Japanese Aircraft Online Model Contest 013

Sunday, 10 November 2019

CINCPAC - CINCPOA Translations - Nakajima B6N "Tenzan" (Jill), 131 Kokutai pt.2

Part #2


The following data concerning speeds and ranges are based both on what POW had experienced and on what he had read. His experience was not great and the information should be evaluated accordingly.

At economical speed of about 130 knots IAS at 200 meter altitude carrying torpedo, about 900-1,000 miles. This was based on 1,550 liter fuel load, war condition, using 87 octane gas, figuring a fuel consumption of about 180 liters per hour. It vas POW's opinion that figures given in JAPANESE AIRCRAFT, Performance and Characteristics, TAIC Manual No. 1 were too high. Figures on which POW based his opinion are all his estimates.

Effective Radius
POW was informed at KUSHIRA that allowing tine for run-in, launching, evasive tactics, etc. in the battle area, the distance from KUSHIRA airfield to southern OKINAWA would leave little gas in the tanks on his return. This flight was to be made with 87 octane gas, war condition (torpedo), speed (IAS) en route about 125-130 knots, altitude about 150 meters.

Range in Recce Condition
Estimated about 1,600 miles at economical speed, 87 octane, but POW was unable to recall clearly.

At about 5,000 meters, maximum speed level flight without torpedo using 87 octane gas and cutting the supercharger and water-methanol, about 260 knots. POW said his fastest level flight at 1,000 meters in recce codnition with 87 octane gas cutting in supercharger and water methanol was about 230 knots by his instruments. He said, however, that he held this speed only an instant, but thought that he could have run it up to about 250 knots had he continued to gun the plane.
With torpedo war-load and 87 octane gas, level flight, maximum speed cutting in supercharger and water-methanol was estimated at about 200 knots IAS, altitude unverifiable. POW observed that in his opinion TAIC figures in above mentioned manual were too high.
POW's plane was new; it had about 60 hours flying time when he took it into action.

About 9,000 meters, recce condition, 87 octane.

Top gun (flexible) 1 x 7.9 mm; bottom gun (flexible) 1 x 7.9 mm; no forward firing guns. Fields of fire about 180° for each gun. Elevation from horizontal about 90° for top gun and about 60° for bottom gun. About 3,600 rounds carried.

Steel plate about 50 cm wide, 60 cm long, 1.5 cm thick between engine and cockpit ahead of oil tank in position shown in POW's sketch below:
Fuel Protection
POW said that formerly JILL 12 fuel tanks were lined with about 5 cm of fairly effective protective rubber lining, but that because this reduced fuel load and range, new planes lack this protection. He observed that the pilots did not like it, preferring fuel to safety, and often got the lined tanks changed.

Estimated that about half of JILL 12 are equipped. Lead plane, at least, likely to carry it. None on P0W's plane and details unknown. POW's sketches, however, based on observation of gear on other JILL 12 indicated YAGI antenna carried_ on the leading edge of port wing about 1/3 of the distance in from wing-tip and similar antenna on either side of the fuselage aft of the cockpit. Length of antenna on wing about one meter with dipoles equidistant apart. Projected forward. Fuselage antenna had dipoles projecting from fuselage at roughly right angles center-pole running roughly parallel to fuselage lines. POW said this was search radar to pick up ships and planes.
Oxygen Equipment 
Three oxygen bottles, each somewhat less than one motor high and about 10 cm in diameter, carried on the right side of the center seat. POW did not believe there was any oxygen-producing equipment carried.

About 1,550 liters maximum fuel load. No jettisonable tanks. 87 octane gas. No removable.

War Load
One torpedo (modification 7, type and model unknown) 800 kg or 1 x #80 800 kg bomb or 6 x #6 60 kg bombs. POW thought only one 250 kg bomb could be carried because of kind of bomb-carrying gear. He had had no experience, however. Water-methanol - 68 liters carried. Partial cut in up to five minutes continuous is allowable; 30-second continuous full cut in for absolute maximum speed is allowable. Tank located between oil tank and cockpit. ADI comes on automatically at 150 mm manifold pressure if pilot has previously engaged lever which sets automatic injection on.

Modification 7 (KAI NANA) Aerial Torpedo 
Typo, model, and technical details unknown. Speed 42 knots; fuel: alcohol, compressed air, fresh water system. One small flexible stabilizer (ANZENBAN) about 10 cm square on each side to prevent roll. Torpedo is armed by a small vein topside of warhead. POW called this the "safety-pin" (ANZENSEN). While pin is perpendicular to torpedo surface, torpedo is on safety. When the torpedo enters the water, pressure of motion forward bends pin back parallel to torpedo surface. The missile then explode upon  impact, probably, POW thought, on inertia principle. One gyroscope.

Launching Gear
Torpedo carried below fuselage with two guide clasps and one holding clasp (see POW's sketch below). A small can of explosive is carried at point B at the holding clasp joint. The pilot detonates this at release point by electric switch; the joint is forced apart and the torpedo drops. Rough sketch (not to scale) is drawn on next page.
Modification 7 can be dropped from 150 meters, but standard is 50 meters altitude.

Landing Guide Lights (CHAKURIKU SHIDO TO) 
These lights arc supposed to help the pilot avoid coming in too high or too low and overshooting or undershooting the runway at night. A frame containing about three blue lights is set flash on the ground close to the runway facing the direction of approach. About 5 meters diagonally ahead and closer to the runway a similar frame or red lights mounted on a stand about 70 cm high is set. These lights are set in such a position that if the pilot comes in too high, the blue lights appear to be above the red relative to his line and plane of descent. Conversely, if his approach is too low the red lights appear above the blue relative to his approach line. If he is coming in at the correct altitude and approach angle of descent, the red and blue lights appear to line up in one row. POW's sketch follows:


Pre-Flight Training
Nearly four months. Subjects studied included arithmetic, physics, communications (flag and radio Morse), navigation, military affairs, maintenance (KOTOBUKI model (KATA) 2), physical drill, cutter operation. Course very easy for POW after his education. Knew only of two failures.

Elementary Flight Training
Type 93 training plane. Total flying hours in this stage of training about 65 from 25 Jan 1944 to 30 April 1944. Flying hours included the following (all approximate):
Solo: about 10 flights totalling about five hours after about four and one-half flying hours.
Formation flying with instructor. Formation of three planes. About 15 hours and about 15 flights.
Aerobatics (SUTANTO from English stunt) including spins, loops, Immelman turns. About 25 hours with instructor; about 25 flights.
Instrument flying: about four hours, but not in bad weather and always with instructor.
Military formation flying: six planes, 12 hours, very few flights, with instructor.
Ground training at this stage included radio (Morse), about 100 hours maintenance Type 93 trainer, about 60 hours aerial navigation, about 20 hours of pilot ground training including Link Trainer.

Combat Plane Training 
Type 97 KATE. Total flying hours about 60 at this stage, from 30 April 1944 to 28 Aug 1944 at TAINAN. Flight training included about one hour solo (two flights), about 40 hours flying with instructor (DOJO HIKO KUNREN), and about 20 hours flying with other trainees (GOJO HIKO) trading off on controls. Team rides included about seven hours of blind flying, but never in bad weather. POW also had about three hours of blind flying with instructor. Blind flying included level flight, glide, and climb at fixed speeds, but POW had no training in blind landings or take-offs. It also included standard rate and double rate turns. POW observed that under then current and present conditions, there is no time for training in blind landings and take-offs at this stage. 
Flight hours also included formation flying (3 planes) and, on about two occasions, multiple formation. Single-plane dummy runs against land targets (stationary) and formation runs against fishing boats were practiced. No dummy torpedoes were dropped, however.
Ground training at TAINAN was practically a review of training received at TAKAO, but with very little communications. It included Link Trainer, using a model of KATE. There was some study of KATE's engine, but POW could not recall any details.


POW was taught that standard run-in altitude is 50 meters, as is torpedo release altitude. Release distance is 1,000 meters. In his only actual attack (sec Sec 3) POW came in at proper altitude, but released his torpedo at about 1,500 meters because of heavy AA fire and a "mistake as to distance." Standard evasive maneuver is to swing from side to side with little change in altitude. Where approach is over water, run-in usually commences at about 10,000 meters from target, though this may vary according to circumstances. Speed 180-200 knots IAS - full speed with ADI.
No fixed altitude. In his only mission, however, POW's approach altitude was 150 meters. POW ascribed this first to the fact that in a night attack the low altitude enabled the navigator to see the sea surface to check wind direction and secondly to avoidance of radar detection. Approach speed about 125 knots IAS in POW's attack.
Formation breaks at about 10,000 meters from target and two after planes swing around to hit opposite side. Approach begins at about 50,000 [5,000?] meters from target, 200 meter altitude, take distance about 200 meters, take height about 50 meters, speed cruising (120-130 knots). Run-in from about 10,000 meters distance, column formation on both sides of target, 50 meters altitude, each element of two planes one side simultaneously. Other run-in data as explained under Run-In above. POW had practiced this attack against a DD about five times at KATORI, using Modification 3 torpedo (type and model unknown) with charge removed.

Envelopment Attack (HOI KOGEKI)
POW had done this in practice once at USA. He sketched and described it as follows:
The eight-plane multiple formation splits at at least 20,000 meters from the target, at altitude of about 3,000 meters. Aft formation of four planes swings around to opposite side of target as shown. All planes take approach altitude of about 200 meters from break-up of multiple formation. From 10,000 meters from target or as soon as enemy sighted, the four planes in each group deploy as shown and begin run-in. Run-in interval, wing-tip to wing-tip, was about 500 meters. Other run-in data as previously set out. Attack is simultaneous from each side.
In the event that time or circumstances do not permit this type of envelopment, one formation of four planes swings right, the other left, so that on run-in envelopment is as follows on next page:
"Wheel formation" (KURUMA GAKARI). POW had never tried this, but had learned it only from models while at USA. He described and sketched it as follows:
Radius of circle (from target) approximately 8,000 meters. Altitude of planes at circumference about 1,000 meters. Speed of planes at circumference about 120-130 knots. Run-in data from circumference as previously described. Planes were to attack as opportunity offered, according to the judgement of the individual pilots. The maneuver may be either counter-clockwise (HIDARI MAWARU) or clockwise (MIGI MAWARU).
Two-plane night attack: POW had practised this attack three tines at KATORI. Target illuminated by planes from recce plane. Approach at 200 meters altitude (oversea), formation thus . Run-in from 10,000 meters from target, column-formation, speed full, altitude 50 meters, release distance 1,000 meters. Column formation from commencement of run-in. Flares are dropped in night torpedo attacks at order cf lead attacking plane to recce plane or planes.

A metal-coated paper package released by hand and unrolled by string catch, releasing 100 or more sheets about 5 cm wide and one foot long. Plane carried about six packages. One to be dropped at a time. Dropped in case of US night fighter attack or on attack against ship target. Immediately after dropping, course changed.

Target Priorities
In case of a carrier Task Force, target importance for torpedo-plane attack CV, BB, CA, CL, DD in that order. POW was ordered to give first priority to transports, then warships in order as above. He received no description of AGC or  order to attack it first, but said that he would attack such a ship first if he knew of it. If en route to Okinawa had encountered a target, he would have radioed its position, but would have continued his mission unless the target were a carrier and its planes prevented his going on. In that case he would have attacked the carrier.

Suicide Pilots 
No experience or training as such. While POW was at USA in late 1944 a volunteer notice (GANSHO) was received asking instructors to volunteer for this duty. Not all the instructors did so, but most, including POW, did. Nothing came of it in POW's case, but he expected that he would have become a fighter pilot had he become a suicide man. He thought that mostly very young men of little experience became suicide pilots. While POW was with the K-256th HIKOTAI at KATORI in early 1945, the outfit had a chance to volunteer as a suicide unit. The HIKOTAI CO, however, turned down the opportunity. POW noted that not everybody is in sympathy with throwing away pilots and planes. Had the CO decided to accept, however, all the unit would have followed him perforce.


Aviation Fuel
POW understood that USA flying hours had been about 80 for combat-plane trainees until about March 1944. Gradually, they have been cut down at USA and presumably elsewhere to about 60 hours owing to gasoline shortage.

POW was not aware of any lack of plane spare parts, at least for ordinary maintenance requirements. He understood from maintenance people, however, that quality was not up to earlier standards frequently, but know no details.


Operational Failures JILL 12
Out of the some 35 JILL 12 in POW's outfit at KATORI about four per day on the average were non-operational as a result of dirty spark plugs, a condition in turn caused, POW thought, by some defect in the carburetor.
Four JILL 12 were lost in training of K-256th HIKOTAI at KATORI. One of these was destroyed when during a training run-in with AA avoidance tactics the rudder broke under the strain of weaving from side to side. Causes of other crashes not known, but POW heard that somehow dew from the wings might have gotten into the gas, probably from the dew which he said formed easily around the mouth of the gas in-put pipe.

---The information herein has been obtained from Prisoner of War sources and must be judged accordingly--- 

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