<P> In American and Canadian English, the term military time is a synonym for the 24 - hour clock . In these dialects, the time of day is customarily given almost exclusively using the 12 - hour clock notation, which counts the hours of the day as 12, 1,..., 11 with suffixes a.m. and p.m. distinguishing the two diurnal repetitions of this sequence . The 24 - hour clock is commonly used there only in some specialist areas (military, aviation, navigation, tourism, meteorology, astronomy, computing, logistics, emergency services, hospitals), where the ambiguities of the 12 - hour notation are deemed too inconvenient, cumbersome, or dangerous . </P> <P> Military usage, as agreed between the United States and allied English - speaking military forces, differs in some respects from other twenty - four - hour time systems: </P> <Ul> <Li> No hours / minutes separator is used when writing the time, and a letter designating the time zone is appended (for example "0340Z"). </Li> <Li> Leading zeros are always written out and are required to be spoken, so 5: 43 a.m. is spoken "zero five forty - three" (casually) or "zero five four three" (military radio), as opposed to "five forty - three" or "five four three". </Li> <Li> Military time zones are lettered and thus given word designations via the NATO phonetic alphabet . For example, 6: 00 a.m. US Eastern Standard Time (UTC − 5) would be written "0600R" and spoken "zero six hundred Romeo". </Li> <Li> Local time is designated as zone J or "Juliett". "1200J" ("twelve hundred Juliett") is noon local time . </Li> <Li> Greenwich Mean Time (or Coordinated Universal Time) is designated time zone Z, and thus called "Zulu time". </Li> <Li> Hours are always "hundred", never "thousand"; 1000 is "ten hundred" not "one thousand"; 2000 is "twenty hundred" not "two thousand". </Li> </Ul> <Li> No hours / minutes separator is used when writing the time, and a letter designating the time zone is appended (for example "0340Z"). </Li>

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