Aichi D3A Val

The Aichi D3A Val aircraft was the standard dive bomber used by the Imperial Japanese Navy at the outbreak of Second World War in the Pacific. The aircraft was introduced at the end of 1939 as a successor to the Aichi D1A dive bomber. The first operational deployment took place in China in November 1939. Nearly 1,500 aircraft were produced in two variants, and from mid-1942, as a carrier-based bomber, gradually replaced from mid-1942 by the Yokosuka D4Y dive bomber. The Aichi D3A itself would continue to be used as a land-based bomber as well as a training aircraft until the end of the war.

Aichi D3A Val Source: Public Domain (unknown)

The Aichi D3A design followed the so-called 11-Shi specifications, issued by the Japanese Navy in mid-1936. The assignment involved the development of a single-plane carrier-based dive bomber, replacing the Aichi D1A2 dive bomber used so far. The companies Aichi, Nakajima and Mitsubishi all submitted their designs. Aichi and Nakajima were asked to each manufacture two prototypes of the Aichi D3A and the Nakajima D3N respectively.^[1][2]

At Aichi they designed an aircraft with low-mounted elliptical wings. Chief designer Goake Tokuichiro had used the wing characteristics of the German Heinkel He 70 and the dive braking system of the Junkers Ju 87 for the design. Due to the relatively low speed for which the aircraft was designed, a fixed landing gear was sufficient. To power the aircraft, a 709 hp (529 kW) Nakajima Hikari 1 radial engine was chosen. A first prototype was presented in December 1937, and the aircraft was put to an airborne test a month later. The first tests were not promising. The aircraft lacked sufficient power and appeared to exhibit instability when taking turns. As soon as a dive exceeded 370 km/h, the dive brakes started to vibrate seriously. This caused problems as the specifications called for a diving speed of at least 440 km/h. The second prototype was significantly modified whereby an attempt was made to increase power by using an 839 hp (626 kW) Mitsubishi Kinsei 3 engine. The horizontal tail section was enlarged to improve stability. The wingspan was slightly extended and more robust dive brakes were installed. Although not optimal, the improvements were such that they won the competition with the Nakajima.^[3][4][5]

Prototype Aichi D3A. Source: Public Domain (unknown)

Initially, the pilot availed of a Type 95 telescopic gunsight. Subsequent models received a Type 99 telescope. The observer/navigator had access to a Type 97 Mk 1 drift sight to assist the pilot and a Type 96 Mk 2 radio installation. The standard bomb load consisted of a 250 kg bomb, carried under the fuselage on a release device. Additionally, two more 60 kg bombs could be carried, one under each wing. As defensive armament, the pilot had two fixed, forward-firing 7.7 mm Type 97 machine guns at its disposal, whereas the observer had a flexible 7.7 mm Type 92 machine gun fitted at the rear of the cockpit.

The aircraft was ordered by the Japanese Navy in December 1939 and given the designation Marine Type 99 Aircraft Carrier Bomber Model 11 and the factory designation Aichi D3A1. This type would be the standard dive bomber for the Japanese Navy until June 1942. In that month a new improved type was tested and designated as Aichi D3A2 or also Marine Type 99 Aircraft Carrier Bomber Model 12 and after further improvement Model 22. Since the entry into service of the Yokosuka D5Y dive bomber, the Aichi D3A was slowly replaced on board aircraft carriers. However, the Aichi D2A continued to operate from land until the end of the Second World War and finally as a training aircraft. Several aircraft were specially adapted for the latter purpose and as such designated the Aichi D3A2-K or Marine Type 99 Bomber Trainer Model 12. In the last year of the war, many Aichi D3A aircraft were used in kamikaze missions.^[6]

When the Marine Type 99 Aircraft Carrier Bomber Model 11, or the Aichi D3A1, went int full production it was powered by a 1,000 hp (746 kW) Mitsubishi Kinsei 43 or a 1,070 hp (798 kW) Mitsubishi Kinsei 44 engine. The enlarged horizontal tail section, which had already been adapted for the second prototype, was further improved by adding an extension over the rear part of the fuselage. With all the improvements, an aircraft had been developed with a high degree of manoeuvrability. A total of 479 aircraft of this type were manufactured and this was the primary production aircraft of this type until the development of the Aichi D3A2 in 1942.

Aichi D3A1 on an airstrip. Source: Public Domain (unknown)

In June 1942, an improved version was developed, powered by a 1,299 hp (969 kW) Mitsubishi Kinsei 54 engine. This version was designated by the Japanese Navy as Marine Type 99 Aircraft Carrier Bomber Model 12. Some late production Model 11 aircraft already had a spinner fitted to the propeller, but this became only standard on the Model 12. The cockpit was also extended at the rear to provide the observer with better visibility and protection.^[7]

D3A2 with the extended rear of the cockpit clearly visible. Source: Public Domain (unknown)

The extra power reduced the range. To compensate for this, the internal fuel supply capacity was increased to 900 liters. With this increased fuel supply, this type became the Navy Type 99 Aircraft Carrier Bomber Model 22 in the Japanese Navy.^[8]

No fewer than 1,016 aircraft of the D3A2 were produced. As the war progressed, the Aichi D3A2 aircraft were often used as fighter aircraft. Especially when the Yokosuka D4Y replaced the Aichi D3A2 aircraft on aircraft carriers and the Aichis ended up in land-based squadrons. However, several D3A2 aircraft continued to operate on smaller aircraft carriers because the Yokosuka were too fast to allow landing on the shorter flight decks. Towards the end of the war, many D3A2 aircraft were used in kamikaze attacks.^[9][10]

By the time the war came to an end, most of the Aichi D3A1 and D3A2 aircraft had been transferred to training units. A significant number of these were equipped with dual controls and subsequently designated Aichi D3A2-K or Marine Type 99 Bomber Trainer Model 12.

Notes

1. Chant, 1999, pag. 16
2. Peattie, 2013, pag. 94
3. Francillon, 1969, pag. 24
4. Francillon, 1979, pag. 272-273
5. Peattie, 2013, pag. 94
6. Parshall, 2007, pag. 80
7. Chambers, 2018, pag. 156
8. Chambers, 2018, pag. 156
9. Francillon, 1969, pag. 24
10. Chambers, 2018, pag. 156