CONVERTING GMT AND LOCALTIMES.— Most countries have adopted the GMTsystem. As a Radioman, you will need to be able toconvert local time to GMT. To do this, you mustunderstand the GMT system. Figure 2-9 is a chartshowing the time zones of the world. Refer to the chartas you study the material in the next paragraphs.To illustrate converting local time to GMT, assumethat we are in zone R and the local time is 1000R (10a.m.). Referring to the time chart in figure 2-9, you cansee that zone R lies west in longitude from zone zero,and is designated plus 5. Therefore, we add 5 hours tothe local time, 1000, to find that GMT is 1500Z. Toconvert GMT to local time, we reverse the process andsubtract 5 hours from the GMT (1500Z) to obtain1000R.The U.S. military services use the 24-hour systemto express time in four-digit groups. The first two digitsof a group denote the hour and the second two digits,the minutes. Thus, 6:30 a.m. becomes 0630; noon is1200; and 6:30 p.m. is 1830. Midnight is expressed as0000 (never as 2400), and 1 minute past midnightbecomes 0001. Remember, to eliminate any possibleconfusion, never use 0000Z or 2400Z as the date-timegroup of a message. The correct time would be either2359Z or 000IZ.We mentioned earlier that the 12th zone is dividedby the 180th meridian. This meridian is theinternational date line (IDL) (figure 2-9). This is whereeach worldwide day begins and ends. A westboundship crossing the line loses a day, whereas an eastboundship gains a day. This time zone is divided into literalzones MIKE and YANKEE. The eastern half of zone12 is designated MIKE (-12), and the western half isdesignated YANKEE (+12).Now we come to a very important point in ourdiscussion. Since MIKE and YANKEE are two parts ofa single zone, the time in MIKE and YANKEE is alwaysthe same. When the IDL is crossed from eitherdirection, the day must change. Since we have alreadyestablished that there is a l-hour difference betweeneach of the 24 time zones, it is clear that there is alwaysa situation where it is a day earlier or later in one partof the world than it is in another. The primary point toremember about this zone is that it is always the sametime in zone MIKE as it is in zone YANKEE, but it isneverthe same day! You can find more information ontime zones in Communication Instructions General (U),ACP 121.Julian DateThe Julian date consists of seven digits. The firstthree digits represent the day, and the last four digitsrepresent the hour and minutes. The first day of thecalendar year is Julian 001, and each day is numberedconsecutively thereafter. For example, in Julian0311315, 031 is the 31st day of the calendar year(January 31), and 1315 is the filing time.PRECEDENCEThe message drafter indicates the desiredwriter-to-reader delivery time (speed-of-service)through the assignment of a message precedence.Although the drafter determines the precedence, thereleaser should either confirm or change it. (We willtalk more about the responsibilities of the drafter,originator, and releaser later in this chapter.)Precedence is assigned according to urgency, basedsolely on speed-of-service, not according to theimportance of the subject matter or the text. Forexample, an unclassified message may be assigned anIMMEDIATE precedence, whereas a Secret messagemay be assigned a ROUTINE precedence. In thissituation, the unclassified message requires fast actionor response, whereas the Secret message may notrequire any action at all.The following paragraphs list the variousprecedence categories, their indicators, and basicdefinitions:ROUTINE (R)— This category is assigned to alltypes of traffic that justify electrical transmission butwhich are not of sufficient urgency to require a higherprecedence.PRIORITY (P)— This category is reserved formessages that furnish essential information for theconduct of operations in progress. This is the highestprecedence normally authorized for administrativemessages.IMMEDIATE (O)— This category is reserved formessages relating to situations that gravely affect thenational forces or populace and which requireimmediate delivery to addressees.FLASH (Z)— This category is reserved for initialenemy contact reports or operational combat messagesof extreme urgency; message brevity is mandatory.YANKEE (Y)— In addition to the four majorprecedence categories, an EMERGENCYCOMMAND PRECEDENCE (ECP) is used within the2-20
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