Military time zone

The military time zones are a standardized, uniform set of time zones for expressing time across different regions of the world, named after the NATO phonetic alphabet. The Zulu time zone (Z) is equivalent to Coordinated Universal Time (UTC) and is often referred to as the military time zone. The military time zone system ensures clear communication in a concise manner, and avoids confusion when coordinating across time zones. As the ACP 121 standard,[1] the military time zone system is used by the armed forces for Australia, Canada, New Zealand, the United Kingdom, the United States, and many nations in NATO.

Description

Going east from the prime meridian at Greenwich, letters "Alfa" to "Mike" (skipping "J", see below) represent the 12 time zones with positive UTC offsets until reaching the international Date Line. Going west from Greenwich, letters "November" to "Yankee" represent zones with negative offsets.

The letters are typically used in conjunction with military time. For example, 6:00 a.m. in zone UTC−5 is written "0600R" and spoken "zero six hundred Romeo".

The numeric zone description or "plus and minus system" indicates the correction which must be applied to the time as expressed in order to convert to UTC. For example, the zone description for the Romeo time zone is +5. Therefore, adding 5 hours to 0600R produces the time in UTC, 1100Z.[1]

Time zone nameDegrees longitudeDesignation
letter		Zone
description		Offset
Alfa Time Zone 7.5 E to 22.5 E A -1 UTC+01:00
Bravo Time Zone 22.5 E to 37.5 E B -2 UTC+02:00
Charlie Time Zone 37.5 E to 52.5 E C -3 UTC+03:00
Delta Time Zone 52.5 E to 67.5 E D -4 UTC+04:00
Echo Time Zone 67.5 E to 82.5 E E -5 UTC+05:00
Foxtrot Time Zone 82.5 E to 97.5 E F -6 UTC+06:00
Golf Time Zone 97.5 E to 112.5 E G -7 UTC+07:00
Hotel Time Zone 112.5 E to 127.5 E H -8 UTC+08:00
India Time Zone 127.5 E to 142.5 E I -9 UTC+09:00
Kilo Time Zone 142.5 E to 157.5 E K -10 UTC+10:00
Lima Time Zone 157.5 E to 172.5 E L -11 UTC+11:00
Mike Time Zone 172.5 E to 180 M -12 UTC+12:00
November Time Zone 7.5 W to 22.5 W N +1 or -13 UTC−01:00 UTC+13:00
Oscar Time Zone 22.5 W to 37.5 W O +2 UTC−02:00
Papa Time Zone 37.5 W to 52.5 W P +3 UTC−03:00
Quebec Time Zone 52.5 W to 67.5 W Q +4 UTC−04:00
Romeo Time Zone 67.5 W to 82.5 W R +5 UTC−05:00
Sierra Time Zone 82.5 W to 97.5 W S +6 UTC−06:00
Tango Time Zone 97.5 W to 112.5 W T +7 UTC−07:00
Uniform Time Zone 112.5 W to 127.5 W U +8 UTC−08:00
Victor Time Zone 127.5 W to 142.5 W V +9 UTC−09:00
Whiskey Time Zone 142.5 W to 157.5 W W +10 UTC−10:00
X-ray Time Zone 157.5 W to 172.5 W X +11 UTC−11:00
Yankee Time Zone 172.5 W to 180 Y +12 UTC−12:00
Zulu Time Zone 7.5 W to 7.5 E Z 0 UTC+00:00

The letter "J" ("Juliet"), originally skipped, may be used to indicate the observer's local time.[2] The letter "L" is also sometimes used to mean "Local" time, conflicting with its use for the Lima time zone.[3]

The letter "N" is also used to designate zone -13; this is to provide for a ship in zone -12 keeping Daylight Saving Time.[1]

The letter "Z" ("Zulu") indicates Coordinated Universal Time (UTC).

The ACP 121 standard actually refers to Greenwich Mean Time (GMT) as the base time standard,[1] but UTC has superseded GMT as a more precise time standard,[4] so the time offsets are commonly understood as UTC.[5][6]

History

Sandford Fleming devised a system assigning the letters A-Y excluding J to 1-hour time zones, which may have been the inspiration for the system.[7]

The standard was first distributed by NATO as a note in 1950. The note states "This method is based on the systems in use in the Armed Forces of these countries and the United States".[8] The British used a system of lettered zones, which was likely the direct influence.[9]

RFC 733 published in 1977 allowed using military time zones in the Date: field of emails.[10] RFC 1233 in 1989 noted that the signs of the offsets were specified as opposite the common convention (e.g. A=UTC-1 instead of A=UTC+1),[11] and the use of military time zones in emails was deprecated in RFC 2822 in 2001. It is recommended to ignore such designations and treat all such time designations as UTC unless out-of-band information is present.[12]

See also

References
  1. Combined Communications-Electronics Board (Oct 2010). ACP 121(I), COMMUNICATION INSTRUCTIONS – GENERAL (PDF) (Report). pp. 3A-1–3A-8. Archived from the original (PDF) on May 8, 2016. Retrieved Aug 8, 2011.
  2. "ATP 6-02.70 Techniques for Spectrum Management Operations" (PDF). Retrieved 2020-07-21.
  3. "Plans and Orders: Expressing Time", Army Planning and Orders Production, Field Manual 5-0 (FM 101-5) (PDF), Headquarters Department of the Army, United States Army, 20 January 2005, p. G11, Express all times in a plan or order in terms of one time zone, for example ZULU (Z) or LOCAL (L). I
  4. Morris, Doug (May 2008). "Time for the Weather: Translating Zulu". Weatherwise. 61 (3): 32–35. doi:10.3200/WEWI.61.3.32-35. S2CID 194035906.
  5. Leigh, Gabriel (17 November 2020). "Zulu and UTC: the story behind aviation's time zone". Flightradar24 Blog.
  6. "Military Time Zones". Veteran.com. 31 October 2022.
  7. Stromberg, Joseph (November 18, 2011). "Sandford Fleming Sets the World's Clock". Smithsonian Magazine. To this day, if you look at certain [military] maps that divide the world into time zones, the zones are assigned letters,
  8. Principal Staff Officers Committee (1950-06-15). SG 037: Method of expressing date and time in military messages (Report). NATO Archives Online.
  9. "Time Zones for Earhart Radio Message Database" (PDF). Finding Amelia Resource Library. Retrieved 2 June 2023.
  10. "Standard for the format of ARPA network text messages". Internet Engineering Task Force. November 1977.
  11. Braden, Robert T. (October 1989). "Requirements for Internet Hosts - Application and Support". Internet Engineering Task Force.
  12. Resnick, Pete (1 April 2001). "Internet Message Format". Internet Engineering Task Force.
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