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. The CCEB, representing the armed forces of Australia, Canada, New Zealand, the United Kingdom, and the United States, publishes the military time zone system as the ACP 121 standard. [1] The armed forces of Austria and many nations in NATO use it.[ citation needed ]
Going east from the prime meridian at Greenwich, letters "Alfa" [lower-alpha 1] 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 name | Degrees longitude | Designation letter | Zone description | Offset |
---|---|---|---|---|
Alfa [lower-alpha 1] 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 [lower-alpha 2] | 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 [lower-alpha 3] | 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' was previously misidentified in some editions of U.S. Army publications, such as FM 5-0, [3] 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, [4] which no longer includes this incorrect usage. "LT" may also (rarely) be used to denote local time. [5]
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, [6] so the time offsets are commonly understood as UTC. [7] [8]
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. [9]
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". [10] The British used a system of lettered zones, which was likely the direct influence. [11] [ better source needed ]
RFC 733 published in 1977 allowed using military time zones in the Date: field of emails. [12] 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), [13] 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. [14]
Greenwich Mean Time (GMT) is the local mean time at the Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, including being calculated from noon; as a consequence, it cannot be used to specify a particular time unless a context is given. The term "GMT" is also used as one of the names for the time zone UTC+00:00 and, in UK law, is the basis for civil time in the United Kingdom.
ISO 8601 is an international standard covering the worldwide exchange and communication of date and time-related data. It is maintained by the International Organization for Standardization (ISO) and was first published in 1988, with updates in 1991, 2000, 2004, and 2019, and an amendment in 2022. The standard provides a well-defined, unambiguous method of representing calendar dates and times in worldwide communications, especially to avoid misinterpreting numeric dates and times when such data is transferred between countries with different conventions for writing numeric dates and times.
A time zone is an area which observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time.
In communications messages, a date-time group (DTG) is a set of characters, usually in a prescribed format, used to express the year, the month, the day of the month, the hour of the day, the minute of the hour, and the time zone, if different from Coordinated Universal Time (UTC). The order in which these elements are presented may vary. The DTG is usually placed in the header of the message. One example is "20:13 Jun 12, 2024 (UTC)"; while another example is "20:13 12 Jun 2024".
Universal Time is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle. UT1 is the same everywhere on Earth. UT1 is required to follow the relationship
The International Meridian Conference was a conference held in October 1884 in Washington, D.C., in the United States, to determine a prime meridian for international use. The conference was held at the request of U.S. President Chester A. Arthur. The subject to discuss was the choice of "a meridian to be employed as a common zero of longitude and standard of time reckoning throughout the world". It resulted in the recommendation of the Greenwich Meridian as the international standard for zero degrees longitude.
The Allied military phonetic spelling alphabets prescribed the words that are used to represent each letter of the alphabet, when spelling other words out loud, letter-by-letter, and how the spelling words should be pronounced for use by the Allies of World War II. They are not a "phonetic alphabet" in the sense in which that term is used in phonetics, i.e. they are not a system for transcribing speech sounds.
The modern 24-hour clock is the convention of timekeeping in which the day runs from midnight to midnight and is divided into 24 hours. This is indicated by the hours passed since midnight, from 00(:00) to 23(:59), with 24(:00) as an option to indicate the end of the day. This system, as opposed to the 12-hour clock, is the most commonly used time notation in the world today, and is used by the international standard ISO 8601.
In the United States, time is divided into nine standard time zones covering the states, territories and other US possessions, with most of the country observing daylight saving time (DST) for approximately the spring, summer, and fall months. The time zone boundaries and DST observance are regulated by the Department of Transportation, but no single map of those existed until the agency announced intentions to make one in September 2022. Official and highly precise timekeeping services (clocks) are provided by two federal agencies: the National Institute of Standards and Technology (NIST) ; and the United States Naval Observatory (USNO). The clocks run by these services are kept synchronized with each other as well as with those of other international timekeeping organizations.
Standard time is the synchronization of clocks within a geographical region to a single time standard, rather than a local mean time standard. Generally, standard time agrees with the local mean time at some meridian that passes through the region, often near the centre of the region. Historically, standard time was established during the 19th century to aid weather forecasting and train travel. Applied globally in the 20th century, the geographical regions became time zones. The standard time in each time zone has come to be defined as an offset from Universal Time. A further offset is applied for part of the year in regions with daylight saving time.
In modern usage, civil time refers to statutory time as designated by civilian authorities. Modern civil time is generally national standard time in a time zone at a fixed offset from Coordinated Universal Time (UTC), possibly adjusted by daylight saving time during part of the year. UTC is calculated by reference to atomic clocks and was adopted in 1972. Older systems use telescope observations.
South African Standard Time (SAST) is the time zone used by all of South Africa as well as Eswatini and Lesotho. The zone is two hours ahead of UTC (UTC+02:00) and is the same as Central Africa Time. Daylight saving time is not observed in either time zone. Solar noon in this time zone occurs at 30° E in SAST, effectively making Pietermaritzburg at the correct solar noon point, with Johannesburg and Pretoria slightly west at 28° E and Durban slightly east at 31° E. Thus, most of South Africa's population experience true solar noon at approximately 12:00 daily.
Time in Chile is divided into three time zones. Most of Continental Chile uses the time offset UTC−04:00 in winter time and UTC−03:00 in summer time, while the Magallanes and Chilean Antarctica region uses the time offset UTC−03:00 the whole year. Additionally, Easter Island uses the time offset UTC−06:00 in winter time and UTC−05:00 in summer time.
UTC+00:00 is an identifier for a time offset from UTC of +00:00. This time zone is the basis of Coordinated Universal Time (UTC) and all other time zones are based on it. In ISO 8601, an example of the associated time would be written as 2069-01-01T12:12:34+00:00. It is also known by the following geographical or historical names:
Nautical time is a maritime time standard established in the 1920s to allow ships on high seas to coordinate their local time with other ships, consistent with a long nautical tradition of accurate celestial navigation. Nautical time divides the globe into 24 nautical time zones with hourly clock offsets, spaced at 15 degrees by longitudinal coordinate, with no political deviation.
Venezuela uses the UTC−04:00 time offset, and they had previously used UTC−04:30 from 9 December 2007 until 30 April 2016. The time is commonly called Venezuelan Standard Time (VET), and legally referred to as Hora Legal de Venezuela (HLV) or Venezuela's Legal Time. The HLV is administered by the Navigation and Hydrography Service, in the Cagigal Naval Observatory, Caracas.
Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communication, navigation, scientific research, and commerce.
Denmark, including its dependencies of Faroe Islands and Greenland, uses six time zones.
Time in Liberia is given by a single time zone, denoted as Greenwich Mean Time. Liberia shares this time zone with several other countries, including fourteen in western Africa where it was formerly known as Western Sahara Standard Time (WSST). Liberia has never observed daylight saving time (DST).
Nigeria observes West Africa Time (WAT), which is one hour ahead of Coordinated Universal Time (UTC+01:00), year-round as standard time. Nigeria has never observed daylight saving time. It shares WAT with fourteen other countries in Africa. Nigeria's local mean time was UTC+00:13:35.
Express all times in a plan or order in terms of one time zone, for example ZULU (Z) or LOCAL (L). I
'LT A120 T1540' = 'Your bearing from me is 120° at (local time) 1540'.
To this day, if you look at certain [military] maps that divide the world into time zones, the zones are assigned letters,