The military operates off a 24-hour clock, beginning at midnight (which is 0000 hours). So, 1:00 AM is 0100 hours, 2:00 AM is 0200 hours, and so-on up until 11:00 PM which is 2300 hours.
Here's the whole list:
Midnight (12:00 AM) -- 0000 hrs
1:00 AM -- 0100 hrs
2:00 AM -- 0200 hrs
3:00 AM -- 0300 hrs
4:00 AM -- 0400 hrs
5:00 AM -- 0500 hrs
6:00 AM -- 0600 hrs
7:00 AM -- 0700 hrs
8:00 AM -- 0800 hrs
9:00 AM -- 0900 hrs
10:00 AM -- 1000 hrs
11:00 AM -- 1100 hrs
12:00 PM -- 1200 hrs
1:00 PM -- 1300 hrs
2:00 PM -- 1400 hrs
3:00 PM -- 1500 hrs
4:00 PM -- 1600 hrs
5:00 PM -- 1700 hrs
6:00 PM -- 1800 hrs
7:00 PM -- 1900 hrs
8:00 PM -- 2000 hrs
9:00 PM -- 2100 hrs
10:00 PM -- 2200 hrs
11:00 PM -- 2300 hrs
For most daily things, military personnel use local time as a reference. In order words, "report to duty at 0700," would mean you have to be at work at 7:00 AM, local time. "The Commander wants to see you at 1500 hrs," means you need to be in the Commander's office at 3:00 PM, local time.
When using local time, the Military observes Daylight Savings Time, if recognized by the state or country that the base is located in.
When it comes to operational matters (such as communications, training exercises, deployments, ship movements aircraft flights, etc.), the military must often coordinate with bases and personnel located in other time zones. To avoid confusion, in these matters, the military uses the time in Greenwich, England, which is commonly called Greenwich Mean Time (GMT). However, the U.S. Military refers to this time zone as Zulu Time, and they attach the "Zulu" (Z) suffix, to ensure the time-zone referred to is clear.
For example, a military message or communication might state, "The ship will cross into the area of operations at 1300Z." That means the ship would arrive in the AOO when it is 1:00 PM in Greenwich, England.
Why does the military call this time "Zulu Time?" The world is divided into basically 24 time zones. For easy reference in communications, a letter of the alphabet has been assigned to each time zone. The time zone for Greenwich, England has been assigned the letter "Z." The Military phonetic alphabet for the letter "Z" is "Zulu."
