Although the B5N was substantially faster and more capable than its Allied counterparts, the TBD Devastator, Fairey Swordfish and Fairey Albacore, it was nearing obsolescence by 1941. Nevertheless, the B5N operated throughout the whole war, due to the delayed development of its successor, the B6N. In the early part of the Pacific War, flown by well-trained IJN aircrews and as part of well-coordinated attacks, the B5N achieved particular successes at the battles of Pearl Harbor, Coral Sea, Midway, and Santa Cruz Islands.
Primarily a carrier-based aircraft, it was also occasionally used as a land-based bomber. The B5N carried a crew of three: pilot, navigator/bombardier/observer, and radio operator/gunner.
The B5N was designed by a team led by Katsuji Nakamura in response to a 1935 specification by the Navy for a torpedo bomber to replace the Yokosuka B4Y. Internally designated Type K by Nakajima, it successfully competed with the Mitsubishi B5M for a production contract. The first prototype flew in January 1937 and was ordered into production soon afterwards with the full designation Type 97 Carrier Attack Bomber (kyū-nana-shiki kanjō kōgeki-ki or kankō for short  九七式艦上攻撃機).
Nakajima B5N1 "Kate" torpedo bomber taking off from the aircraft carrier Akagi
The B5N soon saw combat, first in the Sino-Japanese War, where combat experience revealed several weaknesses in the original B5N1 production model. These were mainly concerned with the lack of protection that the design offered its crew and its fuel tanks. Keen to maintain the high performance of the type, the Navy was reluctant to add weight in the form of armor, and instead looked to obtaining a faster version of the aircraft in the hopes of outrunning enemy fighters. The B5N2 was given a much more powerful engine, and various modifications were made to streamline it. Although its performance was only marginally better, and its weaknesses remained un-remedied, this version replaced the B5N1 in production and service from 1939.
The B5N served as the basis for a follow-on design, the B6N, which eventually replaced it in front line service. The B5N continued to fly in secondary roles, such as training, target towing, and anti-submarine warfare. Some of the aircraft used for this latter purpose were equipped with early radars and magnetic anomaly detectors. B5Ns were also used as bombers during the unsuccessful defence of the Philippines in October 1944, suffering severe losses. Later in the war, they were also used for kamikaze attacks.
Altogether, around 1,150 were built; however, not a single complete example survived. Replicas of the B5N2s were made from U.S. North American T-6 Texan trainers, and Aichi D3A dive bombers were created using BT-13 Valiant training aircraft, which were modified to represent Japanese aircraft for the movie Tora! Tora! Tora!, and have been used in a number of movies and airshows since to depict the aircraft.
One recovered B5N2 is at the Wings museum in Balcombe, West Sussex, UK; This large portion was recovered from the Kuril Islands by a British private collector in 2003.
Guns: 1 × 7.7 mm Type 92 machine gun 'Ru' (Lewis) in rear dorsal position, fed by hand loaded drum magazines of 97 rounds. A number of B5N1s were equipped with 2 × 7.7 Type 97 machine guns in the wings.
Bombs: 1 × 800 kg (1,760 lb) type 91 torpedo or 1x 800kg (1,760lb) bomb or 2 × 250 kg (550 lb) bombs or 6 × 132 kg (293 lb) bombs