Military 24hr Time

U.S. Navy rescue swimmers Senior Chief John Wandke and Apprentice Rogelio Govea from the HH-60 Black Knights helicopter squadron synchronize their watches before a search and rescue activity in support of exercise Northern Edge 2002, 25 April 2002
U.S. Navy rescue swimmers Senior Chief John Wandke and Apprentice Rogelio Govea from the HH-60 Black Knights helicopter squadron synchronize their watches before a search and rescue activity in support of exercise Northern Edge 2002, 25 April 2002.

Today in WW II: 22 Sep 1943 Operation TOENAILS completed, with the occupation by US troops of all important islands in the New Georgia group, Central Solomons.  

Military Time is Zulu Time

For scientific reasons based on increased accuracy in measuring the earth's rotation, a new timescale, called Coordinated Universal Time (UTC), was adopted 1 January 1972. UTC replaces the previous term GMT (for Greenwich Mean Time). UTC refers to each of the world's time zones as being plus time or minus time from the Prime Meridian (Longitude Zero) that passes through the Royal Greenwich Observatory, in Greenwich, England, southeast of central London. For example, New York City is located in the U.S. Eastern Standard Time (EST) zone which is UTC minus 5 hours.

The U.S. military, as well as NASA, civil aviation and others, use the letter "Z" (phonetically "Zulu") to refer to the time at the Prime Meridian. Since the military has to coordinate operations on a world-wide basis, "Zulu Time" is used at all locations.

The Department of the Navy serves as the official timekeeper for the U.S. Department of Defense as well as for the Global Positioning System (GPS) utilizing the Master Clock at the Time Service Department, U.S. Naval Observatory, Washington, DC.

Military 24 Hour Time

The military 24 hour clock system
The military 24 hour clock system.

The military expresses time based on a 24 hour clock, not the conventional twelve hour clock utilized by American civilians and in some other regions. There is no AM or PM, just a four digit time that can express any minute of the day. The first two numbers are the hour and the last two are the minute. Here is how it works for some example times of the day (see clock above):

Civilian Time Military Time How Spoken
Midnight 2400 twenty-four hundred
1 minute after midnight 0001 zero-zero-zero-one or zero-oh-one
30 minutes after midnight 0030 zero-zero-30
2:00 AM 0200 zero-two hundred
11:59AM 1159 eleven fifty-nine
Noon 1200 twelve hundred
2:00PM 1400 fourteen hundred
5:30PM 1730 seventeen thirty
11:00PM 2300 twenty-three hundred
11:59PM 2359 twenty-three fifty-nine

There are many small variations of this basic system, depending on location, service branch customs, and special needs.

The word "hours" is sometimes added to the time, e.g. "seventeen thirty hours" a form that was more common in the past. Zero may be spoken as "oh". On radio transmissions, typically all numbers will be spoken to increase clarity, e.g. "one-seven-three-zero hours" for 5:30PM.

Midnight is equally 0000 and 2400 (zero-zero-zero-zero or twenty-four hundred). In most circumstances you would use 0000 for the beginning of an interval (Duty starts at 0000!) while using 2400 for the end of an interval (Remain here until 2400!).

Terminology such as zero-dark-30 (or oh-dark-30) and the like is informal, indicating a time after midnight when you would rather be sleeping (We have to move out at oh-dark-30).

Military Date Format

The military uses a specific format for dates, again to eliminate any possible confusion or misinterpretation. The date format is in three parts:

  • The day of the month
  • The month name, often abbreviated to three capitalized letters
  • The year using the last two digits or four digits if the month is spelled out in full

As an example, September 4, 2005 would be expressed as 4 September 2005 or 4 SEP 05. The month abbreviation is always the first three letters of the month, usually capitalized. Most dates on Olive-Drab.com follow the military style.

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