Nakajima B6N Jill

Raul Colon
PO Box 29754
Rio Piedras, Puerto Rico 00929

Since the middle of the 1920s, the Japanese Imperial Navy considered carrier aircraft as its mainstay for projecting power around the Pacific Ocean. With the conversion of many uncompleted battle cruisers into fleet carriers, and the design of next generation carrier platform, Imperial Japan was able to surprise the Western Democracies, specially the United States, in not only the numbers of carriers deployed but also and more importantly, in air operations capabilities.

The centre piece of their carrier aviation arm was the torpedo bomber. Since the early days of sea-based aviation, bombing a moving seagoing vessel had always proved to be the most difficult task in the development of the aircraft as a valuable sea operational platform. Two main methods of achieving an accurate bombardment of an enemy ship were adopted by the naval carrier powers (Japan, Great Britain and America) of the times. The first was an already proven bombing method: dive bombing. Dive bombing proved very effective late in the Great War and in the inter war years, the method was perfected, especially by the German’s Luftwaffe who used that technique very successfully in their invasions of Poland, France and, eventually, the Soviet Union. But although the tactic proved somewhat successful in a sea environment, another more efficient method was needed. Thus came the advent of the aerial torpedo bombing technique.

Japan’s most successful torpedo bomber design and maybe its most recognized aircraft after the vaunted “Zeke” or Zero was the B5N Kate. Designed in 1935, the Kate entered service in the summer of 1939 and immediately assumed a primary role with the Japanese carrier aviation arm. It went on to fame during the daring Japanese attack on the American Naval Base at Pearl Harbour on the Hawaiian Islands. But with the commitment of vast aviation resources on the part of the Americans in the Pacific war effort, the B5N became outclassed by mid 1942. Nevertheless, the type still saw major operations on the Solomon and Philippines campaigns.

Since late 1939, the Japanese Navy wished to upgrade its torpedo bomber aircraft performance. Several major designs were presented by companies such as Mitsubishi and even other minor design bureaus in Japan. None of them passed the Navy’s rigorous pre-design development evaluation phase. But as was the case with the B5, the Nakajima Corporation came to the aid of the Navy with the unveiling of its new torpedo bomber design, the B6N Tenzan or Heavenly Mountain and codenamed by the Allies as the Jill. The Jill was an all metal design aircraft. It had an airframe length of 35’-8” with 12’-5.5” in height. Wingspan was 48’-10” with a total wing area covering 400.43sq ft. The complete frame weight it at 6,636lb while empty and the aircraft could take-off with a maximum weight of 12,456lb. Initially, the Jill was to be fitted with a Mitsubishi Kasei radial engine, but after testing, it was determined that a better performance engine could improve aircraft manoeuvring capabilities, thus the original engine was replaced by the new Nakajima Mamoru radial engine.


The Mamoru gave the plane such an increase in power and torque that the frame was not able to compensate for it, thus causing major stability difficulties even on level flight. After a series of accidents, the Japanese Navy ordered Nakajima to replace the power plant and install the original Kasei engine. The Kasei proved capable of providing the aircraft with maximum speeds of 299mph. It would also offer the B6N a climb rate of 16,404ft in ten minutes and twenty four seconds. The operational ceiling for the bomber was just short of 30,000ft. The newly installed engine also provided the aircraft with the ability to operate 1,085 miles away from its base carrier. A crew of three; a pilot, radioman and navigator, and the bombardier; operated the bomber. The Jill was protected from the expected Allied fighter attack by a trainable 13mm Type II machine gun mounted in the rear of the cockpit and a .303mm machine gun Type 97 fitted in a ventral tunnel position. The Tenzan carried a bomb weight of 1,754lb, mainly a torpedo, but in some instances, the aircraft was fitted with free-fall bombs for attacking land targets. Some 133 examples of the original Jill concept were produced and it entered front line service with the Imperial Navy in March 1944.

The Jill was eventually deployed in all of Japan’s fleet carriers as well as in some escort carriers squadrons. They first saw extended action during the Philippine Sea campaign in June 1944 and sustained enormous losses. Most of the B6Ns lost during the battle were due to the fact that by this time the Allies were able to field more advanced aircraft and possessed superior numbers of them. In mid July of that year, Nakajima began production of the B6N-2, a slightly modified Jill. By the end of the war, the B6N-2 production topped at 1,133 samples. The Jill never got time to prove itself in the skies of the vast Pacific. The loss of the Philippines marked the end of major carrier operations by the once vaunted Japanese Navy and the role of the Jill switched from carrier based action to land base operations where many of the remained examples were modified to be used by fanatical Japanese pilots in suicide or kamikaze missions. A few examples, an estimated forty units, survived the war. Some of them were collected by the Allies for intelligence gathering and analysis, while the rest were destroyed in aircraft graveyards.

 ENGINE 1 x Mitsubishi MK4T "Kasei-25",1380
    Take-off weight 5650 kg 12456 lb
    Empty weight 3010 kg 6636 lb
    Wingspan 14.9 m 48 ft 11 in
    Length 10.87 m 35 ft 8 in
    Height 3.8 m 12 ft 6 in
    Wing area 37.2 m2 400.42 sq ft
    Max. speed 480 km/h 298 mph
    Ceiling 9040 m 29650 ft
    Range w/max.fuel 3045 km 1892 miles
 ARMAMENT 2 x 7.7mm machine-guns, 800kg of bombs


Aircraft Carriers, Chris Bishop & Chris Chant, Amber Books 2004
Jane’s Recognition Guide, Gunter Endres & Mike Gething, HarperCollis 2002
Japan’s Secret Bombers: 1919 – 1945, John Glasston, TouchTone, 1982