The military uses a 24-hour clock system to avoid confusion and ambiguity in time notation. Hours start at 0000 and increase by 100, with minutes replacing the last 00. The military watch follows the local time zone, except for international transactions where Greenwich Mean Time (GMT) is used with the letter Z indicating the Zulu time zone.
The civilian world generally uses a 12-hour clock system, meaning that the same time notation is displayed twice a day, followed by an AM or PM designation. Asking a friend to meet you for dinner at 7:30 may seem logical, but not giving 7:30 could be confusing. The military can’t risk causing confusion in the ranks, so they prefer to use a 24-hour clock to eliminate any ambiguity in time notation.
Military time is divided into hours, starting at 0000 hours at midnight. From that starting point, the hours increase by 100. For example, 1 or 1 in the morning in civil time would be rendered as 0100 or 0100 hours in military time. This pattern continues at 0200 hours, 0300 hours, 0400 and so on. The minutes after the hour would be rendered in place of the last 00. 2:45 am would be 0245 in military time and 7:45 would become 0745.
Noon or 12:00 becomes 1200 hours in military time, and this is where the 24-hour clock notation becomes most apparent. 1:00 becomes 1300 hours in military time and the pattern of adding to a base of 1200 hours begins. 2am becomes 1400, followed by 1500 (3:2300) and so on until 1345:0145. The same rules apply to minutes during the afternoon and night hours. A mission can start at XNUMX:XNUMX, for example. This would read “thirteen hundred and forty-five hours”, which would immediately distinguish it from XNUMX hours.
The military watch generally follows the local time zone of the installation location, including DST adjustments when required. This may require some calculations if a military base in California is coordinating an operation with a base in Florida. For most events, the military time shown is in the local time zone, so 1345 hours in California may equal 1645 hours at an East Coast base.
An exception to this rule is for international transactions. Because the world is divided into numerous time zones, the military generally uses Greenwich Mean Time (GMT) to coordinate mission times across different time zones. Since Greenwich, England is in the Z or Zulu time zone, it is not unusual to see the letter Z placed at the end of the 24-hour clock notation. Therefore, a mission scheduled to start at 1400 Z would depart at 00 Z 00 local time in Greenwich, England. This “Zulu time” notation is designed to ensure that all military personnel begin an operation at exactly the same time.