The Nakajima B5N (Allied reporting name: Kate) was the Imperial Japanese Navy's standard torpedo bomber for the first years of World War II. While the B5N was substantially faster and more capable than its Allied counterparts, the TBD Devastator and Fairey Swordfish, it was close to obsolescence by the time of the Pearl Harbor Attack. Nevertheless, the B5N operated throughout the whole war. Although primarily used as a carrier-based aircraft, it was also used as a land-based bomber on occasions. The B5N had a crew of 3: pilot, navigator/bombardier/observer, and radio operator/gunner.
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 fuel tanks. Keen to maintain the high performance of the type, the Navy was reluctant to add weight in the form of armour, and instead looked to obtaining a faster version of the aircraft in the hopes of out-running 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 unremedied, this version replaced the B5N1 in production and service from 1939. It was this version that would be used by the Navy in the attack on Pearl Harbor. Apart from this raid, the greatest successes of the B5N2 were the key roles they played in sinking the US Navy aircraft carriers Yorktown, Lexington and Hornet.  
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