Before the advent of the B5N, Japan used the B2M and B4Y as torpedo biplanes. However, the significant limitations of biplanes were obvious, so in 1935, inspired by the monoplane A5M fighter, the Imperial Japanese Navy developed the 10-Shi torpedo bomber specification.
Nakajima and Mitsubishi participated in the competition. Nakajima decided to incorporate many new ideas in their B5N design. The prototype had a hydraulic wing-folding system so that the plane could be stored on an aircraft carrier, and Fowler flaps were used to improve stability while landing. In addition, the B5N had a hydraulic retractable landing gear system.
Although Mitsubishi also received an order for production of its own B5M torpedo bomber, the Nakajima model won the contest and in 1937 was accepted as a production model carrier-based torpedo bomber.
To create a production model, however, some changes had to be made in the prototype’s design. The wing-folding system was changed to a manual one, and the flaps were replaced with conventional ones.
In 1939, the B5N2 was developed. It differed from its predecessor in its more powerful and reliable Sakae engine, which produced 1000 hp instead of the Hikari 3’s 770.
At the beginning of World War II, the B5N torpedo series had no worthy competitors among Allied aircraft and made a great showing in the attack on Pearl Harbor, as well as in subsequent operations, where B5N forces sank four U.S. aircraft carriers within one year.
A total of 5,928 B5Ns were built.