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. Combat experiences during the Second Sino-Japanese War 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 - Nakajima's own Sakae Model 11, 14-cylinder twin-row radial, as used in the initial models of the Mitsubishi A6Mfighter – 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.
Equipment
The navigator/bombardier/observer position was equipped with a Type 90bombsight, which was a long vertical tube located in the front-left of the seat. There was also a Type 3reflectorcompass for precise navigation that was mounted on the top of the cockpit frame. The radio-operator/gunner position was equipped with one of the standard issue radio sets that was mounted in front of the radio-operator/gunner's seat and behind the navigator/bombardier/observer's seat. The radio-operator/gunner also operated one flexible 7.7 mm Type 92 machine gun at the rear end of the cockpit. One Type 91 torpedo could be mounted on the racks that were fixed eccentrically to the right at the bottom of fuselage. Alternatively, racks could be replaced to carry either one 800 kg bomb or two 250 kg bombs or six 60 kg bombs. Replacing the racks and exchanging between the torpedo and bombs was not a trivial process and could take more than two hours to complete.
Operational history
While B5N was primarily employed as a carrier-based aircraft, it was also occasionally used as a land-based bomber. It carried a crew of three: pilot, navigator/bombardier/observer, and radio-operator/gunner. Like with other IJN multi-seat aircraft, an individual bomber was commanded by the senior ranking crew member aboard, which could be the observer rather than the pilot. The initial model B5N1 first saw action in the Second Sino-Japanese War. The updated model B5N2 later played a major role in the Attack on Pearl Harbor. One of B5N2's carried Mitsuo Fuchida, the commander of the attack, with one from the carrier credited with sinking the battleship. Five torpedo bombers were shot down in the first wave. Apart from this raid, the greatest successes of the B5N2 were the key roles it played in sinking the United States Navyaircraft carrier at the Battle of the Coral Sea and at the Battle of the Santa Cruz Islands, and the disabling of the at the Battle of Midway, which led to its sinking by the. B5N2 torpedo bombers normally performed a coordinated attack on enemy carriers together with Aichi D3A dive bombers. Ideally, dive bombers would help to suppress the ship's anti-aircraft fire, which improved the chances of success for low and slow flying torpedo bombers. During the Battle of the Eastern Solomons, IJN tried to minimize losses to torpedo bombers and initially sent only the dive bombers to attack and cripple US carriers for the subsequent torpedo strike. However, this proved to be unsuccessful tactic, since torpedo bombers did not even get a chance to launch before the battle was over. 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.
None of the 1,150 production B5Ns survived World War II intact. Only two partially-recovered B5Ns are known to exist, neither of them airworthy. Replicas of the B5N2s were made using stretched fuselages from U.S. North American T-6 Texan trainers, 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. A B5N was unveiled at the Pacific Aviation Museum in Honolulu, Hawaii on 18 April 2016.
