aircraft inspired by the German design. The 13-Shi Carrier Bomber specification called for an aircraft with a maximum speed of 322mph, a cruising speed of 265mph, a range of 921 miles with a 551lb payload and 1,381 miles without a bomb. It also had to be capable of operating from smaller aircraft carriers. The aircraft was to replace the Aichi D3A 'Val'.

The He 118 was a low-wing single engined dive bomber, with elliptical inverted gull wings, and curved tail surfaces. It carried its bombload externally. It was originally powered by the Daimler-Benz DB 600 12-cylinder liquid-cooled piston engine, although the aircraft imported into Japan may have used the similar DB 601.

The Yokosuka team produced an aircraft that was smaller than the He 118 in every dimension, and significantly lighter, both empty and loaded. At the same time they designed a more aerodynamic airframe, and managed to install both larger fuel tanks and an internal bomb bay that could carry a single 1,102lb bomb.

It was originally planned to power the prototype with the Aichi Atsuta twelve-cylinder liquid-cooled engine, a licence built copy of the Daimler-Benz DB 601A. As was so often the case plans to use an untested engine caused problems, and the five prototypes used imported 960hp DB 600G engines.

The first prototype was completed in November 1940 and made its maiden flight in December 1940. It outperformed expectations, and another four prototypes were ordered. Plans were also put in place for putting the aircraft into full scale production at Aichi's Nagoya plant. These all fell apart when the aircraft was belatedly put through rigorous diving bombing tests. These revealed serious problems with the wing - wing flutter developed in the dive, causing cracks in the wing spars. Although Yokosuka and Aichi rushed to try and fix these problems, it was clear that the aircraft couldn't be used as a dive bomber.

In the meantime the first pre-production D4Y1s began to leave the Aichi production line in the spring of 1942. Luckily a role was available for the new aircraft - it was faster than the Nakajima B5N2 then being used as a reconnaissance aircraft, and so work began on installing a K-8 camera in the aft fuselage. The modified aircraft was designated the D4Y1-C.

Two pre-production D4Y1-Cs were present on the carrier Soryu during the Battle of Midway. They were lost when the carrier was sunk, but despite this setback the aircraft was ordered into production as the Navy Type 2 Carrier Reconnaissance Plane Model 11. The D4Y1-C remained in service as a carrier borne reconnaissance aircraft for the rest of the Second World War. It generally performed well, although its lack of armour made it increasingly vulnerable as Allied air power increased.

Eventually the extra work paid off and the wing problems were solved. In March 1943 the dive bomber version was accepted for service as the Suisei (Comet) Carrier Bomber D4Y1 Model 11.

The D4Y was also produced as a kamikaze attack aircraft (D4Y4) and a night fighter (D4Y2-S). During the production run the aircraft was modified to use a radial engine (D4Y3 onwards), which increased reliability.

Although the D4Y was more capable than the Aichi D3A 'Val', it still suffered from a lack of protection for the crew or the fuel tanks. It was committed to battle in large numbers during the Battle of the Philippine Sea (June 1944). A total of 141 of the dive bomber variant and 33 of the reconnaissance aircraft were onboard nine Japanese carriers during the battle. These were all of the D4Y1, D4Y1 Kai and D4Y1-C variants. During the battle the Suiseis were intercepted before they could reach the American fleet, and large numbers of them were shot down without inflicting any damage on the American fleet. The un-armoured D4Ys continued to suffer heavy losses during the fighting on and around the Philippines. Many of the surviving aircraft were then used as kamikaze aircraft. The last Suisei sortie of the war was a kamikaze mission, involving eleven aircraft led by Admiral Ugaki on 15 August 1945.

The Suisei was also turned into a night fighter, the Suisei-E D4Y2-S. This was designed for use against low flying B-29s, but the aircraft didn't carry radar and performed poorly in the night fighter role.

2,038 D4Ys were built between 1940 and 1945, mainly by Aichi. The Yokosuka arsenal built the first five prototypes in 1940-41. Aichi built 660 D4Y1s (Spring 1942-April 1944), 326 D4Y2s (April-August 1944), 536 D4Y3s (May 1944-February 1945) and 296 D4Y4s (February-August 1945). The split between dive bomber and reconnaissance versions isn't recorded.

The 11th Naval Arsenal at Hiro produced 215 D4Ys between April 1944 and July 1945, building a mix of D4Y1s, D4Y2s and D4Y3s.

Bomber Variants

D4Y1 Model 11

The D4Y1 was the first production version of the dive bomber. It was powered by a 1,200hp Atsuta 12 engine, armed with two 7.7mm machine guns and one 7.92mm machine gun. The D4Y1 family was the most numerous version of the D4Y, with 660 produced at Aichi between the spring of 1942 and April 1944.

D4Y1 Kai Model 21

The D4Y1 Kai Model 21 had catapult equipment installed to allow it to operate from the smaller carriers that were becoming increasingly important as the Japanese fleet carriers were lost.

D4Y2 Model 12

The D4Y2 used a 1,400hp Aichi AE1P Atsuta 32 engine. It entered production in October 1944, and was the fastest carrier-borne dive bomber to see service during the Second World War. Unfortunately for its crews it didn’t feature improved armour for the crews or the fuel tanks and so was still vulnerable to Allied aircraft.

D4Y2a Model 12A

The D4Y2a was similar to the D4Y2, but with a rear firing 13mm Type 2 machine gun in place of the 7.92mm gun used in earlier versions.

D4Y2 Kai Model 22

The D4Y2 Kai Model 22 had the 1,400hp Aichi Atsuta 32 engine and catapult equipment.

D4Y2a Kai Model 22A

The D4Y2a Kai Model 22A had the 1,400hp engine, catapult equipment and 13mm rear-firing machine gun.

D4Y3 Suisei Carrier Bomber Model 33

The vast majority of Japanese naval aircraft used radial engines, and the Navy was never entirely happy with the licence-built DB601. Aichi suggesting modifying the D4Y to use the Mitsubishi MK8P Kinsei 62 fourteen-cylinder radial engine. One prototype was built, with a smoothly tapering cowling to reduce drag. This aircraft underwent tests in May 1944 and performed just as well as the D4Y2. The larger engine reduced visibility during landings, but the increase in reliability was considered worth the risk. The modified aircraft was ordered into production as the Suisei Carrier Bomber Model 33 D4Y3. Late production aircraft also got three solid rocket assisted take off units to help them operate from smaller carriers.

D4Y3a Model 33A

The D4Y3a Model 33A was similar to the D4Y3, but as with the D4Y2a was armed with a rear firing 13mm machine gun in place of the normal 7.7mm machine gun.

D4Y4 Suisei Special Attack Bomber Model 43

The D4Y4 Suisei Special Attack Bomber Model 43 was a suicide attack version of the aircraft. It was powered by the Kinsei radial engine, carried a single 1,764lb bomb partly carried within the fuselage. It only carried a pilot to save weight. It had the rocket assisted take off units, which could be used either at take off, or to increase the speed of the final attack. A total of 286 D4Y4s were built during 1945.

D4Y5 Model 54

The D4Y5 was under development at the end of the war. It finally addressed the lack of armour, introducing protection for the crew and the fuel tanks. It was to be powered by the 1,825hp Nakajima NK9C Homare 12 eighteen-cylinder air cooled engine, but it wasn't due to enter production until the end of 1945.

Reconnaissance Variants

D4Y1-C

The D4Y1-C was the first version to see active service. It was powered by a 1,200hp Aichi Atsuta 12 engine, and carried a single camera in the rear fuselage. It was soon overshadowed by production of the dive-bomber variants.

D4Y2-C Navy Type 2 Carrier Reconnaissance Plane Model 12

The D4Y2-C was a reconnaissance aircraft version of the D4Y2, with a 1,400hp Aichi Atsuta 32 engine.

D4Y2-Ca Navy Type 2 Carrier Reconnaissance Plane Model 12A

The D4Y2-Ca was the reconnaissance version of the D4Y2a with a rear firing 13mm machine gun.

There were no reconnaissance versions of the D4Y3 as the superior Nakajima C6N1 had entered service.

Other Variants

D4Y2-S Suises-E Night Fighter

The D4Y2-S night fighter was produced to operate against low flying B-29s. The bomb racks, rear firing guns and carrier equipment were all removed to save weight. One obliquely mounted 20mm Type 99 Model 2 cannon was installed in the fuselage, firing up and forward at 30 degrees. The aircraft could also carry air-to-air rockets. The D4Y2-S didn't have radar and it didn't perform well as a night fighter.

Stats

D4Y1
Engine: Aichi AE1A Atsuta 12 twelve-cylinder inverted V liquid cooled engine
Power: 1,200hp at take off
Crew: 2
Span: 37ft 8 3/4in
Length: 33ft 6 3/8in
Height: 12ft 0 11/16in
Empty weight: 5,379lb
Maximum take-off weight: 9,370lb
Max speed: 343mph at 15,585ft
Climb Rate: 5min 14sec to 9,845ft
Service ceiling: 32,480ft
Range: 978 miles
Armament: Two fixed forward firing 7.7mm Type 97 machine guns and one rear-firing flexibly mounted 7.92mm Type 1 machine gun
Bomb load: 683lb normal, 1,234lb maximum

D4Y2
Engine: Aichi AE1P Atsuta 32 twelve-cylinder inverted V liquid cooled engine
Power: 1,400hp at take-off
Crew: 2
Span: 37ft 8 3/4in
Length: 33ft 6 3/8in
Height: 12ft 3 1/4in
Empty weight: 5,809lb
Maximum take-off weight: 10,192lb
Max speed: 360mph at 17,225ft
Climb Rate: 4min 36sec to 9,845ft
Service ceiling: 35,105ft
Range: 909 miles
Armament: Two fixed forward firing 7.7mm Type 97 machine guns and one rear-firing flexibly mounted 7.92mm Type 1 machine gun
Bomb load: 683lb normal, 1,234lb maximum

D4Y3
Engine: Mitsubishi MK8P Kinsei 62 fourteen-cylinder air-cooled radial engine
Power: 1,400hp at take-off
Crew: 2
Span: 37ft 8 3/4in
Length: 33ft 6 3/8in
Height: 12ft 3 1/4in
Empty weight: 5,515lb
Maximum take-off weight: 10,267lb
Max speed: 357mph at 19,850ft
Climb Rate: 4min 35sec to 9,845ft
Service ceiling: 34,450ft
Range: 944 miles
Armament: Two fixed forward firing 7.7mm Type 97 machine guns and one rear-firing flexibly mounted 7.92mm Type 1 machine gun
Bomb load: 683lb normal, 1,234lb maximum

D4Y4
Engine: Mitsubishi MK8P Kinsei 62 fourteen-cylinder air-cooled radial engine
Power: 1
Crew: 1,400hp at take-off
Span: 37ft 8 3/4in
Length: 33ft 6 3/8in
Height: 12ft 3 1/4in
Empty weight: 5,809lb
Maximum take-off weight: 10,463lb
Max speed: 350mph at 19,355ft
Climb Rate: 9min 22sec to 16,405ft
Service ceiling: 27,725ft
Range: 1,024 miles
Armament: Two fixed forward firing 7.7mm Type 97 machine guns
Bomb load: 1,764lb

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How to cite this article: Rickard, J (2 June 2015), Yokosuka D4Y Suisei (Comet) ‘Judy’ , http://www.historyofwar.org/articles/weapons_yokosuka_D4Y_suisei.html

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