Quantcast Chapter 8 - GMLS: Secondary and Auxiliary Functions

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You should now have a pretty good understanding of the general physical arrangement and operational characteristics of the major guided-missile launching systems (GMLSs). The subject matter of this chapter will continue along those same lines. We will describe the secondary and auxiliary functions performed by the launching systems.

Secondary functions involve the equipments associated with guided-missile jettison and strikedown operations. Auxiliary functions cover a variety of equipment areas. We will only address the major types of fire suppression and environmental control systems. A brief section of general GMLS equipment safety precautions is presented at the end of the chapter. Pay close attention to the terminology used to describe each system.


Throughout this chapter, as well as in other areas of this manual, certain equipment or system operating procedures will be presented. This is for general training purposes ONLY. The information presented should NOT be misinterpreted as the absolute step-by-step sequence of events in any case. ALWAYS refer to and use the applicable reference instructions (GMLS publications, maintenance requirement cards, ship doctrines, and so on) when dealing with actual operational procedures.


LEARNING OBJECTIVES: State the purpose for missile jettisoning, and list the major components and operation of the dud-jettisoning assembly for the Mk 13 Mod 4 and Mk 26 GMLS.

Jettisoning, also known as dud jettisoning, is the act of clearing an unwanted missile from a launcher guide rail by ejecting it overboard. Whenever the firing key is closed, there is never a 100 percent guarantee that every missile will properly ignite and launch under its own power. A dud or misfire condition could exist that may lead to a potentially hazardous situation. Should the missile endanger the safety of the ship and its personnel or interfere with tactical operations, the order to jettison the round could be given. In some cases, however, after an appropriate waiting period, the missile may be safely returned to the magazine.

In any event, the final decision rests with the commanding officer. The orders to prepare to jettison and to actually jettison are relayed to GMLS personnel by the weapons control system (WCS). The launcher and jettison devices are readied for operation. Generally, a piston slowly extends out to contact the missile. The piston then ejects (or pushes) the missile over the side. The ejecting force is usually supplied by a high-pressure pneumatic source.


The Mk 13 GMLS uses a jettison device (fig. 8-1) that is an integral part of the launcher guide arm. Components of the device are located within the forward part of the guide arm and the yoke. (Also see fig. 7-6.) The jettison device is essentially a high-pressure, hydropneumatic ram-type piston. Jettison operations may be performed in the remote, local, or exercise modes as selected by the EP2 panel operator.

Physical Description

The main jettison components in the guide arm are a piston, a beam, a track, two shafts, and a latch. The piston, working from hydraulic and nitrogen pressures, is the propelling force. In extending, the piston moves the beam and the two shafts, pushing the missile from the retractable rail. With the retractable rail retracted, a crossbar receiver on the beam engages the crossbar of the two shafts. The beam, attached to the forward end of the piston and riding on rollers, is guided onto the beam track. The shafts are two tubes that slide into

Figure 8-1.-Mk 13 Mod 4 GMLS jettison device.

bores within the retractable rail. The crossbar receiver engages the shafts and latches them to the beam. Two pawls below the shafts engage the missile forward shoe. The latch is a spring-loaded valve that extends its plunger into a recess of the beam. The latch locks the beam and jettison piston in their retracted positions.

Other jettison components are in the yoke section of the guide. They include a pressure intensifier pump, a nitrogen tank, and a booster and charging valve block. The pressure intensifier pump is a special pumping unit

for boosting hydraulic pressure when retracting the jettison piston. The increased hydraulic pressure offsets the high nitrogen pressure used to extend the piston. Attached to the pressure intensifier pump is a shutoff valve block and solenoid assembly. It opens or closes the hydraulic fluid pressure line to the launcher guide components. The nitrogen tank is a steel flask charged with nitrogen. This pressurized gas extends the jettison piston at the velocity needed to eject a missile overboard. The booster and the charging valve block are part of a hydropneumatic unit. This unit also contains a piston and shutoff valves. The valves are used to maintain the nitrogen supply and hydraulic pressure at the proper level for operating the jettison piston.

Portable nitrogen supply cylinders (bottles) and a nitrogen booster pump supply nitrogen to the tank. Supply cylinders normally are charged to only 1,800 psi. This is insufficient pressure to operate the jettison device safely. A manually operated nitrogen booster pump is, therefore, used to increase supply cylinder pressure. The pump increases nitrogen pressure to about 2,400 psi when the nitrogen tank is filled or recharged. The Mk 13 Mod 4 GMLS has a permanently installed unit in the inner magazine structure.


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