The History of Military Time

The military uses a 24-hour clock to keep track of time. Keep reading to learn all about the fascinating history of military time.

Military Time Overview

Military time uses a 24-hour clock while civilian time uses a 12-hour clock.

Because military time also uses different notations than civilian time, people need to familiarize themselves with that notation style to understand and use military time.

Military Time Chart:

• 0100 (zero one hundred hours)
• 0200 (zero two hundred hours)
• 0300 (zero three hundred hours)
• 0400 (zero four hundred hours)
• 0500 (zero five hundred hours)
• 0600 (zero six hundred hours)
• 0700 (zero seven hundred hours)
• 0800 (zero eight hundred hours)
• 0900 (zero nine hundred hours)
• 1000 (ten hundred hours)
• 1100 (eleven hundred hours)
• 1200 (twelve hundred hours)
• 1300 (thirteen hundred hours)
• 1400 (fourteen hundred hours)
• 1500 (fifteen hundred hours)
• 1600 (sixteen hundred hours)
• 1700 (seventeen hundred hours)
• 1800 (eighteen hundred hours)
• 1900 (nineteen hundred hours)
• 2000 (twenty hundred hours)
• 2100 (twenty-one hundred hours)
• 2200 (twenty-two hundred hours)
• 2300 (twenty-three hundred hours)
• 2400 or 0000 (twenty-four hundred hours or zero hundred hours)

Example

If it’s 4:13 p.m. in civilian time , that’s 1613 (sixteen hundred thirteen hours) in military time.

Military Time Conversion

To convert military time back to civilian time, simply subtract 12 from any numbers after noon (1200). That will give you the equivalent p.m. time. 

Military time conversion is so easy you don’t need a military time converter. You can do it in your head.

Example

To convert 1600 military time to civilian time, subtract 12 from 16 to get 4. That means it’s 4 p.m. in civilian time.

What time is it in military time? Add 12 to all times after noon. If you add 12 to 4 p.m., you get 16. That means it’s 1600 military time.

The Egyptian’s 24-Hour Clock

In 2100 B.C.E., Egyptians notated decans on coffin lids. Decans consist of 36 small constellations that  ancient Egyptians used to measure time at night when they could no longer use the sun. 

Every 10 days, one of these constellations helically rose in prominence to give the ancient Egyptians a 10-day week.  A year comprised 36 weeks for each of the 36 constellations. To balance out the seasons, the ancient Egyptians added five extra days each year to create a 365-day year.

The Egyptians measured night and day independently. During the day, they used the sun to measure time. At night, they used the stars. This means the Egyptians used two separate clocks, dividing day and night into two disproportionate parts. Their timekeeping has strong similarities to the proportionate, 12-hour clock used today, which we divide into ante meridiem (a.m.) and post meridiem (p.m.) to indicate times before and after midday.

The Egyptians later combined night and day into equal parts measured in hours, which created the first 24-hour clock.

The Military’s Use of a 24-Hour Clock

In 1914, the United Kingdom’s Royal Navy adopted the 24-hour clock. This marked the first time a military organization used a 24-hour clock to measure time.

Military Adoption of the 24-Hour Clock:

• 1914: The United Kingdom’s Royal Navy
• 1917: The Canadian Armed Forces
• 1918: The British Army
• 1920: The U.S. Navy
• 1942: The U.S. Army

Expand Your Knowledge of Military Time

Want to know more about military time? Read on for  more useful information.

Military Time Facts:

• The military uses the Military Alphabet to name time zones. For example, Zulu Time is the same as Coordinated Universal Time (UTC) and Greenwich Mean Time (GMT).
• People indicate military time zones with a single letter following the time. For example, 0600R stands for zero six hundred Romeo Time. That translates to -5 UTC or Eastern Standard Time (EST).
• Military time uses Daylight Savings Time (DST) in  countries that recognize DST. For example, Romeo Time, when used in New York City, will gain an hour in spring and lose an hour in autumn.
• Military time helps prevent confusion with a.m. and p.m. times in high-risk organizations like the news media, hospitals, commercial aviation companies, the military, and other emergency organizations.
• Other names for military time include Aviation Time, and NATO Time.

Frequently Asked Questions

What countries use 24-hour time?

European countries commonly set digital clocks to a 24-hour clock. In conversation, especially in French-speaking countries, saying “16” or “16 hundred” to refer to 4 p.m. is quite common.

Many Asian countries, particularly China, also use a 24-hour clock when referring to time schedules and transportation timings.

Is 24 hours a day?

Generally speaking, yes, a solar day has 24 hours. But, a day can last a few minutes longer or shorter than 24 hours because the Earth isn’t a perfect circle.

A solar day measures the time it takes for the Earth to rotate on its axis until the sun appears again in the same position. In contrast, a sidereal day measures the time it takes the Earth to rotate on its axis in reference to a star’s position in space. A sidereal day lasts 23 hours, 56 minutes, and 4.09 seconds.

Is it 2400 or 0000?

Military time uses both 2400 and 0000 to notate midnight. This may seem confusing at first, but it makes more sense if you think of 0000 as a start time and 2400 as an end time. You’d use 0000 when referencing the beginning of an activity, but 2400 to indicate when an activity will end. 

If you plan to wake up at midnight, for example, you’d say, “I’m getting up at zero hundred hours (0000).” If you plan to go to bed at midnight, you’d say, “I’m going to bed at 24-hundred hours (2400).”

How do you convert military time to civilian time?

You can convert military time to civilian time for numbers after noon by subtracting 12 from the number. For example, if it’s 1800 hours in military time, you’d subtract 12 from 18 and get six. That means it’s 6 p.m. in civilian time.

To convert civilian time to military time, simply add 12 to numbers after noon. For example, if it’s 7 p.m. in civilian time, you’d add 12 to get 19. That means it’s 1900 hours in military time.

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