The Yokosuka B4Y, (Navy Type 96 Carrier Attack Bomber), carrier-borne

torpedo bomber A torpedo bomber is a military aircraft designed primarily to attack ships with aerial torpedoes. Torpedo bombers came into existence just before the First World War almost as soon as aircraft were built that were capable of carrying the weight ...

was used by the Imperial Japanese Navy Air Service from 1936 to 1943. The B4Y replaced the Mitsubishi B2M2 and was the last

biplane A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While ...

bomber A bomber is a military combat aircraft designed to attack ground and naval targets by dropping air-to-ground weaponry (such as bombs), launching aerial torpedo, torpedoes, or deploying air-launched cruise missiles. The first use of bombs dropped ...

used operationally by the

Imperial Japanese Navy The Imperial Japanese Navy (IJN; Kyūjitai: Shinjitai: ' 'Navy of the Greater Japanese Empire', or ''Nippon Kaigun'', 'Japanese Navy') was the navy of the Empire of Japan from 1868 to 1945, when it was dissolved following Japan's surrender ...

. The Allied reporting name was "Jean".

Design and development

In 1932, the

issued a requirement for a new carrier-borne attack aircraft.

Aichi is a prefecture of Japan located in the Chūbu region of Honshū. Aichi Prefecture has a population of 7,552,873 () and a geographic area of with a population density of . Aichi Prefecture borders Mie Prefecture to the west, Gifu Prefectu ...

Mitsubishi The is a group of autonomous Japanese multinational companies in a variety of industries. Founded by Yatarō Iwasaki in 1870, the Mitsubishi Group historically descended from the Mitsubishi zaibatsu, a unified company which existed from 1870 ...

and Nakajima responded to this requirement and each built a

prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and Software prototyping, software programming. A prototyp ...

. None of these aircraft were deemed satisfactory, and the service thus issued in 1934 a new requirement, 9-''Shi'', for a more capable aircraft to replace the obsolescent

Yokosuka B3Y The Kugisho B3Y, or Navy Type 92 Carrier Attack Bomber, also popularly titled Yokosuka B3Y, was a Japanese aircraft carrier, carrier-based torpedo bomber of the 1930s. It was designed by the Naval Air Technical Arsenal at Yokosuka, and while unim ...

The B4Y was designed by

Sanae Kawasaki SANAE is the South African National Antarctic Expedition. The name refers both to the overwintering bases (numbered in Roman numerals, e.g. SANAE IV), and the team spending the winter (numbered in Arabic numerals, e.g. SANAE 47). The current bas ...

at the First Naval Air Technical Arsenal at Yokosuka. Regarded only as an interim type, the Navy wanted a

offering performance comparable to the

Mitsubishi A5M The Mitsubishi A5M, formal Japanese Navy designation , experimental Navy designation Mitsubishi Navy Experimental 9-''Shi'' Carrier Fighter, company designation Mitsubishi ''Ka''-14, was a Japanese carrier-based fighter aircraft. It was the worl ...

monoplane A monoplane is a fixed-wing aircraft configuration with a single mainplane, in contrast to a biplane or other types of multiplanes, which have multiple planes. A monoplane has inherently the highest efficiency and lowest drag of any wing confi ...

fighter. The result was a biplane with fixed

landing gear Landing gear is the undercarriage of an aircraft or spacecraft that is used for takeoff or landing. For aircraft it is generally needed for both. It was also formerly called ''alighting gear'' by some manufacturers, such as the Glenn L. Martin ...

and an all-metal structure with metal or fabric skin. To speed development and production, the B4Y utilised the wings from the

Kawanishi E7K The Kawanishi E7K was a Japanese three-seat reconnaissance seaplane mainly in use during the 1930s. It was allocated the reporting name Alf by the Allies of World War II. Design and development In 1932 the Imperial Japanese Navy requested the K ...

. The B4Y1 was also the first Navy carrier attack aircraft to utilize an air-cooled engine, as the prototype that was equipped with the

Nakajima Hikari The Nakajima Hikari (Japanese: 光 "Light") was a nine-cylinder, air-cooled, radial aircraft engine developed in Japan for Navy use during World War II by the Nakajima Aircraft Company. It was a development of the Nakajima Kotobuki and Wright ...

2 radial engine performed better than its competitors. The crew of three occupied two

cockpit A cockpit or flight deck is the area, usually near the front of an aircraft or spacecraft, from which a Pilot in command, pilot controls the aircraft. The cockpit of an aircraft contains flight instruments on an instrument panel, and the ...

s. The pilot in the open front cockpit and the other two crewmen, (navigator and radio operator/gunner), in the enclosed rear cockpit.

Operational Service

On 12 December 1937 3 B4Y1s were involved in the

Panay incident The USS ''Panay'' incident on December 12, 1937, was a Japanese bombing attack on the U.S. Navy river gunboat and three Standard Oil Company tankers on the Yangtze River. They strafed survivors in the water. The boats were rescuing U.S. and ...

during a Japanese attack on the

United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

gunboat A gunboat is a naval watercraft designed for the express purpose of carrying one or more guns to bombard coastal targets, as opposed to those military craft designed for naval warfare, or for ferrying troops or supplies. History Pre-steam ...

Panay Panay is the sixth-largest and fourth-most populous island in the Philippines, with a total land area of and has a total population of 4,542,926 as of 2020 census. Panay comprises 4.4 percent of the entire population of the country. The City o ...

'' while she was anchored in the

Yangtze River The Yangtze or Yangzi ( or ; ) is the longest list of rivers of Asia, river in Asia, the list of rivers by length, third-longest in the world, and the longest in the world to flow entirely within one country. It rises at Jari Hill in th ...

outside of

Nanjing Nanjing (; , Mandarin pronunciation: ), alternately romanized as Nanking, is the capital of Jiangsu province of the People's Republic of China. It is a sub-provincial city, a megacity, and the second largest city in the East China region. T ...

. Although primarily used as a carrier-based aircraft, the B4Y1 was also used as a land-based

on occasion. In 1940, the

Nakajima B5N The Nakajima B5N ( ja, 中島 B5N, Allied reporting name "Kate") was the standard carrier-based torpedo bomber of the Imperial Japanese Navy (IJN) for much of World War II. Although the B5N was substantially faster and more capable than its Al ...

replaced the B4Y1 as the primary carrier attack aircraft, though the B4Y1 did remain in service as an advanced trainer, and flew from and until 1943. Before its replacement, the B4Y1 had flown during the

Second Sino-Japanese War The Second Sino-Japanese War (1937–1945) or War of Resistance (Chinese term) was a military conflict that was primarily waged between the Republic of China and the Empire of Japan. The war made up the Chinese theater of the wider Pacific Th ...

and served at the

Battle of Midway The Battle of Midway was a major naval battle in the Pacific Theater of World War II that took place on 4–7 June 1942, six months after Japan's attack on Pearl Harbor and one month after the Battle of the Coral Sea. The U.S. Navy under ...

during June 1942, where eight of them were operated from ''Hōshō''. It was one of these planes from ''Hōshō'' which took photographs of the burning on 5 June 1942.

Variants

;First Prototype:

Hiro Type 91 520 hp water-cooled W-12 The Hiro Type 91, (full designation Hiro Type 91 520 hp water-cooled W-12), was a 12-cylinder, water-cooled, W engine developed for aircraft use by the Imperial Japanese Navy in the mid-1930s. Power was in the 450 kW (600 hp) ran ...

driving a two-bladed propeller. ;Second and Third Prototypes: Nakajima Kotobuki 3 nine-cylinder air-cooled radial driving a two-bladed propeller. ;Fourth and Fifth Prototype and Production Aircraft:

Nakajima Hikari 2 The Nakajima Hikari (Japanese: 光 "Light") was a nine-cylinder, air-cooled, radial aircraft engine developed in Japan for Navy use during World War II by the Nakajima Aircraft Company. It was a development of the Nakajima Kotobuki and Wright ...

nine-cylinder air-cooled radial driving a two-bladed propeller.

Production

* First Naval Air Technical Arsenal, Yokosuka: 5 prototypes (1935–36) *

Nakajima Aircraft Company The was a prominent Japanese aircraft manufacturer and aviation engine manufacturer throughout World War II. It continues as the car and aircraft manufacturer Subaru. History The Nakajima Aircraft company was Japan's first aircraft manufactur ...

: 37 production aircraft (1937–38) *

Mitsubishi Heavy Industries is a Japanese multinational engineering, electrical equipment and electronics corporation headquartered in Tokyo, Japan. MHI is one of the core companies of the Mitsubishi Group and its automobile division is the predecessor of Mitsubishi Mo ...

, Nagoya: 135 production aircraft (1937–38) * 11th Naval Air Arsenal, Hiro: 28 production aircraft (1938) * Total: 205 aircraft

Operators

; * Imperial Japanese Navy Air Service The B4Y1 was operated from the aircraft carriers , , , , , and ''Unyō'', as well as the 13th and 15th

Kōkūtai A ''Kōkūtai'' () was a term used by the Imperial Japanese Navy Air Service (IJNAS) to designate a military aviation unit, similar to the Air Groups in other air arms and services of the time. (''Group'' in the British Royal Air Force, ''Grupp ...

(Air Groups).

Specifications (B4Y1)

References

;Notes ;Bibliography * * ''English Translation of Kojinsha No. 6 Warships of the Imperial Japanese Navy.'' * {{Allied reporting names B4Y B4Y, Yokosuka Single-engined tractor aircraft Biplanes Carrier-based aircraft Aircraft first flown in 1935