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[Dreamk]

With the uploading of the new extended Torpedoes pack (https://www.sas1946.com/main/index.php/topic,46400.msg516525.html#msg516525), detailed performances data could be found in the pdf document attached to the pack, but the need was felt of details upon the historical back ground of these torpedoes.

So let's begin with the Japanese Aerial torpedoes
(A photo catalog of the various model appears in the main post of the Torpedoes pack https://www.sas1946.com/main/index.php/topic,46400.msg516528.html#msg516528 )

Torpedoes were designed by the year of their year of development, and their sub-model.

• Type 91 stands for Japanese year 2591 = Gregorian (Western) year 1931
• Type 94 stands for Japanese year 2594 = Gregorian (Western) year 1934
• Type 4 stands for Japanese year 2604 = Gregorian (Western) year 1944

The sub-models were designed by “mod” followed by an ordinal number, and from 1944 onwards by “mark” followed by an ordinal number.

The confusion often existing in the appellation of Japanese torpedoes is due to the fact that both torpedo bodies (propelling unit) and warheads were also classified by models using a similar same designation system of “mod” followed by and ordinal number

Torpedo Body                    91 mod                                91 mod 2                            91 mod 3                            91 mod 3 improved            91 mod 3 strong ("mod 5") 91 mod 3 strong ("mod 5") 91 mod 3 strong ("mod 5") 91 mod 3 strong ("mod 5") Type 4                                Type 4                                Type 4

Torpedo Warhead                    91 mod 1 91 mod 2 91 mod 3 91 mod 3 91 mod 3 strong 91 mod 4 91 mod 7 type 4 (V-head) mark 2 mark 4 type 4 (V-head)

Torpedo Designation                    91 mod 1 91 mod 2 91 mod 3 91 mod 3 improved 91 mod 3 strong 91 mod 4 strong 91 mod 7 strong 91 mod 3 strong with type 4 head Type4 mark 2 Type4 mark 4 Type4 type 4

(The “V-head”, was a shaped charge type (hollow charge) introduced in 1944. Only three of these ‘V' heads were used in combat before the war ended.)

• The torpedo type 91 mod 1, was introduced in 1931, and was still in service ten years later, being used successfully against the HMS Prince of Wales and HMS Repulse on 10 December 1941.
• In 1941, torpedo type 91 mod 2 was introduced. It had an increased explosive charge, anti- roll stabilizers, and eight metal fins, enabling the attachment of a specially devised tail stabilizer for drop in shallow waters. This was the main torpedo used at Pearl Harbor.
• In 1942, the torpedo type 91 mod 3 was introduced. It had an increased explosive charge and initially 8 tail fins.
• The torpedo type 91 mod 3 improved, introduced in 1943, enabled launching speed up to 555 km/h.
• The torpedo type 91 mod 3 strong, introduced in 1944, had an increased explosive charge and allowed launching speeds up to 648 km/h – but its range was reduced to 1500m
• The torpedo type 91 mod 4 strong, introduced in 1944, had a still increased explosive charge
• The torpedo type 91 mod 7, strong, introduced later in 1944, had an further increased explosive charge.
• The torpedo type 91 QS, was a standard Type 91 torpedo modified for attacks on submerged submarines. On water entry it was designed to circle and descend at the same time. The initial diameter of the spiral was about 290m, and the torpedo could continue this down to some 100m. 50 such torpedoes were made in 1945 and some issued to units but no record of their use has survived.
• The torpedo Type 94, was an oxygen-fuelled torpedo. However the main advantage of such a torpedo, the extensive range, was judged as not required from an aircraft torpedo.
• The torpedo type 4, introduced in April 1945 had a further strengthening, and the launching speed increased to 740 km/h.
• The torpedo type M developed during the years 1942-1944 had a larger diameter, and was considerably heavier, around 2 tons with a 750kg explosive head, and could be launched at speeds up to 555 km/h. It does not seem to have seen operational service as its carrying aircraft, the 4-engined Nakajima G8N, was not produced in numbers.
• The torpedo type 4 mod 6 was and antisubmarine weapon designed to be dropped from a height of 100 m, assume a linear trajectory with a glide ratio of 3 to 1, enter the water and spiral downward describing circles 80m in diameter, spaced at depths of 80m.

The main differences between type 91 mod 3, 4 and 7 strong were the size of warhead used.

Operational torpedoes were left in a bare metal condition and coated with a light film of oil. A 4mm thick black latex rubber sheath, extending back 24" from the nose of the torpedo, aided in cushioning water impact shock. This sheath would shatter on impact.
Sometimes the latex used was in natural color instead of black, and then the sheath looked then creamy white.
Plywood fins were unpainted, but on the Soryu, at least, they were painted in order to look as made from metal.
Practice warheads of torpedoes were painted with different colors, either in black , red , or other colors. In sea exercises, the differentiating colors would tell from which fleet they came from when the warheads were recovered afterwards. The colors used by each fleet were red, white, black, green, yellow, brown, and blue. Once a fleet was allotted with a color, it used the same color over long periods. The color sequences were applied according to carrier seniority, in the following order: red, white, yellow, green, brown and black. The black of practice torpedoes warhead was due to paint not to a latex sheath.

Different modifications to the wooden tail fin array were used on the various Japanese torpedo models. Early wooden fins appeared during the Sino-Japanese conflicts and were made of 6 wood planks.

Three main types of aerial tail frames were used:

• The 6-fins wooden array, already used in the Sino-Japanese conflict and at Pearl Harbor, appears to have been used only on the Type 91 modified by having eight metal tail fins
• The Box Type Tail Frame gave the best performances and its large size originally restricted its use occasionally on torpedoes which were slung under the fuselage of a plane. A later model, more compact, appeared in 1944.
• The 4-fins X-Type Tail Frame was less effective but cheaper and easier to produce. Made of 4 planks with two cross braces, attached to the fins, its main advantage was in its adaptability to all types of torpedo planes. It is possible that an early model of such a tail frame was also used at Pearl Harbor, along the 6-fins model. In mid 1944 appeared an improved design, constructed of planks of heavier thickness, eliminating the need for reinforcing braces.

There were also two sizes of wooden frames for the anti-roll flippers. They were wing-shaped and consisted of two half sections bolted together around the flippers. Their aim was to reduce the tendency of the torpedoes to roll in the air after release from the aircraft. The larger size was used originally, but a smaller type was finally adopted because of the restricted openings in bomb bays. On impact, these auxiliary wooden "winglets" broke away, and the metal roll-control flippers, geared to the gyro-mechanism of the torpedo, took over their anti-roll function in the water.

Torpedo Designation Japan Type 94 mod2 Type91 mod1 Type91 mod1 Tail1 Type91 mod2 Type91 mod2 Tail (1,2,3) Type91 mod3 Type91 mod3 improved Type91 mod3 strong Type91 mod3 Type4 Type91 mod4 strong Type91 mod7 Type91 mod7 Tail (3,4) Type91 mod2 QS Type4 mark2 Type4 mark4 Type M (Shisei Gyorai 533) type4 mod6 AS

Max drop speed (km/h)   268 190 220 460 460 481 555 648 648 648 648 648 460 741 741 555 270

Min Drop Height (m)   30 30 30 30 30 40 40 40 40 40 40 40 30 40 40 40 40

Max Drop Height (m)   100 100 500 200 225 200 200 200 200 200 305 330 200 305 305 350 100

Weight (kg)   848 784 784 838 838 848 857 848 920 920 1052 1052 838 984 1105 2070 270

Explosive (kg)   150 149.5 149.5 204 204 235 235 235 462 308 420 420 204 313 417 750 100

Speed (km/h)   88 78 78 78 78 76 76 76 76 76 76 76 47 76 78 93 11

Range (m)   3000 2000 2000 2000 2000 1500 1500 1500 1500 1500 1500 1500 3700 1500 1500 2500 400