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Page Title: Shipboard ASW Organization
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The substance through which sound travels is called  a  medium.  All  types  of  matter  are  sound mediums  of  varying  efficiency.  The  denser  the medium, the more rapidly sound travels through it.  Therefore,  steel  is  a  better  medium  than  water, and water is a better medium than air. Let us take a look at what happens to a sonar impulse   after   it   leaves   the   transducer   (the transmitting device in the water). The transducer introduces  the  sound  wave  into  the  water  by converting the equipment’s electrical energy into sound  vibrations.  The  impulse  travels  at  a  rate of   between   4,700   and   5,300   feet   per   second, depending  on  the  temperature,  salinity,  and pressure  of  the  water.  The  rate  of  travel  of  the impulse is four or five times faster than the speed of  sound  in  air.  However,  the  hazards  of  travel take  their  toll  on  its  speed  and  signal  strength. Current, bubbles, and wakes absorb some of the sound.  As  the  impulse  passes  through  foreign matter  such  as  seaweed,  silt,  and  animal  life  in the water, it scatters and becomes even weaker. As  the  sound  wave  travels  away  from  the transducer,  it  spreads  out  like  a  searchlight  beam. The further away it travels from the transducer, the  weaker  it  becomes. Once  the  wave  strikes  an  object  such  as  a submarine, that portion of the impulse which is at a right angle to the object reverberates toward the sonar receiver. Again absorption, scattering, and  spreading  will  affect  the  strength  of  the impulse.  However,  it  will  still  signal  a  possible target   unless   multiple   reflections,   or   echoes, such  as  reverberations,  self-noise,  and  a  high surrounding  noise  level,  drown  it  out. Multiple reflections, or echoes, can come from many  sources.  Sound  waves  bouncing  off  small objects such as fish or air bubbles produce small echoes.  Sound  waves  reflected  from  the  sea surface  and  bottom  also  cause  echoes,  and  the sea  mass  itself  causes  reverberations.  These reverberations   appear   on   video   and   audio receivers.  Reverberations  from  nearby  points  may be so loud on the audio receiver that they interfere with,  or  completely  mask,  the  returning  echo  from the target. SHIPBOARD   ASW   ORGANIZATION Sonar  control  is  the  major  shipboard  ASW station.   Other   stations   are   the   bridge,   the combat  information  center  (CIC),  and  the  ASW weapons batteries. On most ships this organization is  integrated  into  the  combat  systems  department. Sonar   control   is   the   ASW   station   that maintains  a  continuous  underwater  search  for submarines.  From  the  bridge,  the  officer  of  the deck   conns   the   ship,   keeping   other   control stations  informed  of  the  ship’s  maneuvers. The  combat  information  center  is  the  key station for coordinating search/attack operations within   the   ship   and   betweens   ships   and/or aircraft. Personnel in CIC plot, display, evaluate, and disseminate all air, surface, and subsurface contact information and recommend search plans to  the  commanding  officer. In  modern  ASW  ships,  the  captain  and  the tactical  action  officer  (TAO)  often  direct  the attack  from  CIC.  However,  the  CO  may  choose to  remain  on  the  bridge.  When  that  happens, repeaters duplicate information from CIC for the captain’s  use  while  phone  talkers  relay  amplifying information to him. That enables the captain (in conjunction  with  the  TAO  in  CIC)  to  evaluate critical  elements  of  the  attack  from  his  position on the bridge. After evaluating elements such as the target’s course and speed, the captain can then authorize  delivery  of  the  necessary  ASW  weapons. AMPHIBIOUS   WARFARE Amphibious   warfare   encompasses   many different  types  of  ships,  aircraft,  weapons,  and landing forces used in a concerted military effort on  a  hostile  shore.  An  amphibious  operation  is an  attack  launched  from  the  sea  by  naval  and landing  forces.  The  landing  forces,  transported by  afloat  landing  craft  and  helicopters,  may include  Army  and  Marine  Corps  troops.  During such  operations,  both  surface  ships  and  aircraft usually  bombard  the  hostile  shore  immediately before  the  landing. Amphibious   operations   are   conducted   to establish a landing force on a hostile shore to do all  of  the  following  actions:  to  prosecute  further combat   operations;   to  obtain  a  site  for  an advanced naval or air base; and to deny the use of  an  area  or  facility  to  the  enemy. The  principle  type  of  amphibious  operation is the amphibious assault. The amphibious assault follows   a   well-defined   pattern.   The   general sequence   consists   of   planning;   embarkation; rehearsal; movement to the objective; and finally, assault  and  capture  of  the  objective. PLANNING The planning phase of an amphibious assault reflects the collected intelligence data on enemy 12-15

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