2-63. When it needs to shift 2-64. 2-65. 2-66. broadcast guard, a ship sends what type of message? 1. Termination  request message 2. Communications  guard shift 3. Service  message 4. Broadcast  screen  request Broadcast  screen  requests should be sent to what organization? 1. Broadcast  rerun  station 2. Broadcast  radiating station 3. Broadcast  control station 4. Broadcast  keying  station A COMMSPOT report should be sent under what circumstances? 1. 2. 3. 4. As soon as unusual communication difficulties  arise As soon as communication difficulties  are corrected Whenever  unusual communication difficulties  are expected Durinq  solar  flare-ups What type of message is placed  in  the  cryptocenter file? 1. SPECAT 2. SPECAT  SIOP-ESI 3. TICON 4. NATO A. Authentication B. Codes C. Ciphers D. Radio  silence E. Monitoring F. Identification  Friend or Foe (IFF) Figure 2A IN  ANSWERING  QUESTIONS  2-67  THROUGH 2-72,SELECT  THE  SECURITY  DEVICE  OR PROCEDURE FROM FIGURE 2A THAT IS BEST DESCRIBED IN THE QUESTION. 2-67. Any  cryptologic  system  in which  arbitrary  symbols  or groups  of  symbols  represent units of plain text. 1.    A 2.   C 3.   E 4.   F 2-68. Uses   electromagnetic transmissions  to  which equipment  carried  by friendly  forces automatically  respond. 1.   B 2.   C 3.   E 4.   F 2-69. A  procedure  designed  to protect   communications systems  against  acceptance of  false  transmissions  or simulations  by  establishing the validity of a transmission,  message,  or originator. 1.   A 2.   B 3.   C 4.   D 18