The Yokosuka D4Y Suisei, known as “Judy” by Allied forces, was a two-seat carrier-based dive bomber developed by the Yokosuka Naval Air Technical Arsenal and utilized by the Imperial Japanese Navy during World War II from 1942 to 1945.
The aircraft’s development commenced in 1938, with the first D4Y1 being completed in November 1940 and undergoing its maiden flight at Yokosuka the following month.
Although initially designed as a dive bomber, the D4Y was employed in various other roles, including reconnaissance, night fighter, and special attack (kamikaze).
The aircraft’s combat debut occurred as a reconnaissance plane when two pre-production D4Y1-Cs were deployed aboard the Sōryū to participate in the Battle of Midway in 1942.
It was not until March 1943 that the D4Y was approved for use as a dive bomber.
The early D4Y1 and D4Y2 models featured the liquid-cooled Aichi Atsuta engine, a licensed version of the German Daimler-Benz DB 601, while the later D4Y3 and D4Y4 models were equipped with the Mitsubishi MK8P Kinsei radial engine.
Similar to many other Japanese aircraft of the time, the D4Y lacked armour and self-sealing fuel tanks.
It was not until the final variant, the D4Y4, that the aircraft was fitted with bulletproof glass and armour protection for the crew and fuel tanks.
Despite this, the D4Y was one of the fastest dive bombers of the war, with the D4Y4 being the “fastest dive-bomber of World War II,” according to Max Gadney, and faster than the Zero.
The delays in its development hindered its service, while its predecessor, the slower fixed-gear Aichi D3A, remained in service much longer than intended.
Notably, a D4Y was used in one of the final kamikaze attacks in 1945, hours after Japan’s surrender, with Vice Admiral Matome Ugaki in the rear cockpit.
The development of the aircraft began in 1938 at the Yokosuka Naval Air Technical Arsenal when the Imperial Japanese Navy Aviation Bureau (Kaigun Kōkū Hombu) issued requirements for a Navy Experimental 13-Shi Carrier Borne specification for an aircraft carrier-based dive bomber to replace the Aichi D3A.
The 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 that provided excellent 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 (1,200 hp).
The radiator was behind and below the three-blade propeller.
The aircraft had a slim fuselage that enabled it to reach high speeds in horizontal flight and in dives, while it had excellent manoeuvrability 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.
Consequently, 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 (1,100 lb) bomb, but there were reports that the D4Y sometimes carried two 250 kg (550 lb) bombs.
The aircraft was armed with two 7.7 mm (.303 in) Type 97 aircraft machine guns in the nose and a 7.92 mm (.312 in) Type 1 machine gun – selected for its high rate of fire – in the rear of the cockpit. The rear gun was replaced by a 13 mm (.51 in) Type 2 machine gun.
This armament was typical for Japanese carrier-based dive-bombers, unlike “carrier attack bombers” (torpedo bombers) like the Nakajima B5N and B6N, which were not given forward-firing armament until the late-war Aichi B7A, which was expected to serve as both a dive-bomber and torpedo-bomber and was given a pair of 20mm Type 99-2 cannon.
The forward machine guns were retained in the kamikaze version.
Variants
D4Y1 Experimental Type 13 carrier dive-bomber
5 prototypes were produced.
3 and 4 were rebuilt to reconnaissance plane and carried on aircraft carrier Sōryū.
D4Y1-C Type 2 reconnaissance aircraft Model 11
Reconnaissance version produced at Aichi’s Nagoya factory.
Developed on 7 July 1942.
D4Y1 Suisei Model 11
First batch of serial produced dive bomber aircraft.
D4Y3 with the rear cockpit 13 mm (.51 in) machine gun.
D4Y3 Suisei Model 33 night-fighter variant
Temporary rebuilt night-fighter version.
Two planes were converted from D4Y3, Equipment was a 20 mm upward-firing cannon.
D4Y4 Suisei Model 43
Final production variant.
Bomb load increased to 800 kg (1,760 lb) with the main bomb semi-recessed in the bomb bay.
It had 75 mm bullet-proof glass in front of the canopy, plus 5mm and 9mm thick armour plates fore and aft of the cockpit.
The fuel tanks were also given added protection, and the movable rear machine gun was removed.
The addition of five RATO boosters was considered: three in the lower-bottom part of the fuselage and two on both sides below the engine.
Generally, the D4Y4 is often recognized as being purpose-built for special attack operations.
D4Y5 Suisei Model 54
Planned version with Nakajima Homare radial engine, four-blade propeller, and more armour protection.
Specifications
Crew
2
Length
10.22 m (33 ft 6 in)
Wingspan
11.5 m (37 ft 9 in)
Height
3.74 m (12 ft 3 in)
Wing area
23.6 m2 (254 sq ft)
Empty weight
2,440 kg (5,379 lb)
Gross weight
4,250 kg (9,370 lb)
Powerplant
1 × Aichi Atsuta AE1P 32,
V-12 inverted liquid-cooled piston engine,
1,000 kW (1,400 hp)
Performance
Maximum speed
550 km/h (340 mph, 300 kn)
Range
1,465 km (910 mi, 791 nmi)
Service ceiling
10,700 m (35,100 ft)
Rate of climb
14 m/s (2,800 ft/min)
Wing loading
180 kg/m2 (37 lb/sq ft)
Power/mass
025 kW/kg (15 hp/lb)
Armament
Guns
2× forward-firing 7.7 mm Type 97 aircraft machine guns
1× rearward-firing 7.92 mm Type 1 machine gun
Bombs
500 kg (1,100 lb) of bombs (design)
800 kg (1,800 lb) of bombs.
Sources Japanese Aircraft, 1910-1941-Robert Mikesh & Shorzoe Abe The Mainichi Newspapers Co Ltd Yushukan War Memorial Museum Japanese Aircraft of the Pacific War-Rene Francillon, Japanese Aircraft-John Stroud, Japanese Military Aircraft Illustrated.
