Nakajima B6N Tenzan Jill
The Nakajima B6N Tenzan, code-named Jill by the Allies, was the Imperial Japanese Navy's standard carrier torpedo bomber of the final years of the Second World War and the successor to the B5N. Its first flight came in 1941, but its Nakajima Mamoru engine proved unreliable and delayed service entry until 1943; the main production model, the B6N2, switched to Mitsubishi's Kasei engine, and Nakajima built 133 B6N1s and 1,133 B6N2s and B6N2as. By the time it arrived in numbers, Japan had lost most of its large carriers and its experienced aircrews, and the type fought its biggest actions from a shrinking carrier force and then from land bases.
Why It Mattered
The B6N Tenzan was the Imperial Japanese Navy's standard carrier torpedo bomber for the final years of the Second World War, built as the successor to the B5N. It arrived late: engine trouble held the programme back, and the type did not enter service until 1943, two years behind the original plan. By then the conditions it was designed for had largely vanished, as Japan had lost most of its large carriers and was desperately short of experienced pilots. The B6N nevertheless fought on through 1944 and 1945, and at Okinawa it flew both conventional bombing and kamikaze missions.
Design Notes
The Navy's 14-Shi specification called for a three-seat, low-wing, all-metal monoplane, a new carrier attack aircraft to replace the B5N. Nakajima's team, the same one that had designed the B5N, kept a similar airframe, with dihedral along the whole wing and a vertical tail that appeared to lean slightly forward. Folding outer wing panels and Fowler flaps helped the heavier aircraft work from carrier decks, though its higher landing speed still restricted it to the larger carriers. The design's gamble was power: the Navy had suggested Mitsubishi's proven Kasei engine, but Nakajima insisted on its own new Mamoru radial, citing lower fuel consumption and better growth potential. The Mamoru proved very unreliable, and the production B6N2 switched to the 1,850 hp Kasei 25 instead, in a lengthened nose. Flight testing also exposed a rolling tendency from propeller torque, cured by moving the vertical tail two degrees ten minutes to the left. A proposal to fit self-sealing fuel tanks was dropped because it would have reduced the aircraft's range by around thirty percent.
Operational History
The prototype first flew on 14 March 1941, but carrier trials did not follow until the end of 1942, aboard Ryuho and Zuikaku. Accepted for production early in 1943, the B6N1 made its combat debut that November, when fourteen aircraft attacked American shipping off Bougainville. The returning pilots claimed to have sunk three carriers and several cruisers; in fact they had attacked two large landing ships and a gunship, all of which survived, and four B6N1s were lost. At the Philippine Sea on 19 June 1944, forty-four B6Ns joined the carrier strikes against the American fleet; only fourteen survived, and none of their torpedoes struck home. With Japan's carrier force destroyed, the vast majority of later B6N2 operations took place from land bases. On 21 February 1945, three B6Ns scored a hit on the carrier Saratoga, which was never fully operational again. At Okinawa the type served as both a conventional bomber and a kamikaze aircraft, and its suicide attacks sank three destroyers and damaged the carrier Intrepid. Production ran to 133 B6N1s and 1,133 of the B6N2 and B6N2a models.
Afterlife
The B6N was retired in 1945, at the end of the war. A single complete aircraft survived: a B6N2 that the US Navy had evaluated at Patuxent River and that was valued only for scrap by 1947, when it was rescued and taken to Naval Air Station Willow Grove in Pennsylvania. The Smithsonian acquired the aircraft from Willow Grove, and it remains in the National Air and Space Museum's collection. It is the last of its kind, held in storage at the museum's Paul E. Garber facility in Suitland, Maryland, and it is currently disassembled. A land-based development, the B6N3, produced only two converted prototypes and never entered production.