The engines of choice became the in-house Nakajima Homare 21 series 18-cylinder air-cooled radial offering up to 1,990 horsepower output each. Radials required air cooling and larger engine nacelles but were less delicate than their inline brethren. The pilot's location in the design offered clear vision to each engine installation while still keeping forward vision rather excellent for carrier deck approaches and take-offs.
Satisfied with the Nakajima offering, the IJN ordered full development of the aircraft and contracted for six prototypes to prove the design sound. Engineers fought consistently against weight gains being incurred from the specified armament fit as well as cockpit, systems and fuel stores armoring. With the ballooning weight, the aircraft was further hampered by the less-than-desired output of the engine pair and handling was deemed unsatisfactory to boot. A gun-less prototype went to the air for the first time on July 13th, 1944 and managed only 371 miles per hour as its top speed.
This led to a period of hasty refinement for the design until it was realized that a full reworking was in order to truly meet the IJN demand. Six aircraft were ultimately completed - two interestingly finalized as two-seaters - but four of the stock were eventually lost to various accidents, proving that the J5N needed much more work than time allowed. The constraints of a failing war effort and the changing fortunes of Japan in the Pacific ultimately led to project cancellation in February of 1945. The unconditional Japanese surrender then arrived in August officially ending World War 2 in full.
The J5N was to carry the name "Tenrai" in service, this translating to "Heavenly Thunder".
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