Zulu Time

Oct. 1, 1991

Throughout the Persian Gulf War, television reporters kept telling US viewers what time it was locally in Saudi Arabia. They did that so their audience wouldn’t get confused about who was doing what to whom, when. The whole thing would have been easier if everybody simply had used Greenwich Mean Time or, in military parlance, “Zulu Time.”

That international time system was created precisely to solve such problems. As Zulu Time evolved, the world also acquired a better navigation system, a more reliable timepiece, and far more sensible railroad timetables.

Before all that could happen, somebody first had to break the natural day into identifiable parts. For that, we may well have to thank the forebears of today’s Iraqis. While the rest of the world was still counting on fingers and doing base-ten arithmetic, the ancient Mesopotamians fell in love with the number sixty–no one knows why–and used it to divide all sorts of things. By the time Mesopotamia became Iraq, the world was stuck with the twelve-month year (one-fifth of sixty), the twenty-four-hour day, the sixty-minute hour, the sixty-second minute, and the rest of it. Once you had the numbers, you could keep time with a sundial, an hourglass, a pendulum, any number of things. If you needed to be precise, you could check your local observatory. That worked fine for several centuries. Then another problem came up.

People emerged from the Middle Ages with a more powerful yen to travel and took to the sea in large numbers. For a while, they just wandered around, not caring too much when they got home, but before long ships were hauling goods between the continents. As this import-export business grew more competitive, traders needed to know more than just which way was home. They had to know where they were at any given time and how to get where they were going by the shortest route.

European astronomers worked out a navigation system. In 1675, King Charles II built a major new observatory at Greenwich, England, and set it to turning out star charts. With enough of those charts, a navigator could find his longitude and latitude any place in the world and keep to a precise course. All he needed was a sextant and a good clock.

What Was Missing

The bad news was that, though the Europeans had plenty of sextants, nobody had yet invented a really accurate timepiece. Ships still were getting lost at sea, sometimes permanently. By 1714, things were so bad that the British government offered a reward of £20,000 sterling to anyone who could produce a state-of-the-art, reasonably accurate timepiece.

A mechanic named John Harrison came up with a chronometer that, after making a trip to Jamaica, was found to be “off” by a mere five seconds. The British government accepted it. Modern maritime navigation was off and running.

With one thing and another, however, it took Harrison forty years to collect his prize money, and it wasn’t long afterward that world travelers faced another problem that the best of watches couldn’t solve.

In the early 1830s, steam-driven trains were introduced in Britain and the United States. Soon goods and people were moving around faster than ever before, and the railroads were knitting together hundreds, perhaps thousands, of villages.

The hitch was that all of these burgs and hamlets kept their own time. An 1841 timetable for Britain’s Great Western Railroad told bewildered passengers the following: “London time is kept at all stations, which is about four minutes earlier than Reading time, five and one-half minutes before Steventon time, seven and one-half minutes before Cirencester time, and fourteen minutes before Bridgewater time.”

As the railroads expanded, things got worse. By 1880, railroad companies around the world had laid more than 150,000 miles of track. Railroads in the United States alone were dealing with more than 100 separate time schemes. In 1883, Canadian and US railroad companies worked out a system to relieve the situation. One year later, the plan was adopted by an international conference.

The plan divided the Earth into twenty-four time zones, demarcated by meridians fifteen degrees apart. France wanted Paris to be the starting line. The Americans promoted Washington. However, because Britain still ruled the waves, and much else besides, the time-organizers finally agreed to run the Prime Meridian through the old observatory at Greenwich.

Standard Time Gets Airborne

By the time the Wright brothers took to the air, standard time was used in most of the civilized world. The Wrights’ first flights were too short to make full use of the system. Twenty years later, however, two Army Douglas World Cruisers circled the Earth, and global aviation was in business. The value of the standard time system became apparent.

As aviation shrank the globe, accurate navigation became even more vital. Over land, pilots could follow highways and railroad tracks; by the mid-1920s, they even had a system of lighted airways and radio beacons. However, flying in bad weather and over water was quite another story. Most pilots weren’t trained to cope.

Early in the 1930s, the US Army Air Corps created a unit at Bolling Field near Washington, D. C., to study the problem. It hired Harold Gatty, a navigator just back from a worldwide flight, as an advisor. Most of the needed tools were at hand. The Germans had developed an aerial sextant. Accurate drift meters had appeared soon afterward, along with slide rules for solving course and distance problems. The mariners’ star charts had been adapted to aerial almanacs. The Army had watches as accurate as the big shipboard chronometers. The trick was to teach flyers to use the stuff.

The Air Corps set up a navigation training program for pilots and later expanded it into a full five-month course for navigators. At the heart of the new air training was a centuries- old technique. It amounted to drawing a scale model of the plane’s course and airspeed and adding a line to represent wind speed “and direction. From that, the navigator could figure his heading, ground speed, and time of arrival. Originally it was called “deduced reckoning,” but the first word was abbreviated to “ded,” and the phonetic pronunciation “dead reckoning ” became the accepted term.

The process involved taking repeated position readings using everything from maps to celestial observation. Celestial fixes were made using star charts based on Greenwich Mean Time. The Army Air Forces adopted it not only for navigation but also for timing its worldwide operations. World War II navigators lived by it. Their premission “time hacks” took on the solemnity of religious rituals, and GMT bound the faithful together like some secret password. Army Air Forces navigators from Italy to the Far East could tell you to the second what time it was in that little town near London.

Since the war, technology has taken much of the drudgery out of navigation, and in many aircraft, black boxes have replaced human navigators altogether. Some systems even take their celestial “fixes” from man-made satellites rather than from the stars.

Time systems themselves have gone through a series of changes. Until well into this century, Greenwich Mean Day began at noon because astronomers didn’t want to change dates during their overnight vigils. That practice confused other people, but it was not until the 1920s that the schedule was revised. The stargazers still kept their system but renamed it Greenwich Mean Astronomical Time. The rest of us went on a midnight-to-midnight routine. Officially it is “Universal Time,” but most people continue to call it GMT or use the local British equivalent, “Greenwich Civil Time.”

Zero, Zebra, Zulu

As is typical of the military, it coined its own term. Since Greenwich is the site of the “zero meridian,” they called GMT “Zero Time” or simply “Z- Time.” In the phonetic alphabet that the flyers of the time used to make themselves understood on their radios, “Z” became “Zebra.” When the alphabet was changed, the call sign became “Zulu.”

Zulu Time no longer emanates from Charles II’s old observatory. In 1958, the Greenwich astronomers moved to the English coast to escape London’s fog and city lights. They still correct their observations to show the time at the Greenwich meridian, but the old building there has been converted to a museum.

Nor are the 1884 time zones still the neat parallel lines we envision. They wiggle around international borders and state boundaries and are redrawn every now and then. When US time lines were changed in 1963, they moved several west Texas towns into the Central Time Zone, where they are an hour ahead of parts of New Mexico that are farther east. In some countries, the time zones are based on half-hour differences from GMT. A few nations have not adopted standard time.

Some scientists and chronologists would like to dump the old, Mesopotamian system of keeping time and come out with metric clocks. Some firebrands proposed that change during the French Revolution, when the populace was trying to get rid of everything aristocratic, including the timepieces. They didn’t succeed. Later drives didn’t get any further.

Some sociologists think we already may have gone too far just by introducing digital clocks. If they take over completely, whole generations could grow up without ever seeing an analog clock face. They wouldn’t know what the gunner in an old war movie was talking about when he said, “Bandits at ten o’clock high!”

We’re probably in no immediate danger of going metric or all-digital, but there have been many subtler changes in the basic units of time. For centuries, for example, the second was the smallest division of the solar day. Then scientists discovered that electrical currents make quartz crystals oscillate at regular rates. Now atomic clocks use the natural resonance of cesium atoms to divide time even more finely, cutting it into millionths and billionths of a second.

Wait until somebody comes out with a powerplant able to kick a spacecraft along at close to the speed of light. At that speed, Albert Einstein maintained and subsequent experiments confirmed, your atomic Timex should slow to a crawl and your biological clock along with it. If Einstein was right, you could come back from a lengthy trip into the cosmos to find yourself younger than your grandchildren.

Chances are, if that happens, some operations type will be hanging around to make sure you close out your log on Zulu Time.

Bruce D. Callander is a regular contributor to AIR FORCE Magazine. Between tours of active duty during World War II and the Korean War, he earned a B.A. in journalism at the University of Michigan. In 1952, he joined Air Force Times, becoming editor in 1972. His most recent article for AIR FORCE Magazine, “The Sartorial Splendor of the Air Force That Was,” appeared in the June 1991 issue.