Military time zone

Going east from the prime meridian at Greenwich, letters "Alfa"{{efn|name=spelling|The official spelling is "Alfa", although this is often "corrected" to Alpha - see {{Section link|NATO_phonetic_alphabet#History}}.}} 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.

The letter "J" ("Juliet"), originally skipped, may be used to indicate the observer's local time.{{cite news|title=ATP 6-02.70 Techniques for Spectrum Management Operations|url=https://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/ARN19477_ATP%206-02x70%20FINAL%20WEB.pdf|access-date=2020-07-21}} The letter 'L' was previously misidentified in some editions of U.S. Army publications, such as FM 5-0,{{citation |title=Army Planning and Orders Production, Field Manual 5-0 (FM 101-5) |date=20 January 2005 |page=G11 |url=https://www.elon.edu/assets/docs/rotc/FM%205-0%20Army%20Planning%20and%20Orders%20Production%20.pdf |section=Plans and Orders: Expressing Time |publisher=Headquarters Department of the Army, United States Army |quote=Express all times in a plan or order in terms of one time zone, for example ZULU (Z) or LOCAL (L). I}} as representing 'Local' time, which conflicted with its established use for the Lima time zone (UTC+11). This error has been rectified in the latest edition of FM 5-0, released in May 2022,{{Cite book |title=FM 5-0: Planning and Orders Production |date=May 2022 |publisher=Headquarters, Department of the Army |pages=D-6 |quote=Order writers do not abbreviate local time as L. The abbreviation for the LIMA time is L.}} which no longer includes this incorrect usage. "LT" may instead be used to denote local time.

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

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, but UTC has superseded GMT as a more precise time standard,{{cite journal |last1=Morris |first1=Doug |title=Time for the Weather: Translating Zulu |journal=Weatherwise |date=May 2008 |volume=61 |issue=3 |pages=32–35 |doi=10.3200/WEWI.61.3.32-35|bibcode=2008Weawi..61c..32M |s2cid=194035906 }} so the time offsets are commonly understood as UTC.{{cite news |last1=Leigh |first1=Gabriel |title=Zulu and UTC: the story behind aviation's time zone |url=https://www.flightradar24.com/blog/zulu-and-utc-the-story-behind-aviations-time-zone/ |work=Flightradar24 Blog |date=17 November 2020}}{{cite web |title=Military Time Zones |url=https://veteran.com/military-time/ |website=Veteran.com |date=31 October 2022}}

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.{{cite news |last1=Stromberg |first1=Joseph |title=Sandford Fleming Sets the World's Clock |url=https://www.smithsonianmag.com/smithsonian-institution/sandford-fleming-sets-the-worlds-clock-389930/ |work=Smithsonian Magazine |date=November 18, 2011 |language=en|quote=To this day, if you look at certain [military] maps that divide the world into time zones, the zones are assigned letters,}}

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".{{cite report |author=Principal Staff Officers Committee|date=1950-06-15 |title=SG 037: Method of expressing date and time in military messages |url=https://archives.nato.int/method-of-expressing-date-and-time-in-military-messages |publisher=NATO Archives Online}} The British used a system of lettered zones, which was likely the direct influence.{{cite web |title=Time Zones for Earhart Radio Message Database |url=https://tighar.org/Publications/Books/FindingAmeliaNotes/JacobsonDatabase/RADIOMES/TIMEZONE.PDF |website=Finding Amelia Resource Library |access-date=2 June 2023}}{{bsn|date=June 2023}}

RFC 733 published in 1977 allowed using military time zones in the {{mono|Date:}} field of emails.{{cite web |title=Standard for the format of ARPA network text messages |url=https://datatracker.ietf.org/doc/html/rfc733#appendix-E |publisher=Internet Engineering Task Force |date=November 1977}} 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),{{cite web |last1=Braden |first1=Robert T. |title=Requirements for Internet Hosts - Application and Support |url=https://datatracker.ietf.org/doc/html/rfc1123#page-56 |publisher=Internet Engineering Task Force |date=October 1989}} 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.{{cite web |last1=Resnick |first1=Pete |title=Internet Message Format |url=https://datatracker.ietf.org/doc/html/rfc2822 |publisher=Internet Engineering Task Force |date=1 April 2001}}

• Lists of time zones
• Time zone abolition

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• [http://mm.icann.org/pipermail/tz/2009-January/015384.html "Military" time zones] discussion on the tz mailing list
• [http://www.timeanddate.com/library/abbreviations/timezones/military/ Military/NATO/Letter time zones]

{{UTC time offsets}}

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Category:Military terminology