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NAVAL  OPERAT IO  'S AN D SUPPORT  FUNCT IO NS   53


         between  the  letters.  The  receiving signalman  flashes  a dash  after   A signalman  sends semaphore signals  by  moving  his or her
         each word  is received, meaning that it has been received and he or   arms in various positions representing each letter of the alphabet.
         she is ready for another.                              In  order to increase the range and visibility of movements,  he or
            Flashing light signaLing after dark can also be done with infra-  she holds  two hand  flags attached  to short staffs.  A good signal-
         red  lights  or  filters,  which  make  the  signal  invisible  unless  it  is   man can send or receive about twenty-five letter groups a minute.
         viewed  through  a special optical receiver.  Infrared  light signaling   Only thirty positions need to be learned.
         is called  Nancy. It is a very secure method of communication and   As  a point of interest, semaphore is often used as  an effective
                                     1
         can be used effectively up to about 7 /2 miles.        way to comm unicate with one another by civilian lifeguards man-
            Semaphore. Semaphore uses hand flags for short-distance com-  ning isolated lifeguard towers along lengthy public beaches.
         munications between ships. It is faster and more secure than flash-
         ing light.  At  night,  semaphore can  be done  using lighted  wands.
                                                                Sound and Pyrotechnic Signaling
         Ships  in  close  steaming  formations  or  alongside  for  underway
         transfer and replenishment operations commonly use semaphore.   Sound communications include whistles, sirens, bells, and under-
            Because  of its  speed, semaphore  is  better  than  other  visual   water acoustics. The first three are used by ships for sending a vari-
         means for long messages. Speed and security are the major advan-  ety of emergency warning signals.
         tages of semaphore. Its major limitation is its short range, Limited   These  include  navigational signals  prescribed  by  the  rules  of
         to only a few hundred yards.                           the road such as fog and maneuvering signals, air raid, breakdown,




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                                               Semaphore alphabet and  special  signals.
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