CONVERTING   GMT   AND   LOCAL TIMES.— Most countries have adopted the GMT system. As a Radioman, you will need to be able to convert local time to GMT. To do this, you must understand the GMT system. Figure 2-9 is a chart showing the time zones of the world. Refer to the chart as you study the material in the next paragraphs. To  illustrate  converting  local  time  to  GMT,  assume that we are in zone R and the local time is 1000R (10 a.m.). Referring to the time chart in figure 2-9, you can see that zone R lies west in longitude from zone zero, and is designated plus 5. Therefore, we add 5 hours to the local time, 1000, to find that GMT is 1500Z. To convert GMT to local time, we reverse the process and subtract 5 hours from the GMT (1500Z) to obtain 1000R. The U.S. military services use the 24-hour system to express time in four-digit groups. The first two digits of a group denote the hour and the second two digits, the minutes. Thus, 6:30 a.m. becomes 0630; noon is 1200; and 6:30 p.m. is 1830. Midnight is expressed as 0000 (never as 2400), and 1 minute past midnight becomes 0001. Remember, to eliminate any possible confusion, never use 0000Z or 2400Z as the date-time group of a message. The correct time would be either 2359Z or 000IZ. We mentioned earlier that the 12th zone is divided by   the   180th   meridian.   This   meridian   is   the international date line (IDL) (figure 2-9). This is where each  worldwide  day  begins  and  ends.  A  westbound ship crossing the line loses a day, whereas an eastbound ship gains a day. This time zone is divided into literal zones MIKE and YANKEE. The eastern half of zone 12 is designated MIKE (-12), and the western half is designated YANKEE (+12). Now we come to a very important point in our discussion. Since MIKE and YANKEE are two parts of a single zone, the time in MIKE and YANKEE is always the  same.  When  the  IDL  is  crossed  from  either direction, the day must change. Since we have already established that there is a l-hour difference between each of the 24 time zones, it is clear that there is always a situation where it is a day earlier or later in one part of the world than it is in another. The primary point to remember about this zone is that it is always the same time in zone MIKE as it is in zone YANKEE, but it is never the same day! You can find more information on time zones in  Communication  Instructions  General  (U), ACP  121. Julian Date The Julian date consists of seven digits. The first three digits represent the day, and the last four digits represent the hour and minutes. The first day of the calendar year is Julian 001, and each day is numbered consecutively  thereafter.  For  example,  in  Julian 0311315, 031 is the 31st day of the calendar year (January 31), and 1315 is the filing time. PRECEDENCE The  message  drafter  indicates  the  desired writer-to-reader  delivery  time  (speed-of-service) through the assignment of a message precedence. Although the drafter determines the precedence, the releaser should either confirm or change it. (We will talk more about the responsibilities of the drafter, originator, and releaser later in this chapter.) Precedence  is  assigned  according  to  urgency,  based solely  on  speed-of-service,  not  according  to  the importance  of  the  subject  matter  or  the  text.  For example, an unclassified message may be assigned an IMMEDIATE  precedence,  whereas  a  Secret  message may be assigned a ROUTINE precedence. In this situation, the unclassified message requires fast action or response, whereas the Secret message may not require any action at all. The  following  paragraphs  list  the  various precedence  categories,  their  indicators,  and  basic definitions: ROUTINE (R)— This category is assigned to all types of traffic that justify electrical transmission but which are not of sufficient urgency to require a higher precedence. PRIORITY (P)— This category is reserved for messages that furnish essential information for the conduct of operations in progress. This is the highest precedence normally authorized for administrative messages. IMMEDIATE  (O)—  This category is reserved for messages relating to situations that gravely affect the national   forces   or   populace   and   which   require immediate delivery to addressees. FLASH (Z)— This category is reserved for initial enemy contact reports or operational combat messages of extreme urgency; message brevity is mandatory. YANKEE (Y)— In addition to the four major precedence   categories,   an   EMERGENCY COMMAND PRECEDENCE (ECP) is used within the 2-20