A. Introduction
B. Head section of a Mark 15 type torpedo
C. Air system of a Mark 15 torpedo
D. Superheating system of a Mark 15 torpedo
E. Main engine of a Mark 15 torpedo
F. Control systems of a Mark 15 torpedo
G. Tail section of a Mark 15 torpedo
H. Aircraft torpedos
I. Other types of torpedoes
J. Above-water torpedo tubes
                                              I. Other Types of Torpedoes

12I1. General

All United States Navy gas-steam torpedoes are similar in principle to the Marks 15 and 13 described above. Electric torpedoes differ from the gas-steam type in respect to their main power plants, as described in article 12I3. In all the non-homing torpedoes, the steering and depth mechanisms are similar, if not exactly the same. And war heads and exercise heads, although they differ in size, are basically similar.

For these reasons, the discussion of other types of torpedoes will be brief, and will deal primarily with the features that distinguish them from the Mark 15 type.

12I2. Torpedoes Mark 14 type and Mark 23 type

These torpedoes are only 20 1/2 feet long, to fit in submarine tubes. The Mark 14 has two speeds. The low-power setting will give a range of 9,000 yards at approximately 32 knots, and the high-power setting, a range of 4,500 yards at 46 knots. Its war head contains about 700 pounds of high explosive.

There are no side-gear assemblies in the main engine of this torpedo. The two speed settings are obtained by changing the number of nozzle jets in use (two for low speed, five for high) and by altering the size of the restrictions in the air, fuel, and water delivery lines.

The Mark 14 torpedo has a governor whose function is to stop the torpedo, if the starting lever is tripped accidentally, before the engine develops excessive speed, and thereby to safeguard personnel and to prevent serious damage to the torpedo. Centrifugal force actuates the governor, closing a valve in the air line from the starting piston to the low-pressure side of the reducing valve, thus banking the air over the main starting valve and stopping the torpedo’s power plant.

The Mark 23 torpedo is a Mark 14 torpedo from which the speed-change mechanism has been removed, leaving all five nozzles open. The restriction valve is locked in high power, and thus the engine can be operated at high speed only.

12I3. Torpedo Mark 18 type

The Mark 18 is an electrically propelled torpedo designed for use in submarines. It is single-speed, designed to run for 4,000 yards at an average speed of about 29 knots. The primary advantage of the Mark 18 is that it is wakeless.

In place of an air-flask section this torpedo has a battery compartment, which contains a lead-acid storage battery, a hydrogen eliminator, and a ventilating system. The battery runs a 90-horsepower series electric motor (located in the afterbody) whose armature is connected by the main drive shaft and gearing to two counter-rotating propellers. Compressed air-required to close the starting switch, spin the gyro, and operate the depth and steering engines-is stored at 3,000 psi in three small flasks in the afterbody. The gyro is of “run-down” type. After the initial spin the air is shut off and the gyro is unlocked; the gyro wheel continues to spin of its own momentum. The war head contains about 600 pounds of high explosive.

12I4. Torpedo Mark 16 type

The Mark 16 is a single-speed 21-inch by 21 1/2-foot submarine torpedo. It is a gas-steam torpedo in which hydrogen peroxide (NAVOL), instead of compressed air, supplies the oxygen required for combustion of the fuel. This use of NAVOL rather than air allows the Mark 16 torpedo to carry as much explosive as the Mark 15 and to have greater high-speed range, while not exceeding the Mark 14 in size.

The head section of this torpedo is similar to that of the Mark 15. The second or flask section contains a small compressed-air flask, a fuel (alcohol) tank, a water compartment, and a NAVOL tank-the last completely surrounded by the water tank. The main engine, valves, and control devices are located conventionally in the midship section and afterbody.

The source of the oxygen and of part of the water for the combustion cycle of these torpedoes is the NAVOL, which is a solution of hydrogen peroxide (H202) in water. Hydrogen peroxide, passing through a chamber containing a catalyst, decomposes with evolution of heat, to form water (steam) and oxygen. The oxygen unites with the fuel (alcohol) in the combustion pot, combustion being initiated by an igniter of conventional type. The resulting hot gases mix with steam and drive the main-engine turbines. Part of the steam comes from the breakdown of the H202 and part from additional water from the water compartment which is sprayed into the combustion pot to control the temperature.

By using NAVOL, the torpedoes require no air except (1) to force fuel, NAVOL, and water from their storage compartments to the combustion flask, (2) to drive the gyro, and (3) to operate the steering controls. As no air is fed to the combustion pot, no nitrogen is present in the exhaust to rise to the surface and leave the customary wake. There is, however, a small amount of nonsoluble gas resulting from the combustion of alcohol, which is forced out of the exhaust, leaving a very small wake that is practically invisible except in flat, calm water.

The main engine is a turbine with reduction gearing, similar in principle to the engine in a Mark 15 torpedo, but differing radically in mechanical detail. The turbine axis is horizontal instead of vertical, for which reason this engine is referred to as a “horizontal” or “H” engine, and spur gears rather than bevel gears are used for speed reduction.

12I5. Electrically set torpedoes

In the torpedoes described above, the gyro angle and running depth are ordinarily set mechanically, by inserting a spindle into the setting socket and turning it. Mark 14 and Mark 15 torpedoes have an additional socket for the speed setting. Obviously, all spindles must be withdrawn from their sockets before the torpedo can be fired.

In several modifications of the torpedoes mentioned above, and in practically all homing torpedoes, the settings are made electrically, rather than mechanically. A multi-conductor cable enters the breech of the torpedo tube, and is connected by a plug and socket to a similar cable that enters the afterbody of the torpedo. When the proper electrical inputs are supplied through the cable, servomechanisms in the torpedo automatically set the proper depth and gyro angle (and make the proper speed setting if the torpedo has a speed-change mechanism). At the instant of firing, the cable is automatically cut off close to the torpedo.

The electric setting system has several advantages. Its settings are relatively exact, and it eliminates several sources of error inherent in the mechanical setting system. Electric settings can be made right up to the instant of launching, since the cable is not cut until after the torpedo begins to move forward in the tube. And the electric setting system can easily be integrated with the advanced fire control systems, so that the setting signals are supplied automatically.

Except for the short length of cable that protrudes from the afterbody, an electrically set torpedo is identical in external appearance with mechanically set torpedoes of the same mark number.

12I6. Homing torpedoes

The torpedoes described above are designed to take up the course set on their gyro mechanisms, and then run in a straight line. Homing torpedoes can also follow a gyro course. In addition, a homing torpedo can search for a target, and, when it finds one, chase it until it secures a hit. Some types can switch back and forth between gyro control, search pattern, and homing control, as appropriate. Several types of homing torpedoes are now in the Fleet, and others are in various stages of development. For security reasons, only a short and very general discussion can be given here.

At present, homing torpedoes are acoustic (operated by sound). In general, they are of two types-active and passive. The active type sends out short pulses of sound, and “listens” for echoes from the target. When an echo is detected, the torpedo steers itself toward the source of the echo. The passive type merely listens for target sounds (such as propeller and machinery noises), then steers itself toward the source of the sounds.

The homing torpedo has the same safety devices as the air-steam type described above. Its exploder is armed both mechanically and electrically, and remains safe until the torpedo has traveled a safe distance from the firing ship. The homing mechanism also has an arming feature, so that it remains inoperable (with the torpedo on a gyro course) until the torpedo has traveled through a preset distance. One or more additional safety features not found in nonhoming torpedoes are present in all homing torpedoes.

Homing torpedoes, almost without exception, are powered by electric motors and batteries. In shape and external appearance they are quite similar to the nonhoming torpedoes already described. Several types are somewhat smaller than air-steam torpedoes, in length, diameter, or both. And several types have a single propeller, rather than two.