The Gruen Watch Company was formerly one of the largest watch manufacturers in the United States. It was in business from about 1894 to 1958 and was based in Cincinnati, Ohio. It was founded in 1908 by German-born watchmaker Dietrich Grün, who changed the spelling of his name to "Gruen" because the letter ü does not exist in English.
During World War II, the Time Hill factory stopped making watches and instead worked exclusively for the U.S. military, manufacturing gauges and instruments for aircraft, ships and submarines. The company also made precision gauges used for delicate surgical instruments and for radios and other electronic equipment. During World War II, some watches were still manufactured at the Precision Factory in Switzerland and imported.
It was during and shortly after World War II that many American watch companies began to lose market share to Swiss imports. Many American watch companies began to move manufacturing to Switzerland in the 1940s and 1950s, while Gruen, who had always manufactured watch movements in Germany or Switzerland, launched the '21' series of wristwatches (named for their 21-jewel movements) which were entirely made in the United States.
The Gruen family sold their interest in the company in 1953, and the firm was broken up and sold in 1958. The watch manufacturing business was moved to New York under new ownership, and manufacturing was done exclusively in Switzerland.
The operation in Biel/Bienne closed its doors in 1977; their wonderful building topping the city was bought by their old supplier, J. Aegler, now Rolex Manufacture.