Most of us in the United States know that the military time clock differs from standard civilian time. Some are familiar with the differences because they either serve in the military or are part of a military family. Others recognize the parlance from pop culture, perhaps a movie or television program such as M.A.S.H. Simply put, military time refers to a 24-hour system of time.
What many of us don’t realize is that while the 24-hour clock is used by the military, it is used in some streams of civilian life, too. This includes law enforcement, firefighters, emergency medical staff, pilots, meteorologists, and astrologists. Military time is also commonly used in railway tables and legal contracts.
The 24-hour system of telling time began long before the United States military adopted it. It was in 2100 B.C. that Egyptians began organizing time according to the patterns they observed in constellations. Though hours were not yet 60-minute segments, a day was organized into 24-hour chunks. After various adaptations and alterations, the United States Navy began using the 24-hour system in 1920. The U.S. army followed in 1942. To learn more about the history of military time, read here.
The Purpose of Military Time
What is the purpose of using a system of time different from that of most civilians (at least in the United States)? Most who use it would probably say it is more clear and consistent. It decreases mistakes. Those who have missed their wake-up alarm because it has been accidentally set for p.m. rather than a.m. likely understand. It is often used in situations requiring precision. In hospitals, for instance, patients often need to be given medicine at specific times of the day. While 0800 hours refers to only one specific time, if the a.m. or p.m. is inadvertently dropped, 8:00 refers to two. Reducing room for error is important in a medical environment where a simple mistake can have devastating consequences.
Military time is also used by those who live and work in polar climates. Because the sun’s appearance is either much longer during a single day or much shorter, confusion over time is more likely with a repetitive 12-hour system of time.
And of course, precision is necessary in the military. Because bases and personnel are located all over the globe and in different time zones, any type of standardized, simplified system of time is desirable.
Military Time in a Nutshell
Military time uses two double-digit numbers. The first number begins at 00 and runs through 24. It refers to the hour of the day. The second number begins at 00 and runs through 60. It refers to minutes in an hour. Sometimes a third set is used, also 0 to 60, and refers to the seconds in a minute.
Each day is broken into 24-hour segments ( the first double-digit number) beginning at midnight. For example, 00 refers to midnight, 01 refers to 1 a.m., and so on. Following noon or 12 p.m., the numbers might become unfamiliar to a civilian. The hour of 1 p.m. is designated as 13; the hour of 2 p.m. is designated as 14 and so on. Midnight is correctly referred to as either 2400 or 0000. Digital clocks/watches and computers always refer to it as 0000.
The time is often given in hours and minutes with no punctuation between the two. The word “hours” usually follows. For example, the civilian standard time 10:10 a.m. would be referred to as 1010 hours in military time. When seconds are used, a colon is included after the minutes. For example, 10:10 a.m.
+ 20 seconds refers to 1010:20 hours in military time. Some groups may differ slightly in their usage. For example, science and engineering groups often use a colon between hours, minutes, and seconds. In the above example they would refer to the time as 10:10:20 hours.
Military time is also expressed in regard to a particular time zone. In so doing, it makes clear the time in a particular place. The globe is split into 24 military time zones, each assigned a military phonetic word and corresponding initial letter. An example of this is Greenwich Mean Time (GMT) which the military uses as the standard in order to synchronize personnel across many time zones. The military calls this Zulu time and its corresponding letter is Z. Therefore, 6 p.m. Zulu time is written as 1800z in military time. It is spoken as “eighteen hundred hours Zulu time.”
Sometimes time is expressed locally. The phonetic word that indicates local time is Juliet and the corresponding letter is J. Thus, 6 p.m. local time is written as 1800J. It is spoken as “eighteen hundred hours Juliet time.” Read more about military time and time zones here.
Differences Between Military and Standard Time
While the hours are denoted differently in military and standard time, the minutes and seconds are denoted the same way. Standard time denotes hours by the numbers 1 through 12 which are repeated twice during a 24-hour day. Military time, on the other hand, denotes hours by the numbers 00 through 23 or 24. (Midnight is accurately referred to as either 2400 or 0000.) Minutes and seconds are denoted by the numbers 00 through 60 in both military and standard time.
One other difference is the words that follow the time. In standard time, the initials a.m. (from the Latin ante meridiem meaning before midday) and p.m. (from the Latin post meridiem meaning after midday) follow the time and indicate whether the first group of 12 hours is being referred to or the second. In military time, the word “hours” always follows the time. Sometimes the time zone is also written after the word “hours.” Each time zone on the globe has a designated name and letter of abbreviation. For example, Greenwich Mean Time (GMT) is referred to as Z. The civilian time 10:10 a.m. might be written as 1010Z.
Speaking in Military Time
Because in math class we learn that the number 03 is equal to 3, it is tempting to drop the 0 when giving the time. However, in military time, the 0 is always read as part of the time. For instance, 0300 hours would be pronounced “zero three hundred hours” or “oh three hundred hours.”
Converting from Military Time to Standard Time
For a time 1200 hours or earlier, first, add a colon between the hour and minutes. Next, drop the 0 if it begins the time. Finally, add a.m. at the end. The time 0930 hours becomes 9:30 a.m.
For a time later than 1200 hours, first subtract 12 from the hours. Next, add p.m. at the end. The time 1630 hours becomes 4:30 p.m.
Converting from Standard Time to Military Time
If the time is 11:59 a.m. or earlier, eliminate both the colon and the a.m. Next, add the word “hours.” Also, if the hour is a single digit, add a 0 before it. The time 8:25 a.m. becomes 0825 hours.
If the time is 12:00 p.m. or later, add 12 hours to the time. Next, eliminate p.m. at the end and add the word “hours.” The time 3:55 p.m. becomes 1555 hours.
For those who don’t like to do the math in their heads, the chart below will help move back and forth between the 12-hour system and 24-hour or military system.
0000 hours 12 a.m.
0100 hours 1 a.m.
0200 hours 2 a.m.
0300 hours 3 a.m.
0400 hours 4 a.m.
0500 hours 5 a.m.
0600 hours 6 a.m.
0700 hours 7 a.m.
0800 hours 8 a.m.
0900 hours 9 a.m.
1000 hours 10 a.m.
1100 hours 11 a.m.
1200 hours 12 a.m.
1300 hours 1 p.m.
1400 hours 2 p.m.
1500 hours 3 p.m.
1600 hours 4 p.m.
1700 hours 5 p.m.
1800 hours 6 p.m.
1900 hours 7 p.m.
2000 hours 8 p.m.
2100 hours 9 p.m.
2200 hours 10 p.m.
2300 hours 11 p.m.
Military Time Clocks
For those who use only the 24-hour system of time, both wall clocks and watches are available that designate the hours of the day beginning at 00 and going through 23. For those who use both the 12-hour and 24-hour systems, clocks and watches which show both are available. The numbers 1 through 12 ring the perimeter of the clock with numbers 00-23 inside on a smaller perimeter.
In places such as the United States or Great Britain, the 12-hour time system is the norm. However, in many non-English speaking countries the 24-hour time system or military time is used. It might be confusing to some to hear 8 a.m. referred to as “oh 8 hundred hours.” (Hundred hours? Why the “oh”?) However, the system is actually more precise and helps reduce mistakes. Whether in civilian or military life, the 24-hour system of time is favored around the world.