The invention of the 24-hour military clock, as you can read here, played an immediate and pivotal role in improving navigation at sea by implementing a standardized longitudinal time over variable local times. Greenwich Mean Time (GMT) was founded in 1675 but worldwide time zones would not be agreed upon or implemented for another 200 years.
Standardizing time zones became important for many with the introduction of nation-wide railway systems. Before this point, the mere concept of a layman crossing several time zones over land was incomprehensible. In the United States, the Intercontinental Railroad, which ran from San Francisco, CA to Omaha, NE, was completed in 1869 and is representative of the new era of travel that brought about the need for regulated time zones. Charles F. Dowd was the first to discuss regulated time zones in the US in 1863 but he only mentioned his thoughts to his students. His reason for wanting standardized times was similar to that of many others; he was never sure exactly what time the train would arrive or depart. He proposed his idea to a railroad committee in 1869, suggesting 15-degree longitudinal intervals between zones, all centered around Greenwich, England. The committee rejected every part of his proposal except for the idea to use Greenwich as a central point.
The committee instead went with an 1883 proposal by the William F. Allen, editor of the Travelers Official Railway Guide of the United States, Mexico and Canada, which suggested the use of major railroad stops as time zone borders. General Time Convention was officially implemented on November 18, 1883, a day that became known as “The Day of Two Noons.” On this day, all clocks were stopped and restarted at the exact same time so they would be in sync. Some people, therefore, experienced 12 pm twice in one day. Over time, the time zone borders were moved from the major railway stops to more rural areas to ease the transition for travelers.
Worldwide time zones were suggested by several individuals, including Quirico Filopanti of Italy and Sir Sanford Fleming of Scotland. By 1900, the majority of the world was broken up into 24 standardized time zones but it wasn’t until 1956, when Nepal adopted hourly time zones, that all countries had accepted the universal time zones we have today.
Converting Time Zones
Coordinated Universal Time (UTC), which was was formalized in 1960, is still based on Greenwich time, which can be denoted as UTC or UTC + 0. Each time zone also has a letter associated with it, as represented in the chart below.
UTC is in time zone “Z” on the chart, or Zulu time. To denote a different time zone using UTC, you can simply add or subtract by the number of time zones. For these conversions, we can use the chart below:
If, for example, I want to portray time in New York, I could denote it as UTC – 5 because the time in New York is five time zones behind UTC. I could also say I was in time zone Romeo. If I want to portray time in Egypt, I could write UTC + 2 because Egypt is two time zones ahead of UTC or I could use time zone Bravo. If, say, I was in New York and wanted to know the time in Greenwich (or UTC), I would just have to take my time and add five. So 1300, or 1 pm, in New York would be 1800, or 6 pm, in Greenwich. For any conversion from local time to UTC, simply change the plus to a minus (or vice versa) and add the associated number.
Some countries are split into several time zones because of their size and some, like China, encroach on adjacent time zones but stay in one zone (although China is such a large country that several areas choose to follow unofficial time zones that better coincide with their non-Chinese neighbors).
While UTC is commonly used, it is not the only way to express time in the US Military. For Naval messages, Date Time Group (DTG) is used in place of UTC. The format for DTG is: DD TTTT Z MMM YYYY. Let’s plug 1000 UTC + 0 on December 25, 2018 to this format: 25 1000 Z DEC 2018. For Naval messages, as with many military messages, Zulu is the standard time used. The “Z” in the above message confirms that the time is in Zulu. To convert Zulu time to local time, use the same rule as in UTC conversions. If I want to convert 1000 Z to New York time, I would write 0500 R, with R denoting the time zone in which New York sits. Messages are sent with the standard Zulu time to reduce errors in understanding when a message was sent or when an order needs to be executed. In this format, conversions, like the above from Zulu to Romeo, are easily done and the number of time-related errors are significantly reduced.
Nautical Time Zones
Even with advancements in GPS, longitude and latitude are still key aspects of charting and navigation on ships. Longitudinal lines are evenly spaced every 15 degrees along the Earth’s meridian. Zero degrees longitude is located at Greenwich, England, following the same standard as UTC. Every 15 degrees longitude is roughly equivalent to one hour of time change. For example, UTC + 1, or Alpha, is 15 degrees longitude. UTC -1, or November, is -15 degrees longitude. At the International Date Line, Mike and Yankee are split at the 7.5-degree mark to provide clarification as to which side of the Date Line a ship resides.
A ship adopts local time whenever she is within a country’s territorial waters (within 12 nautical miles of land). At sea, ships are able to transition one hour for every 15 degrees longitude but some opt not to do so in order to maintain a steady schedule for the crew. So even with clearly defined time zones, many opt not to follow them perfectly.
International Date Line
The International Date Line, also known as the Prime Meridian, sits at 180 degrees Longitude and runs from the north pole to the south pole. There are two commonly used iterations of the Date Line: the De Jure Date Line and the De Facto Date Line.
The De Jure Date Line is commonly referred to as the Nautical Date Line and was established by the Anglo-French Conference on Time-keeping at Sea in 1917. The Nautical Date Line follows the 180 degree meridian except for when it overlaps with territorial waters, which is within 12 nautical miles of land. While not often, some ships end up crossing the Date Line twice on one trip: once, say, as they pass the 180 degree meridian to the west, back if they dock at a local country that considers itself east of the Date Line, and then again when they leave the country’s territorial waters.
The De Facto Date Line is nation specific and therefore does not extend into international waters (where the De Jure Date Line takes effect). Each country has the right to establish in which time zone they reside even if it does not perfectly fit within longitudinal degrees. This was done partially so that countries that reside along the date line can ensure they reside one side of the line. As demonstrated in the diagram below, the De Facto Date Line is not a perfect line and continues to allow for changes as territories change hands.
A recent example of a county transitioning from one “side” of the Date Line to the other occurred on Kwajalein in 1993. Kwajalein is the largest of the Marshall Islands and sits, geographically, west of the Date Line. However, the United States Army established a missile test range on Kwajalein after World War Two and therefore kept time as if they were east of the Date Line (using the same time zone as Hawaii). Decades later the Kwajalein government requested to be moved back to the west of the Date Line, which meant losing a day in the hop from east to west. Kwajalein, therefore, removed Saturday, August 21, 1993, from its calendar (which seems akin to leap day for anyone celebrating August 21st as a birthday) and began keeping time with the rest of the Marshall Islands. However, Kwajalein was still working substantially with Hawaii and since the residents were now a day ahead of Hawaii, they moved their work week from Monday through Friday to Tuesday through Saturday.
Time Zones have always played an important role in peoples’ lives, including before their official invention. Even religious leaders had to navigate start times for holidays and for the Sabbath based on when the sunset in different locations. Telling time has come a long way from solar time via a sundial, which often different up to 15 minutes due to the elliptical shape of the Earth.
Although countries today have regulated their local time zones, change will continue to take place. As territories change hands, their local time zones may change. Some countries, like China, may one day adopt their unofficial time zones and establish more than one official zone. Even at sea, Sailors do not always follow time changes as they move past degrees of longitude. Time zones may not be perfectly divided and may continue to change but at least we now know exactly what time the train is supposed to arrive.