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Yokosuka B3Y / Kugisho B3Y

The Kugisho B3Y, also known as the Navy Type 92 Carrier Attack Bomber or the Yokosuka B3Y, was a torpedo bomber utilized by the Imperial Japanese Navy during the 1930s.

The aircraft was developed by the Naval Air Technical Arsenal located in Yokosuka, Japan.

Despite its lackluster performance during testing, the Imperial Japanese Navy commissioned the aircraft for service until it was eventually replaced by more advanced models.

In 1932, the Imperial Japanese Navy initiated the 7-Shi requirement for a new torpedo bomber to replace the Mitsubishi B2M.

The Yokosuka air arsenal developed its own design to meet this requirement, competing against designs by Mitsubishi and Nakajima.

The resulting aircraft was a single-engine biplane with a steel tube fuselage and two-bay wooden wings that could fold rearwards for storage aboard aircraft carriers.

It was equipped with a single Hiro Type 91 W engine rated at 450 kW (600 hp) and had a seating capacity of three.

During testing, the aircraft exhibited poor stability and control, and the engine was deemed unreliable. However, the competing Mitsubishi and Nakajima designs were even less successful.

After modifications were made by Tokuichiro Gomei of Aichi Kokuki, the aircraft was accepted by the Navy in August 1933 as the Kugisho Navy Type 92 Carrier Attack Bomber, with a short designation of B3Y1. Production was carried out by Aichi, Watanabe, and the Hiro Naval Arsenal, with a total of 129 units produced by 1936.

Despite its operational use in the early stages of the Second Sino-Japanese War, the B3Y1 was plagued by engine problems that frequently grounded the aircraft.

Nevertheless, it gained a reputation for accurate level bombing against small targets.

The Yokosuka B3Y was gradually phased out of operational service and replaced by Aichi’s D1A dive bomber and Yokosuka’s B4Y torpedo bomber.





9.5 m (31 ft 2 in)


13.51 m (44 ft 4 in)


3.73 m (12 ft 3 in)

Wing area

50 m2 (540 sq ft)

Empty weight

1,850 kg (4,079 lb)

Gross weight

3,200 kg (7,055 lb)


1 × Hiro Type 91 520 hp water-cooled W-12,

W-12 water-cooled piston engine,

450 kW (600 hp)


2-bladed fixed-pitch propeller


Maximum speed

219 km/h (136 mph, 118 kn)


4 hours 30 minutes

Wing loading

64 kg/m2 (13 lb/sq ft)


0.14 kW/kg (0.085 hp/lb)



1× fixed, forward-firing 7.7 mm (.303 in) machine gun &

1× flexible, rearward-firing machine gun in observer’s cockpit


1× 800 kg (1,764 lb) torpedo


500 kg (1,102 lb) bombs.

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.


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