Nakajima B5N Kate


Shortly after the announcement of the 9 Shi’s design objectives, Nakajima’s engineers Takao Yoshoda and Yasuo Fukuda projected the new aircraft. It was given the factory designation “Q”, and later the military designation “9 Shi Experimental Torpedo-Bomber” (B4N1). It was a classic fixed-undercarriage biplane with a mixed construction.
The work was delayed, and two prototypes were completed only in 1936. The first one was powered by the Nakajima Hikari 1 engine, and the second used the Nakajima Kotobuki 3 power unit. However, none of the above-mentioned planes met the assumed requirements and was not approved by the Imperial Navy.
The situation of the deck aviation, as in the case of the 7 Shi requirements, forced the mass production of the B4Y1 (developed in Kugisho). It was considered the best option, although it did not meet all the expectations.
At the Aviation Arsenal in Yokosuka, a team of designers working on the development of a new torpedo-bomber was headed by Eng. Sanae Kawasaki. The design of the machine, which was given the designation “9 Shi Experimental Torpedo-Bomber” (B4Y1), made it possible to install various types of engines. In order to make the construction pace as fast as possible, generally available materials and components were used during the construction. For this purpose, a new fuselage structure was developed, and its tail and wings were adapted from the Kawanishi E7K1 reconnaissance seaplane. The plane had a mixed structure and a fixed landing gear. The pilot’s cabin was uncovered, and the remaining cabins were covered with a common, richly glazed canopy. The first prototype, which was completed and flown in 1935, was powered by a 620 hp Hiro Type 91-I V-engine. Four more prototypes were built over the course of the following year. They had an increased wingspan and new power units. The second and third prototypes were powered by Nakajima Kotobuki 3 engine with a take-off power of 640 hp. Fourth and fifth prototype received Nakajima Hikari 2 radial engine with a take-off power of 840 hp. The tests showed that the last two prototypes had the best performance, and they were just selected for the comparative tests with the B4M1 and B4N1. In November 1936, Kaigun Koku Hombu officially accepted the B4Y1 prototype into series production, giving it the designation “Type 96 Torpedo-Bomber”. As with the B3Y1, the production of the new machine was split between Nakajima, Mitsubishi, and the Hiro Naval Aviation Arsenal (Kaigun Kokusho). Production was discontinued in 1938. A total of 205 copies were built.
Until 1940, the B4Y1 aircraft operated from the “Akagi”, “Kaga”, “Sōryū” and “Ryūjō” carriers, actively participating in the second Japanese Chinese conflict. They were not very modern and significantly differed in performance from the Mitsubishi A5M deck fighters. That is why the cooperation of the individual airborne units was very difficult. After the outbreak of the Pacific War, the B4Y1 planes were already moved to second line and training units. Only the oldest Japanese carrier, “Hōshō”, still had eight machines of this type, but after commencing combat operations, it was rearmed with Nakajima B5N2 torpedo-bombers. In the Allied code, B4Y1 received the designation Jean.

kate zd3

Birth of B5N
In 1936, the obsolete and “emergency” torpedo-bombers were replaced with newer B4Y1s, but this was a temporary solution. The new plane had a top speed of 277 km/h and a range of 1,574 km, which was enough at that time, but it could not be enough in future. In 1935, the monoplane fighter, later known as the Mitsubishi A5M Claude, made its first flights, reaching a speed of 449 km/h at an altitude of 3,000 m and proving that the era of biplanes came to an end.
In 1935, Kaigun Koku Hombu released the technical order of the 10 Shi containing radically new requirements resulting from a completely new approach to the subject of a deck torpedo-bomber. The given characteristics were much higher than any aircraft of this type developed so far. The set task was very ambitious, but both Mitsubishi and Nakajima decided to try their hand at this competition.
The 10 Shi requirements expected that the new airplane should reach a maximum speed of not less than 330 km/h and have an overall performance impossible to achieve by a biplane. During the tests of the A5M Claude there were problems with deviations from the course in the last stages of the landing approach, which could be very dangerous for the aircraft landing on the carrier, but it was found that the problem could be solved by the use of flaps, which at that time were considered as novelty, although in their early form they were already used during the World War I.
A great help for the constructors was getting acquainted with the Northrop Gamma 5A plane. Its only prototype (registration number X 14997) was purchased in order to learn about new technologies. On October 29, 1935, it was sent from USA to Japan. The machine was handed over to the Navy, where it was given the designation BXN1. During the tests, the plane was crashed and completely destroyed, but before it happened, a lot of valuable information was collected.