Type 93 Torpedo - Specification

Specification

Specification examples of ranges by speeds

• 22,000 m (24,000 yd) at 48 to 50 kn (89 to 93 km/h; 55 to 58 mph)
• 33,000 m (36,000 yd) at 37 to 39 kn (69 to 72 km/h; 43 to 45 mph)
• 40,400 m (44,200 yd) at 33 to 35 kn (61 to 65 km/h; 38 to 40 mph)

However, IJN announced officially the maximum performance of the Type 93 was 11 km (5.9 nmi; 6.8 mi) at 42 kn (78 km/h; 48 mph).

The stated range of over 10 km (5.4 nmi; 6.2 mi) was effective when the targeted warship steamed straight for more than a few minutes while the torpedo approached. This sometimes occurred when USN cruisers chased IJN destroyers breaking away from the scene of the battle at high speed during the night, or when American fleet carriers, engaged in flight operations, were targeted by IJN submarines in the South Pacific in 1942–43.

The Type 93 weighed about 2.9 short tons, with a high-explosive warhead weighing 490 kilograms (about 1,100 pounds).

Rear Admiral Jungo Rai explained this torpedo in the chapter Torpedo, in his book with a title that translates as "The Full Particulars of Secret Weapons", first published by Koyo-sha, Japan, in 1952.

The Type 93 torpedo has a main chamber filled with pure compressed oxygen, a joint regulator valve preventing reverse flow, and a small (approximately 13 liter) high-pressure air tank. First, compressed air is mixed with fuel, and the mixture is supplied to a heat starter. Ignition starts gently, with the mixture burning steadily in the engine (if oxygen is used at this stage explosions are common). As the compressed air is consumed and loses pressure, high-pressure oxygen is supplied from the main chamber through the joint valve into the compressed air tank. Soon the air tank is filled with pure oxygen, and powerful combustion continues in the engine.

The torpedo needs careful maintenance. Warships equipped with Type 93 torpedo launchers required an oxygen generator system to use this type of torpedo.

A design engineer officer of torpedo section, Kure naval arsenal of Imperial Japanese Navy, Ryozo Akagi (the 16th Class of the Imperial Japanese Navy Engineer Training School) explained the Type 93 with his notebook.

The structure of the Type 93 torpedo can be separated into several parts; from the front, warhead, air chamber, front float, engine compartment, rear float, tail rudders, screw propellers.

Type 93 rev.1 torpedo is equipped with an oil-fueled twin-cylinder reciprocating engine. The engine uses 2nd type air gas, a code name for 98% pure, high-pressure oxygen—the word "oxygen" was not used for secrecy. It can easily explode if an oil spot remains inside the anfractuous air pipes. Cleaning pipes is the most important maintenance task on the Type 93 torpedo, and takes 4 or 5 days. The practical use of the oxygen engine was the top secret in the Imperial Japanese Navy.

1st type air gas, a code name for air compressed to 230 atm, from a 13.5 liter tank, is used to start the engine.

The 2nd type air gas (oxygen) is stored at 225 atm in a 980-liter main chamber made by machining a block of nickel chromium-molybdenum steel, an alloy first developed for battleship armour.

The front of the torpedo contains the warhead, behind which is the shell of the 12mm (0.47 inch) thick main chamber. While the Type 93 is approximately 9 m (29 ft 7-1/4 in) long and 61 cm (24 in) in diameter, the 2nd type air main chamber is 348 cm (11 ft 5-3/8 in) long, occupying more than a third of the total length of the torpedo. Behind the main chamber is the rear section of the torpedo.

A pressure regulator reduces the decreasing pressure of compressed gas in the air chamber to the constant lower pressure needed to keep the torpedo running at constant speed.

Oxygen-fuel mixture is injected and exploded in combustion chambers of the engine heads, pushing pistons and rotating the single drive shaft. There are bevel gears on the shaft. The main shaft has an inner and outer drive shaft and drives coaxial double 4-bladed screws, contra-rotating so as not to rotate the torpedo.

The outer shell of the torpedo is made of steel panels 3.2 mm (0.126 inch) thick, but 1.8 mm (0.07 inch) thick at the rear, welded and water-tight. The plates at the engine section are designed to leak water to cool the engine.

There are two more controlling air tanks of total capacity 40.5 liters containing air compressed to 230 atm, to operate the rudders and stabilizers of the torpedo.

A depth meter controls the running depth. The water pressure board of the torpedo is manually set to 5 meters to set the running depth at 5 meters below the surface, and controls the side stabilizer to run at that depth.

The tail vertical rudder meter sets a vertical gyrocompass to control the vertical tail rudders. The gyrocompass guides the torpedo to the target, allowing even rear-launched torpedoes to turn around and hit a target in front. The tail rudders and side stabilizers are operated by air pressure.

The gyro is started when the torpedo is launched. The gyrocompass of Type 93 torpedo is 15 cm (5-7/8 in) in diameter and 7 or 8 cm (3 in) thick, spinning at 8,000 rpm. The Type 93 torpedo suffered from problems with this gyro speed when launched from a warship steaming at her top speed of around 35 knots.

The Imperial Japanese Navy initially tested the torpedoes at Dainyu, Aga-Minami of Kure city, Hiroshima prefecture, Japan, but the long-range Type 93 torpedo called for a relatively large area for launching tests. Subsequently, the test range at Otsu shima Island, Tokuyama city, Yamaguchi prefecture, next to Hiroshima prefecture was used. The base later became famous as the home base of the manned Kaiten "suicide torpedo".