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Ironhorse Timepieces — From the Workshop
By the Ironhorse Workshop
We have written before about the Hamilton 4992B GCT, the Master Navigation Watch that guided Allied aircrews over Europe and the Pacific during World War II. We thought we knew its full story. We were wrong by about 140 million miles.
Previously in the Ironhorse Workshop: The Watch That Navigated World War II: Hamilton's 4992B GCT and the Race to Keep Time at War
In the summer of 2003, a planetary scientist named Jeff Moersch was looking for a gift. His colleague Steven Squyres was the Science Payload Principal Investigator for NASA's Mars Exploration Rover mission, and the twin rovers Spirit and Opportunity were weeks away from beginning their journey to the surface of Mars. Moersch had an idea: a mechanical pocket watch, modified to keep time not on Earth, but on Mars. He went looking for a watchmaker who could do it. Every one he found told him it could not be done.
The problem is time itself. A Martian day, which NASA calls a sol, lasts 24 hours, 39 minutes, and 35.244 seconds. That extra 39 minutes and 35 seconds is not an approximation or a rounding quirk. It is the precise difference between the rotational period of Mars and that of Earth, and it creates one of the strangest operational realities in modern science. For the first 90 sols of every rover mission, the entire JPL operations team lives on Mars time. Every morning their alarm sounds 39 minutes later than the day before. Within two weeks they are eating breakfast at midnight. Within a month they are driving home from work as their neighbours are leaving for it. A watch that runs on Earth time is, for these scientists, useless for the most important hours of their working day.
Steve Maddox, a professional watchmaker and President of NAWCC Chapter 62 in North Little Rock, Arkansas, read Moersch's posting on a watchmakers' forum and asked a different question than everyone else had. He did not ask whether the modification was possible. He asked how large the difference actually was. When Moersch told him it was approximately 40 minutes per day, Maddox knew immediately that he could solve it, and he offered to do the work for free.
The watch they chose was a Hamilton 4992B GCT. The reasoning was elegant. The 4992B already carried a 24-hour dial, precisely because its original military purpose required navigators to track a full day's arc without ambiguity between morning and evening hours. A Mars sol, at just over 24 hours, fit that same dial with remarkable naturalness. The 24-hour format that had guided B-17 navigators over Germany was the same format that would track a Martian day over the Gale Crater.
Maddox's solution was a masterpiece of applied watchmaking. A standard mechanical escapement beats at 18,000 times per hour, or 300 beats per minute. The rate of a watch is governed by two things working together: the moment of inertia of the balance wheel and the tension of the balance spring. By adjusting the 14 to 20 balance screws around the perimeter of the balance wheel, a skilled watchmaker can alter the beat rate without touching any of the gearing. Maddox calculated precisely how many beats per hour would produce a daily lag of exactly 39 minutes and 35.2 seconds. The answer was 17,518.4 beats per hour. A few hours' careful work with a watchmaker's timing machine, and the 4992B was keeping Mars time to within 2 seconds per day. The same movement that Hamilton built to synchronize with a Greenwich observatory signal in 1944 was now synchronized with the rotation of another planet.
Moersch presented the watch to Squyres in the early autumn of 2003, just as Spirit and Opportunity were closing in on Mars. Squyres put it on a sturdy chain and carried it in his pocket every day for more than two years. Years later, when the watch needed service and he could not reach Maddox, Squyres posted on the NAWCC watchmakers' forum asking for help. "It is my most prized possession," he wrote, from his email address at Cornell University. The lead scientist of one of the most successful planetary exploration missions in history, describing a modified WWII pocket watch as the object he treasured above all others.
The story has a bittersweet postscript. When the MER engineering team went looking for a watchmaker to produce Mars-time wristwatches for the broader mission crew, they did not find Maddox. A watchmaker named Garo Anserlian in Montrose, California arrived at the same solution independently and produced the wristwatches that eventually spread across JPL. Maddox, who had solved the problem first, for free, out of genuine curiosity, was not part of that chapter. It is the kind of quiet injustice that horology seems to collect.
What the story of the Mars 4992B adds to everything we have written about this watch is a kind of completeness. We described the 4992B as representing the full arc of the American precision timekeeping tradition: the same demand for accuracy that drove the railroads after Kipton, pressed into the service of a world at war. That arc, it turns out, did not end in 1945, or 1970 when Hamilton ceased production. It continued, in a watchmaker's workshop in Arkansas in the summer of 2003, when a man turned a balance screw by a fraction of a degree and made a 60-year-old instrument keep time on a world it was never built to reach.
At Ironhorse, the 4992B we are currently restoring carries a 1944 serial number. It flew, or sailed, or rode in someone's pocket through a war. It has since kept Earth time for eighty years.
We find ourselves thinking, after researching this story, that it has earned a rather extraordinary legacy to live up to.
Filed under: Hamilton · 4992B · Military · NASA · Mars · Horology · WWII
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