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Hamilton No. 1 Box Chronometer

Hamilton No. 1 Box Chronometer

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This instrument is a specialized timekeeper for determining longitude at sea. It is serial no. 1 from a run of approximately 10,000 similar timekeepers made by Hamilton Watch Co, Lancaster, PA in 1942.
World War II created a dire chronometer shortage for the United States. Before the war, most chronometers for American military and civilian customers were imported. Only a few American firms—including William Bond & Son of Boston and the New York establishments of John Bliss Inc. and T.S. and J. D. Negus—finished chronometers from parts imported from European makers. Chronometer making was a craft, with only a few hundred produced in any given year. When the war started in 1941, European suppliers of parts and finished instruments halted exports to the United States.
Anticipating the arrival of war, the U.S. Naval Observatory had asked American domestic watch manufacturers in 1939 for their participation in mass-producing chronometers. Domestic watch manufacturers Hamilton and Elgin agreed to undertake the design and production, but only Hamilton’s product met Navy accuracy requirements. Hamilton delivered two prototypes to the Navy on 27 February 1942, which passed with an error rate of 1.55 seconds per day. The firm went on during the war to mass-produce 8900 more chronometers for the Navy, 1500 for merchant shipping and 500 for the Army. Between 1942 and 1944, the price dropped from $625 to $390 per timekeeper.
Hamilton’s design for its Model 21 chronometer did not copy traditional European standards. Instead the design introduced key changes to improve accuracy. The modifications included changes to the escapement and the chronometer’s oscillating unit—the balance and hairspring assembly.
To find longitude at sea, a chronometer would be set to the time of a place of known longitude, like Greenwich, England, the prime meridian. That time, carried to a remote location, could be compared to local time. Because one hour of difference in time equals 15 degrees difference in longitude, the difference in time between the chronometer and local time would yield local longitude.
1. Dick, Steven J. Sky and Ocean Joined: The U. S. Naval Observatory 1830-2000. Cambridge: Cambridge University Press, 2003.
2. Whitney, Marvin. The Ship’s Chronometer. Cincinnati: American Watchmakers Institute Press, 1985.
Object Name
box chronometer
date made
place made
United States: Pennsylvania, Lancaster
Physical Description
brass (overall material)
steel (overall material)
glass (overall material)
wood (overall material)
overall - chronometer case: 7 1/2 in x 8 in x 7 3/4 in; 19.05 cm x 20.32 cm x 19.685 cm
overall - carrying case: 9 1/2 in x 12 in x 10 in; 24.13 cm x 30.48 cm x 25.4 cm
overall - from catalog card: 7 1/2 in x 7 1/2 in x 7 1/2 in; 19.05 cm x 19.05 cm x 19.05 cm
ID Number
catalog number
accession number
Credit Line
Department of the Navy. Bureau of Ships
See more items in
Work and Industry: Mechanisms
Measuring & Mapping
Time and Navigation
Time and Navigation, National Air and Space Museum
Data Source
National Museum of American History
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I have a couple of these magnificent Hamilton Marine Chronometers and both are all original, with matching serial numbers on the caseback, the bezel and the movement; all original in the boxes with original glass and straps. One of them is a 4 digit serial number, 42XX. The other is 71XX. Both are in fantastic condition and run true. They hold pride of place among my small collection of clocks, as I’m a more avid watch collector. But I couldn’t pass on either of these beauties. Referring to the above post where someone is trying to locate where his chronometer might have been assigned, the NAWCC has tremendous resources and if he or she can find a clock repair specialist, they can be invaluable in locating information, especially if all serial numbers match meaning it wasn’t repaired by cannibalizing other chronometers to replace parts. Specifically the bezel or caseback. My clock specialist had a friend who worked at the Navy Annex in Arlington, and using the 4 digit serial number, he was able to locate the entire file concerning my Model 21. From the Hamilton delivery invoice,along with the chronometer certification results, the entire instruction manual, the maintenance manual and the signature of the receiving officer. He was a Lt.jg.but his signature is illegible. Further searching turned up the paperwork where it was decommissioned and declassified, with a signature by a different Lt.jg. And countersigned by another, which allowed them to be sold to the public. The gentleman who did all the Successful research Also was kind enough to make copies of every piece of paper relating to my chronometer, including the instructional manual and the maintenance manual, which includes how they verified chronometer status using the vacuum chambers and temperature regulators…I.e. special refrigerators. The packet he gave me also included copies of the invoice and the signed, countersigned, stamped, and the Naval seal across them, making it all cleared and legal for a civilian to own. There’s well over 100 pages in the packet with the manuals taking up most of those pages. I’m not sure how and I didn’t ask, but I have an original of the decommissioning and declassified document with the officers’ signatures. He probably wouldn’t have told me, anyway. It matters not, because the provenance of this particular Model 21 makes it one of the rarest Hamilton Naval Marine Chronometer Model 21 that has every piece of paperwork intact and with the chronometer that isn’t in a museum. The man I bought it from was bemused when I asked if I could unscrew the bezel and back to check the serial numbers; he didn’t know they were there. He took my first offer, $645. I’d have gone much higher, but he said he just wanted to be rid of it because his wife hated it as it didn’t match her meticulously decorated den. So be it. I ended up with a fantastic, well maintained WWII ship’s master chronometer and I’ve been enthralled since I first saw it was original. Please pardon this lengthy post. I’m blind and quote everything which then gets printed. When talking, I think most people will say much more than if they were typing. I am looking for a Hamilton Model 22 Deck Watch in great shape and with the box. It would be a nice complement to my Model 21 Master Chronometer. Thank you for your time and patience. And I hope the above poster locates the information of which he’s looking.
I recently purchased a chronometer similar to the pictured example along with hardwood/leather strapped carrying case. It has a tag screwed onto the instrument indicating it was used during WWII. If I locate the serial# would it be possible to identify what vessel or vessels it served? There is also a painted ID # on the carrying box. Thank you.
If the chronometer is made by Hamilton, with the serial number you might be able to determine who purchased it and when. There are Hamilton marine chronometer log books in the library of the National Association of Watch and Clock Collectors in Columbia, Pa. Once the purchaser is known, to find the specific vessel(s) will take additional research.

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