The situation of the Japanese Armed Forces on the next day after the First World War was rather confusing regarding the conditions of the armies with which the country had aligned itself during the conflict. The Navy clearly stood out due to the quality of the ships and the training of the crews. The Army, regardless of being imbued with the well known combative spirit of Japanese soldiers, was almost fully equipped with materials acquired from other nations, especially the most modern ones, a factor which certainly had not benefited the development of a specialized national industry, and which tied the country to the will of the nations which supplied the weapons. Regarding the aviation there was only an embryo, divided between the Navy and the Army, and constituted exclusively by imported aircraft. This was not due to a lack of interest towards the new weapon, but to the lack of experience and technological knowledge which Japan, enclosed during centuries on its feudal condition, had no chance of acquiring. The few aeronautical companies which already existed sent their engineers to acquire specialized knowledge in the universities and industries of western countries. When they returned, around 1930, the first constructional experiments were started and, about five years later, the first results of this effort of renovation were finally seen. The history of the Second World War would show that these results would be greatly superior to the most optimistic expectations, especially considering that they were obtained by an industry which was created hurriedly and from scratch. After three years the Japanese Armed Forces would receive the aircraft which would constitute the backbone of their respective aviations, and which would give the Allies a lot to do. In 1937 the Nakajima B5N (later denominated "Kate" by the Americans), the aircraft which would sink so many American aircraft carriers and which would be the backbone of the torpedo bomber units, effectuated its first flight. In 1938 the Aichi D3A ("Val"), the best Japanese dive bomber of the conflict, flew for the first time and in 1939 it was the turn of the Mitsubishi A6M ("Zero"), the fighter aircraft which needs no presentation. When in 1937 the Kate, which had been designed in 1935 by the research group led by engineer Katsuji Nakamura, from the Nakajima Hikoki K. K., effectuated its test flight it widely surpassed the qualities requested in the specification presented by the Navy for a naval torpedo bomber and, after some small modifications were made to it, was immediately accepted. It was a low-wing monoplane single-engine aircraft, of entirely metallic construction and fitted with a retractable landing gear. Its foldable wings allowed to accommodate it in the hangar of the aircraft carriers. It was a polyvalent aircraft, for it could operate as a dive bomber as well. The engine, initially a Nakajima Hikari 3 of 770 horsepower, would soon be replaced by a Nakajima Sakae 11 of 1000 horsepower, which would grant to the aircraft a modest increase of its speed as well as an increase of its safety factor. During its production cycle, 1149 exemplars left the production lines. From the late 1943 onwards the BN5 would be replaced by the B6N, aircraft of better characteristics, but it would continue operating mainly as an anti-submarine aircraft, carrying the first Japanese airborne radars in the late 1944, before being relegated to training service. On the other hand, it seems that some exemplars of the Kate took part in suicide attacks.