How Military Time is Measured
The fundamental means of measuring time is the rotation of the earth. The original standard by which all clocks are regulated is furnished from observation of the stars and their relationship to the earth.
The primary unit of time is the "mean solar day." A mean solar day is the average of the "true solar day," which varies slightly in length. There are four times a year the mean and true solar days are equal, by contrast there are also days which time could vary as much as 16 or more minutes. The difference between the mean solar time and true solar time is called the "equation of time."
Whether telling the time via the direct observation of the stars or some other means, precision is paramount to the military. For the precision required in navigation and the syncing of mission resources of today's armed forces, everyone must be on the same page.
Enter, the atomic clock and the use of "Greenwich Mean Time."
For today's military, time pieces are calibrated using an atomic clock. The Department of Defense's main atomic clock that is used for calibration and to standardize time for the military was developed at the National Institute of Standards and Technology laboratories in Boulder, Colorado.
Military Time Zones
Every meridian has its own mean solar time. In order to avoid continual changing of time as one travels east or west standard time zones are introduced. Each time zone is 15 degrees of longitude in width. The difference between adjoining zones is one hour.
Nautical time zones are used by the military to ensure a standardization of time for the forces. Standard military orders would be delivered in Zulu time. Zulu time is the same as "Greenwich Mean Time" or GMT. Depending on the ship or units location on the planet, it will determine the amount of offset required. For example, if the orders were to launch a mission at 1000 Zulu, and your ship was located near Tokyo, Japan in the "India" time zone -- the India time zone is GMT plus nine hours, so you would subtract nine hours from 1000 Zulu, and know your time to launch would be 0100 local time (India).
Time Zone Chart
|Time Zone||Time Offset||Major City|
|A (Alpha)||GMT +1||Paris, France|
|B (Bravo)||GMT +2||Athens, Greece|
|C (Charlie)||GMT +3||Moscow, Russia|
|D (Delta)||GMT +4||Kabul, Afghanistan¹|
|E (Echo)||GMT +5||New Delhi, India|
|F (Foxtrot)||GMT +6||Dhaka, Bangladesh|
|G (Golf)||GMT +7||Bangkok, Thailand|
|H (Hotel)||GMT +8||Beijing, China|
|I (India)||GMT +9||Tokyo, Japan|
|K (Kilo)||GMT +10||Sidney, Australia|
|L (Lima)||GMT +11||Honiara, Solomon Islands|
|M (Mike)||GMT +12||Wellington, New Zealand|
|N (November)||GMT -1||Ponta Delgada, Azores|
|O (Oscar)||GMT -2||Godthaab, Greenland|
|P (Papa)||GMT -3||Buenos Aires, Argentina|
|Q (Quebec)||GMT -4||Halifax, Nova Scotia|
|R (Romeo)||GMT -5||New York, NY United States|
|S (Sierra)||GMT -6||Dallas, TX United States|
|T (Tango)||GMT -7||Denver, CO United States|
|U (Uniform)||GMT -8||Los Angeles, CA United States|
|V (Victor)||GMT -9||Juneau, AK United States|
|W (Whiskey)||GMT -10||Honolulu, HI United States|
|X (X-Ray)||GMT -11||Nome, AK United States|
|Y (Yankee)||GMT -12||Suva, Fiji|
|Z (Zulu)||GMT||Greenwich, England|
Note 1: Although located in the Delta Time Zone, local time in Afghanistan is GMT +4 hours 30 minutes.
Note 2: Although not normally utilized in military communication due to the confusion it can cause, the time zone J (Juliet) has be used to indicate the observer's local time in other forums.
Military Time Conversion
The United States military uses a 24 hour clock to save confusion. There are not two "four o'clocks" in military time as there is with civilian time. The civilian 4:00AM is equal to 0400 (Zero four hundred) and 4:00PM is equal to 1600 (Sixteen hundred) military time.
A couple more examples of local time conversion and how to speak it: if local time is 9:27 AM, the local military time would be 0927, and it would be spoken as "Zero nine twenty seven." If the local time was 7:36 PM, the local military time would be 1936, and it would be spoken as "Nineteen thirty six."
Civilian to Military Time Conversion Chart
|Military Time||Standard Time||Military Time||Standard Time|
|0100||1 AM||1300||1 PM|
|0200||2 AM||1400||2 PM|
|0300||3 AM||1500||3 PM|
|0400||4 AM||1600||4 PM|
|0500||5 AM||1700||5 PM|
|0600||6 AM||1800||6 PM|
|0700||7 AM||1900||7 PM|
|0800||8 AM||2000||8 PM|
|0900||9 AM||2100||9 PM|
|1000||10 AM||2200||10 PM|
|1100||11 AM||2300||11 PM|
Reading The Message Traffic "Day Time Group"
When message traffic is sent, each message receives a Day Time Group (DTG). The DTG has the day, month, year and time the message is logged. For example, a message's DTG may say, 212200Z May 2013. Broken down, you know the message was logged on May 21, 2013 at 2200 Zulu time.
Written by NCCM Thomas Goering USN (RET).
Article published on September 22, 2015.
Article modified on June 18, 2019.