| NAVAL ORDNANCE AND GUNNERY CHAPTER 12 TORPEDOES |
| B. Head Section of a Mark 15 Type Torpedo 12B1. General The head section may be either a war head or an exercise head. The war head is almost entirely filled with high explosive. The exploder is mounted in a cavity on the lower surface of the war head shell. For a test shot, or for firing practice, an exercise head is used in place of the war head. The exercise head contains no explosive charge, and no exploder mechanism. For an exercise shot, the exercise head is filled with a liquid ballast-either water or a solution of calcium chloride. At the end of an exercise run, the liquid ballast is automatically expelled. When the head is empty, the torpedo has enough buoyancy to float until it can be recovered. 12B2. Functional description The war head shell serves simply as a container to house the high-explosive charge and the exploder mechanism. Since the main charge of explosive is relatively insensitive to shock, an exploder mechanism is needed to detonate the main charge when the torpedo strikes the target. The exploder mechanism is so designed that, on impact with the target, it explodes a small detonator charge. The detonator then explodes a booster charge, which in turn detonates the main charge. When the torpedo is launched, the exploder mechanism is in a “safe” condition. It cannot explode the booster charge, even if its detonator explodes accidentally. During the first few hundred feet of the torpedo’s run, the exploder mechanism arms itself. When the torpedo reaches a safe distance from the firing ship, the exploder is completely armed. It will then detonate the main charge when the torpedo strikes any solid object. The exercise head simulates the war head during test firing. It has the same shape as the war head, and when filled with liquid ballast it has approximately the same weight. Thus an exercise torpedo has the same trim and running characteristics it will have when fired with a war head. At the end of the exercise run, compressed air from the torpedo’s air flask expels the liquid ballast through a discharge valve. An air-releasing mechanism releases the compressed air into the exercise head automatically when the pressure in the air flask drops to a predetermined value. 12B3. War head The Mark 15 type torpedo is provided with a Mark 17 war head. It is ogival in shape at its forward end, and cylindrical in its after part. A nose ring is provided at the forward end of the shell to facilitate handling. The shell itself is made of phosphor bronze. Although the Mark 17 war head uses only an impact exploder at the present time, the use of phosphor bronze rather than steel makes it possible to use an influence exploder when necessary. The high-explosive charge consists of more than 800 pounds of HBX. The lead ballast weight, mounted in the bottom of the war head shell, helps to control the trim of the torpedo and to minimize rolling. A joint ring at the after end of the war head shell is drilled and tapped for the joint screws that secure the head to the air-flask section. The after end of the shell is closed by a bulkhead, which is bolted to a flange on the inner side of the joint ring. A gasket between the bulkhead and flange forms a watertight seal. The exploder mechanism fits in a cavity in the bottom of the forward end of the war head. The exploder is mounted on a base plate, which is secured to the war head shell with screws. The base plate is curved to match the curvature of the war head. 12B4. Exploder construction Any one of several different exploder mechanisms may be used in the war head of the Mark 15 torpedo. The following discussion applies to the impact-operated Exploder Mechanism Mark 6. Figure l2B1 shows the location of the exploder in the war head. The booster charge is shown in outline, mounted above the exploder in the top of the exploder cavity. The arming action of the exploder mechanism is brought about by the impeller. The impeller is turned by the flow of water through the impeller channel in the exploder mechanism base plate. The horizontal shaft to which the impeller is keyed passes into the exploder cavity through a watertight packing. |
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| Figure 12B2 shows the Mark 6 exploder in both the unarmed and armed condition. The exploder’s principal safety device is the safety chamber, which may be seen at the top of the pictures. When the exploder is unarmed, the detonator is housed within the safety chamber. If the detonator should explode prematurely within the safety chamber, it could not detonate the booster charge. As the exploder arms, the detonator rises out of the safety chamber to its position within the booster cavity. On impact with the target, the detonator of the Mark 6 exploder is fired by a charge of electricity stored in a large condenser. During the first part of the torpedo run, the condenser is charged by the out-put of a direct-current generator driven by the impeller shaft. The generator output passes through a voltage-regulator tube, which keeps its voltage nearly constant regardless of generator speed. A second safety feature is provided by the delay device indicated in figure 12B2, part A. A spring-loaded contact grounds the generator output through the delay wheel. As the torpedo moves through the water, the delay wheel is turned by a worm on the vertical shaft (at the left in figure 12B2). After a short tune, a hole in the delay wheel reaches the spring-loaded contact. The contact falls into the hole, and the generator output is no longer grounded. At the same time, a blank sector on the wheel reaches the worm on the vertical shaft, and the wheel stops turning. |
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| Figure 12B3 shows the ball switch through which the detonator is fired on impact. Note that the left side of the pictures is forward; when the torpedo is under way the switch, as shown here, is moving from right to left. The ball is held in a cup-like depression by the force of the spring on the movable contact. When the torpedo strikes its target, the inertia of the ball carries it forward (to the left), overcoming the resistance of the spring and closing the contacts. The ball switch will operate even when the torpedo strikes the target a glancing blow. A sideways force on the ball will cause it to climb out of the cup, thus forcing the movable contact forward. 12B5. Exploder operation At the instant of firing, the exploder is in its unarmed condition. The detonator is completely housed within the safety chamber. The generator output is short-circuited to ground through the delay wheel. The inertia switch is open. As the torpedo moves through the water, the impeller wheel turns. The impeller shaft, through the gear train shown in figure 12B2, turns both the delay wheel and the safety chamber. The upper rim of the safety chamber is threaded on its inside, to match the threads of the detonator. The detonator is free to move up and down, but is so mounted that it can not rotate. Rotation of the safety chamber thus lifts the detonator up into the booster cavity. The delay wheel, meanwhile, un-shorts the generator. The generator, through the voltage regulator tube, charges the condenser. The exploder mechanism is then completely armed, both electrically and mechanically. On impact with the target, the inertia ball closes the switch contacts. The condenser discharges through the switch, and through the electric detonator. The detonator fires, exploding the booster. The booster detonates the main charge of high explosive. |
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| 12B6. Exercise head construction At the present time, Exercise Head Mark 31 is used with Mark 15 torpedoes. Figure 12B4 shows a sectional view of this exercise head. The exercise head has the same shape and size as the war head. And, like the war head, it is closed at its after end by a concave bulkhead. The exercise head, however, is made of steel rather than phosphor bronze. The war head is strengthened by the high-explosive charge, which completely fills it. Since the exercise head contains no explosive, it is reinforced by a series of nine strengthening rings. In the bottom of the exercise head shell, near the after end, is the discharge valve. This is a one-way valve, which keeps sea water from entering the head but permits the liquid ballast to be blown out at the end of the run. The air-releasing mechanism is mounted on a flange at the top of the exercise head shell, and connected by a length of pipe to a fitting in the bulkhead. The pipe is always provided with one or more loops, to prevent any danger of breakage due to fatigue. Two additional flanges, on which various accessories may he mounted, are provided at the top of the head. 12B7. Exercise head accessories One or more accessories are mounted on the flanges in the top of the exercise head, according to the conditions under which the exercise torpedo is fired. The headlight helps the recovery crew to locate a torpedo that has been fired at night. It contains a bulb and a set of flashlight batteries. An inertia switch in the headlight case turns the light on when the torpedo is fired. A torch pot helps in locating an exercise torpedo in the daytime. The torch pot contains a chemical that gives off smoke when it gets wet. A metal seal on the torch pot case is removed shortly before firing. When the torpedo is fired, water seeps into the case, and the torch pot begins to smoke. The depth and roll recorder is a mechanical device that helps in the evaluation of the torpedo’s performance during an exercise run. Throughout the run, it makes a continuous graphic record of the torpedo’s running depth and angle of roll. A pinger is a sound-making device. It is sometimes used when an exercise torpedo is fired in relatively shallow water. If the head fails to blow and the torpedo sinks, the noise of the pinger makes the torpedo easier to find. 12B8. Exercise head operation When an exercise torpedo is fired, the exercise head is filled with liquid ballast. The air-releasing mechanism is connected to the air flask through the fitting in the exercise head bulkhead, and through the blow valve on the flask. The blow valve is opened when the torpedo is prepared for firing. This allows compressed air, at full flask pressure, to reach the air releasing mechanism. Air pressure overcomes the pressure of a spring inside the mechanism, and closes its valve so that no air can enter the head section. During the torpedo run, the torpedo constantly uses air from its air flask, and the flask pressure slowly falls. When it reaches a certain predetermined level, it can no longer overcome the spring pressure in the air-releasing mechanism. The valve opens, and releases compressed air into the exercise head. Air pressure then forces the liquid ballast out through the discharge valve. 1289. Exercise firing and recovery Every torpedo is given at least one proof run before it is issued to the Fleet. In the Fleet, it will make one or more practice runs before it is returned to a tender for overhaul. An exercise torpedo is recovered from a boat that approaches from the lee side, to prevent any danger of drifting down on the torpedo. The torpedo is nearly vertical in the water, because of its empty head section. A noose is passed over the torpedo’s nose, and a line secured to the nose ring. The torpedo is towed slowly until it is nearly level in the water. The noose can then be worked aft and secured around the tail section. As a safety precaution, to keep the torpedo engine from starting up again, the stop valve is closed and a lock installed on the propellers as soon as these parts are accessible. The torpedo is then towed back to the firing ship. After hoisting an exercise torpedo aboard, the torpedo crew will perform a prescribed lubrication and maintenance routine to prevent corrosion and deterioration because of salt water. |