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