Call Signs The following call signs are authorized for use in calling and answering: visual, international, tactical, task organization, collective, and indefinite. Address groups may be used as call signs by Coast Guard and   Navy   commands   (except   in   non-military communications.) Call signs and address groups in message headings will ordinarily be arranged in alphabetical order in the form in which they are transmitted, whether plain, encrypted, or mixed. For this purpose, / (slant sign) and  figures  Ø  through  9  will  be  considered  the twenty-seventh  through  thirty-seventh  letters  of  the alphabet. Care must be taken to avoid separating groups of related call signs or conjunctive address groups,  which  are  interdependent. The different methods of visual signaling require variations in procedure for calling and answering. The necessary  instruction  for  each  method  is  prescribed throughout this chapter. FLASHING LIGHT PROCEDURES LEARNING  OBJECTIVES:  Explain   the procedure for calling, answering, relaying, verifying, repeating, correcting, and receipting using directional and non-directional flashing light.  Identify  procedures  for  communicating with aircraft, with daylight signaling lantern (DSL), and infrared. The  two  forms  of  flashing  light  used  are directional and non-directional. Directional procedure is always employed when using a directional light. It is also employed when using a non-directional light when   the   call   is   that   of   a   single   station. Nondirectional procedure is one station transmitting to a number of other stations simultaneously by means of a light showing over a wide area. See appendix II for tips for sending and receiving flashing light. USE OF SIGNAL LIGHTS In wartime, the greatest care is to be taken when signaling  at  night.  Flashing  light  is  to  be  used  only when necessary and a minimum of light employed except when making recognition signals. Then, a light of sufficient brilliancy must be used to ensure its being immediately   seen.   You   must,   however,   always remember that in heavy weather small ships have trouble reading dim lights. The background must always be considered, and care should be taken not to use a signaling light close to or in line with navigation lights. No upper-deck lighting should be visible on or in the vicinity of the signal deck. The use of signal lights at dusk and dawn must be avoided whenever possible. If, however, their use is unavoidable, you must pay constant attention to the brilliancy of their light. At night, a constant watch is to be kept on the ship of the OTC by all other ships. It may be found, after communication   has   been   established,   that   the brilliancy of the light can still be further reduced. It is absolutely  essential  when  using  any  type  of  directional light to keep it trained accurately throughout the transmission of the message. At  all  times,  ships  are  to  inform  other  ships signaling  to  them  when  their  lights  are  observed  to be brighter than necessary, by use of the prosign D. Frequently  test  sight  arrangements  of  lights  for alignment.   To   prevent   masthead   and   yardarm signaling lights from being accidently lighted, the switch in the power supply line should be kept open until use of the light is actually required. DIRECTIONAL  PROCEDURE The  transmitting  station  waits  for  the  receiving station to make a flash for each word, prosign, coded group,  or  operating  signal.  Should  the  receiving station fail to flash for the group, it will be repeated by the transmitting station until a flash is received from the receiving station. An exception to this rule is that a flash is not necessary to the prosign K when there is an immediate response to K. A flash should be made to K in the message ending when there will be a delay  while  checking  the  message  to  ensure  its completeness. NON-DIRECTIONAL  PROCEDURE This procedure permits one station to transmit to a number of other stations simultaneously by means of a light showing over a wide area. It is seldom used at night in wartime because of the danger of enemy interception.  It  may  be  used  by  day  or  night  in circumstances  where  the  risk  is  negligible.  The procedure  prescribed  for  the  non-directional  flashing 4-4