American metal chronometer model 21BC Circa 1942

Marine chronometer in original brass case
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A marine chronometer, probably the rarest American chronometer with a “sidereal break circuit”, made by the Hamilton Watch Company in Lancaster Pennsylvania, United States of America, circa 1941. This watch features a non magnetic screwed metal (heavy cast brass) case with electrical contact device and the original labelling. The silvered brass dial features an outer minute and hour track with Arabic hour numerals, a subsidiary seconds dial at 6 o’clock, a 48 hour power reserve indicator at 12 o’clock, blued steel time hands, a fine, needle like straight baton seconds hand and a very small, simplified leaf or lance shaped pointer hand that moves across the 0 to 48 hour power reserve scale to indicate the remaining mainspring tension. The numbered movement is equipped with a Hamilton chronometer movement with a spring detent escapement and 14 jewels.
The case and movement have matching numbers and the dial and movement are signed.
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Diameter: 101,6 mm
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Weight: 1.800 – 2.300 gr. (movement & brass bowl alone)
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Signed: Hamilton Lancaster PA U.S.A
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The item presented here is the only Hamilton 21BC chronometer known of with the original case and the US Army marking. “Break Circuit” chronometers were used for a variety of purposes. They provided main signals to control slave clocks on some ocean liners and warships, but were also used in spy planes, among other things. The original case of this item is indicative of such usage.
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Hamilton Watch Company
The Hamilton Watch Company was founded in 1892 in Lancaster, Pennsylvania.

Key individuals involved in its founding and early leadership include: Henry J. Cain: A central figure and major investor who served as the superintendent of the Aurora Watch Company before the merger. He designed the first Hamilton movement, the Grade No. 936, which launched the brand’s reputation for railroad accuracy. Charles D. Rood: An investor from the Aurora group who became the company’s first president in 1894. J.W.B. Bausman: Elected as the initial president of the new company upon its organisation in 1892. Abram Bitner: While he founded the Keystone Standard Watch Co. (Hamilton’s immediate predecessor) in 1886, his company’s bankruptcy led to the formation of Hamilton by the new investor group.

Origin of the Name
The company was named after Andrew Hamilton (and his son James), the original owners of the land in Lancaster, Pennsylvania, where the factory was built. Andrew Hamilton was the Scottish born attorney famous for laying out the city of Lancaster. 

For over a century, it was a titan of American industrial watchmaking, particularly renowned for producing high precision pocket watches that became the gold standard for safety and timing

Military & Aviation Heritage (1914–1945)

The company’s reputation for precision led to extensive partnerships with the U.S. government and military.

• World War I: Hamilton became the official supplier to the American Expeditionary Forces in 1914. During this era, the company began transitioning from pocket watches to wristwatches for soldiers in the trenches, utilising its high quality 0 sized movements.
• Aviation: In 1918, Hamilton accompanied the first U.S. Airmail service between Washington, D.C., and New York. Its watches were also used by pioneers like Admiral Richard E. Byrd during his 1926 flight over the North Pole.
• World War II: In 1942, Hamilton halted all consumer production to focus entirely on the war effort. It produced over one million timepieces, including specialised marine chronometers (Models 21 and 22) that were vital for naval navigation.