"Military" time zones

Paul Eggert eggert at CS.UCLA.EDU
Sat Jan 10 07:22:27 UTC 2009

msb at vex.net (Mark Brader; please reply accordingly) writes:

> As you would know, there is a system of "military" time zone
> designations where zones are identified by a single letter:
> http://www.timeanddate.com/library/abbreviations/timezones/military/
> gives letter equivalents for zones from -12 = Y to +12 = M.
> I was having an email conversation with Russ Rowlett, who maintains
> the units-of-measurement site at <http://www.unc.edu/~rowlett/units/>,
> and we were wondering whether these single-letter designations are
> actually still used in practice -- and, if so, how time zones above
> +12 or not on integer hours are represented.  Is there an official
> reference for current practice on this anywhere?

Yes, please see the Combined Communications-Electronics Board general
communication instructions, dated 2007
<http://www.jcs.mil/j6/cceb/acps/acp121/ACP121H.pdf>.  These are
authoritative for the armed forces of Australia, Canada, NZ, the UK, and
the US.

Briefly: "N" is also used for UTC+13, "to provide for a ship in zone -12
keeping Daylight Saving Time".  There's no official provision for
UTC+14, but I presume that'd be "O".  For DST, use the corresponding
next letter (e.g., the eastern-US "R" becomes "Q" during DST.)

As for non-integer hours, the instructions simply say: "For time midway
between zones, both letters are used."

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