With military operations conducted across the globe, the military clarifies time further by appending the time zone with a letter of the NATO phonetic alphabet. The way this works is the military divided the world into 24 time zones and assigned a letter of the phonetic alphabet to each time zone.

To avoid confusion in these matters, the military uses the time in Greenwich, England, which is commonly called Greenwich Mean Time. However, the U.S. Military refers to this time zone as Zulu time. The 'zulu' comes from the fact that each time zone is given a letter designation, 'z' being the 24th.

When it is noon in the Eastern time zone, it is 11 a.m. in the Central time zone, 10 a.m. in the Mountain time zone and 9 a.m. in the Pacific time zone. All time zones are measured from a starting point centered at England's Greenwich Observatory. This point is known as the Greenwich Meridian or the Prime Meridian.

On November 18, 1883, America's railroads began using a standard time system involving four time zones, Eastern, Central, Mountain and Pacific. Within each zone, all clocks were synchronized.