Q3.  Yo u a r e fi n i s h e d u s i n g t h e h e a d s e t sound-powered phone. You should then unplug the headset for what reason? Q4.  When using a handset sound-powered phone, what action should you take to talk or listen through the phone? SOUND-POWERED CIRCUITS Learning Objective: When you finish this chapter, you will be able to— Recognize the function of the primary, auxiliary, and supplementary systems of a sound-powered circuit. Sound-powered telephone circuits aboard ship fall into  three  categories—primary,  auxiliary,  and supplementary systems. The primary   system includes  all  circuits necessary  for  controlling  armament,  engineering, damage  control,  maneuvering,  and  surveillance functions during battle. These circuits are designated JA through JZ. The    auxiliary  system    duplicates  many  of  the primary circuits for the purpose of maintaining vital communications  in  the  event  of  damage  to  the primary system. Auxiliary circuits are separated as much  as  possible  from  primary  circuits.  Circuit designations  are  the  same  as  the  primary  system, preceded by the letter  X  (XJA, X1JV, and so on). The  supplementary system, X1J through X61J, consists of several short, direct circuits, such as from the bridge to the quarterdeck or from the quarterdeck to  the  wardroom.  Circuits  in  the  primary  and auxiliary  systems  can  be  tied  together  at  various switchboards or individual stations may be cut out of the circuits, but the supplementary system does not have  these  provisions.  Because  circuits  in  the supplementary system usually are not manned, most circuits contain a buzzer system so that one station can  alert  another  station  that  communications between the two are desired. Circuit designations are characterized by a letter and number code. The 21JS4 primary battle circuit, for example, is identified as follows: numerals 21 indicate the specific purpose of the circuit; the letter  J  denotes sound power; the letter S means general purpose (radar, sonar,  and  ECM  information);  and  the  numeral  4 indicates a particular station in the circuit. The same circuit in the auxiliary system is X21JS4. All auxiliary and supplementary circuit designations are preceded by the  letter    X,  but  supplementary  circuits  are  easily identified as such because they have no letter after the letter  J. The  following  are  some  typical  shipboard sound-powered circuits: If you are on a lookout watch, your reports will go over the JL circuit to the bridge and the ship’s CIC. On small ships, the JL circuit sometimes is crossed with another circuit, such as the 1JV, to reduce manning requirements. The bridge talker then has the lookout, 4-5 Student Notes: JA Captain’s battle circuit JC Weapons control JL Lookouts 21JS Surface search radar 22JS Air search radar 61JS Sonar information 1JV Maneuvering and docking 2JZ Damage control X8J Replenishment at sea