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ccording to Dutton, 1934 and Bowditch, 1938, Navy regulations of 1920
mandated marking ship's clocks and logs and official communications
with the "zone description" of the time being kept. Bowditch, 1977,
page 477 states: " For certain communication purposes it is sometimes
convenient to designate a time zone by a single letter. The system
used is shown in figure 1814." This is the practice in the Army with
date/time groups. Using a letter allows army commanders in adjacient
zones to realize that the communication is using a different time zone
so that the appropriate correction can be made. Since army ground
operations do not, usually, span many time zones, it would be very
unusual for this to more than a one hour change. A one hour conversion
is easy to do in your head.  For navy and navigation purposes, which
may span many time zones and, for navigation, usually means finding
GMT no matter where you are on the earth, "zone descriptions" are much
more convient to use. For example, quick, how many hour must you add
to JULIETTE time to calculate GMT?  That was a trick question because
there is no JULIETTE zone. But the number of hours is not intuitive
and you must refer to a time zone chart to determine this number. So,
stick with "zone descriptions."

gl

On Aug 20, 3:08 pm, "Greg R."  wrote:
> I believe the letter designations are based on the offset from GMT
> (i.e. zone description) for the current time in use, without any
> reference to whether DST is being observed or not.
>
> Couldn't find any definitive answer to the question of this thread
> topic, so I'd guess the logical (and technically correct) answer would
> be that the letter designator would change during periods when DST is
> in effect, and revert back to the "normal" one when it's not.
>
> --
> GregR
>
> --- Bill  wrote:
>
> > The basic concept is clear to me, it is usage that I cannot track
> > down.
>
> > For example 0700 UTC/GMT would also be 0700 Zulu.
>
> > Here in Indiana, USA I am in the eastern time zone at my home and on
> > portions of Lake Michigan. (Indiana time zones is its own amusing
> > topic.)
>
> > When on standard time I subtract 5 hours from UTC for zone time.
> > When on
> > daylight saving time I subtract 4 hours.
>
> > Therefore if 0700 UTC or Zulu, my zone time is either 0200 or 0300,
> > depending on whether or not daylight saving time is in effect.
>
> > The designator for my time zone is Romeo (R). If I attach R or Romeo
> > to the
> > time in comminations or in the log, how do I account for standard or
> > DST?
> > Or is it just assumed that when used with a letter it is always
> > standard
> > time?
>
> > Bill


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