Nakajima B5N

At the beginning of the Second World War, the Nakajima B5N was the most important Japanese torpedo bomber. Production of this aircraft would continue until 1943 and was operational until 1944 when gradually replaced by the Nakajima B6N. Until then, the aircraft had played a crucial role in most of the Imperial Japanese Navy's operations, such as the attack on Pearl Harbor.

Nakajima B5N1, TA-320, Tateyama Kokutai. Source: Wilco Vermeer collection

The "Kate", as the Allies called the Nakajima B5N, was the standard carrier-based torpedo bomber of the Imperial Japanese Navy (IJN). The aircraft played a major role during the Second World War, until it was replaced in 1944 by its successor, the Nakajima B6N "Tenzan". In 1932, specifications were issued for a new torpedo bomber to which three companies, Aichi, Mitsubishi and Nakajima, responded by each building a prototype. However, none of these would receive the blessing of the Japanese navy and they opted for their own design, the Yokosuka B4Y, as a temporary solution.^[1]

Still, the IJN was eagerly looking for an aircraft whose performance would be close to that of the new Mitsubishi A5M fighter. Therefore, new specifications were issued again in 1935. These entailed a three-seater attack aircraft with folding wings, able to carry a bomb load of 800 kg and powered by either a Nakajima Hikari or a Mitsubishi Kinsei engine. The Nakajima team, led by Katsuji Nakamura, responded with the design of the Nakajima type K.^[2][3]

This was an all-metal monoplane with retractable landing gear and hydraulically folding wings. The prototype flew as early as January 1937 and was powered by a Nakajima Hikari 2 engine. Partly because of the hydraulic system, the IJN was somewhat reluctant about the aircraft. It was thought too advanced and it was feared this would lead to maintenance problems. For the time being, it was therefore decided to further develop the Mitsubishi design, the B5M, as an interim type. However, Nakajima made the necessary improvements and replaced the hydraulic system with a manual one. The second prototype was also fitted with the newer 840 hp Hikari 3 engine and proved superior to the Mitsubishi design.^[4]

This version was put into production as the Nakajima B5N or Type 97 Flight Deck Attack Bomber. The first production series, designated Nakajima B5N1, was operationally deployed during the 2nd Sino-Japanese War and revealed several problems. These were mainly due to poor protection for the crew and fuel tanks, a common problem with Japanese military aircraft of that time. With the production of the Nakajima B5N2, an attempt was made to 'disguise' these issues by means of a more powerful engine and thus more speed.^[5][6]

The new aircraft was put into production and incorporated into the Imperial Japanese Navy as the Navy Type 97 Aircraft Deck Attack Bomber Model 1 (later known as Model 11). The B5N1 was soon fully deployed by the IJN, stationed both on land and on board the aircraft carriers. It undertook its first war actions during the Second Japanese-Chinese War in 1939. Due to the absence of armour and self-sealing fuel tanks (a problem with almost all Japanese aircraft), it achieved only mediocre success.

B5N1, 9-348, 14 Kokutai. Source: Wilco Vermeer collection

The B5N1 would soon be replaced by a new version. The B5N1 aircraft were withdrawn from the front line and converted into the Nakajima B5N1-K trainer version.

The next version was equipped with the more powerful Nakajima NK1B Sakae 11 engine in December 1939. Because this engine had a narrower design, the nose of the aircraft also became slimmer which significantly enhanced the pilot’s view. Although performance did not increase much, the improved reliability of the engine quickly made the B5N2 the replacement for the B5N1 as the Navy Type 97 Aircraft Attack Bomber Model 12.

When Japan launched its attack in December 1941, the B5N2 had already completely replaced its predecessor. Production of the aircraft ended in 1943. By then, a total of 1,149 B5N1 and B5N2 aircraft had been built. Nakajima had produced a total of 669 of both versions between 1936 and 1941. Aichi and the 11th Marine Depot accounted for 200 and 280 B5N2 aircraft respectively.

B5N2, Yo-335, Yokosuka Kokutai. Source: Wilco Vermeer collection

Until 1944, the aircraft was Japan's main torpedo bomber and high-level bomber aboard its aircraft carriers. After this it was gradually replaced by the Nakajima B6N. Until then, the "Kate" had played a major role in Pearl Harbor and the sinking of the aircraft carriers USS Lexington (CV-2), USS Yorktown (CV-5) and USS Hornet (CV-8), among others.^[7]

Notes

1. Chambers, 2017, pag. 8
2. Francillon, 1979, pag. 412-413
3. Chambers, 2017, pag. 9
4. Chambers, 2017, pag. 9
5. Francillon, 1979, pag. 412-413
6. Chambers, 2017, pag. 9-10
7. Chambers, 2017, pag. 6