24-hour Clock - Military Time

Military Time

In Canada and the United States, the term "military time" is a synonym for the 24-hour clock. In these regions, 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 outright dangerous, with the military's use being the most famous example. The term "military time" has no particular meaning in most other regions of the world, where the 24-hour clock has long become a common element of everyday civilian life.

In the United States military, military time is similar to the 24-hour clock notation, with the exception that the colon is omitted and the time on the hours is often spoken as its decimal value. For instance, 6:00 a.m. would become 0600, and would be spoken "zero six hundred" or "zero six hundred hours" (for example, when said face-to-face), "oh six hundred" (colloquial and not strictly correct, as military communication protocols specify the word "zero" rather than "oh"), or "zero six zero zero" (for example, where clarity is needed when specifying the time over a radio or sound-powered telephone). Hours are always "hundred", never "thousand"; 10:00 is "ten hundred" not "one thousand", 20:00 is "twenty hundred". However, none of these formatting or pronunciation details is exclusively military and all are common in the technical contexts in which the 24-hour clock is used in English-speaking countries.

Military usage differs in some respects from other twenty-four-hour time systems:

• Written military time does not usually include a time separator (for example, "0340" is more common than the civilian "03:40").
• Leading zeros, always written out by the military, are often also spoken in military usage, so 5:43 a.m. is often spoken "zero five forty-three" (military), as opposed to "five forty-three" (civilian).
• Military time zones are lettered and thus given word designations via the NATO phonetic alphabet. For example, 6:00AM Eastern Standard Time (GMT-5) would be written "0600R" and spoken, "zero six hundred Romeo".
• Local time is specifically designated in the military as zone J or "Juliet". A time of "1200J" ("twelve hundred Juliet") corresponds to noon local time.
• Greenwich Mean Time (or Coordinated Universal Time) is designated as zone Z or "Zulu". Usage of Z time is common in operations crossing multiple time zones.