Anthony Gray Clock Repair and Restoration

Hamilton Marine Chronometer Model 21

World War II Hamilton Model 21 Two Day Marine Chronometer in original mahogany case.

This good example of Hamilton’s justifiably famous marine chronometer is a specialized timekeeper for determining longitude at sea. It is serial no. 2040 from a run of approximately 10,000 similar timekeepers made by Hamilton Watch Co, Lancaster, PA in 1942.

Price band B


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., including the famous ovalising balance.

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.

So here is a chance to purchase this fine instrument in good working order with an early serial number. Complete with its outer wooden carrying case. If I was going to sea with a chronometer, this is the model I would take with me over all others.

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