The titles of commands or activities depicted in the heading of messages should be abbreviated in accordance with the Standard Navy Distribu- tion List (SNDL), parts I and II. The use of some abbreviations   in   the   heading,   such   as   ACT (action  addressee)  and  RR  (routine  precedence), is permitted for brevity. It is not necessary to list the type and hull number after the name of a ship. However, short titles or abbreviations should not be used in a message addressed to a member of Congress,   a   commercial   concern,   or   another nonmilitary  addressee. DATE-TIME   GROUP.—   Although  the  RP does   not   fill   in   the   date-time   group   block, knowledge  of  this  information  is  important. Messages are identified, referred to, and filed by the  date-time  group. The date-time group (DTG) is expressed in six digits plus a time zone suffix, a three-letter month abbreviation,  and  a  two-digit  year  designation. The  first  pair  of  digits  ( 05   0102Z   JAN   86) denotes  the  day  of  the  month,  the  second  pair (05 01 02Z JAN 86) the hour of the day, and the third  pair  (0501   02  Z  JAN  86)  the  minute  of the hour. These six numbers are followed by the time   zone   indicator,   in   this   case,   the   capital letter Z. Following the time zone suffix is the month, always  abbreviated  by  three  capitalized  letters: JAN,   FEB,   MAR,   APR,   MAY,   JUN,   JUL, AUG, SEP, OCT, NOV, DEC. The two-digit year is  expressed  as  85,  86,  and  so  forth. Duplicate   date-time   groups   should   not   be used by the same originator during any 24-hour period. Personnel in the communications center, when about to transmit two or more messages at nearly the same time, will usually shift the date- time  group  up  or  back  a  minute  or  two  so  that no two messages transmitted that day will have the  same  DTG. When asking the communications center for a copy of a message, the RP should refer to it by the DTG,  the  subject  line,  and  the  originator  of  the message.  Given  this  information,  communications center  personnel  can  usually  find  the  message quickly. SECURITY  CLASSIFICATION.—  Specific details  in  regard  to  security  measures  for  han- dling message traffic are contained in OPNAVINST 5510.1.   Department  of  the  Navy  Information Security  Program  Regulation.   Most   message traffic  handled  by  RP  personnel  is  unclassified. However,  all  message  traffic,  whether  classified or  unclassified,  should  generally  be  handled  on a  need-to-know  basis.  The  leading  RP  should 3-18 caution subordinates to be particularly careful to ensure the security of all messages. Precedence The heading portion of the DD Form 173 con- tains the PRECEDENCE block, which is usually completed  by  the  drafter,  although  it  may  be changed by the releasing officer. The precedence marking assigned is dictated by the subject matter of  the  text  and  the  desired  delivery  time. There  are  four  precedence  categories  with which  the  RP  should  become  familiar.  Each category   has   a   speed-of-service   objective   that indicates  the  maximum  desired  handling  and delivery time. These four categories indicate the following: .  The  originator’s  desired  speed  of  delivery of  the  message .  The  relative  order  of  processing  and delivery  that  the  message  should  receive  in  the telecommunications   center .  The  relative  significance  that  the addressee(s)  should  give  to  the  message The four precedence categories and their appro- priate  procedure  signs  (prosigns)  are  given  below. ROUTINE   (Precedence   prosign   R)—This precedence marking is assigned to those types of messages that justify electronic transmission but are   not   urgent   enough   to   require   a   higher precedence.   Examples:   Messages   concerning normal  peacetime  operations,  programs,  and projects;  stabilized  tactical  operations;  plans concerning   projected   operations;   periodic   or consolidated  intelligence  reports;  ship  movements; supply   and   requisition;   and   administrative, logistics, and personnel matters. Speed-of-service objective:  Within  6  hours. PRIORITY   (Precedence   prosign   P)—This precedence  marking  is  reserved  for  messages  that furnish  essential  information  for  the  conduct  of operations  in  progress.  Priority  is  the  highest precedence  normally  authorized  for  administrative messages.  (Exceptions  are  messages  reporting death, serious illness, or serious injury. These may be  assigned  Immediate  precedence.)  Examples: Situation reports on the position of a front where an  attack  is  imminent  or  where  fire  or  air support  will  soon  be  placed;  orders  to  aircraft formations or units to take actions that will coin- cide with ground or naval operations; immediate movement  of  naval,  air,  or  ground  forces;  weather observations with surface wind speeds 33 knots