The first Gruen wristwatches were introduced in 1908. These found favor with women buyers, but were not popular with men at the time (who considered wristwatches feminine). The company did not return to making wristwatches for men until World War I, when military use made wristwatches acceptable for men to wear.

In 1917 the company moved to a newly-constructed building named Time Hill, in Cincinnati. The building, which still exists, was designed to look like a medieval guild hall.

In 1922 a consolidation took place where the D. Gruen, Sons & Co, Cincinnati, The Gruen Watch Manufacturing Co, Biel/Bienne and the Gruen National Watch Case Co, were merged into “The Gruen Watch Company”.

In marketing and advertising, the Gruen Watch Company used 1876, and later, 1874, as its official founding date. By the mid-twenties, Gruen’s sales had reached over five million dollars. In total sales, it had become the largest watch company in the U.S., as well as first in the average watch price!

In 1935, Gruen introduced the first “Curvex” wristwatches for men. The Curvex is the company's most famous design. Expanding on the then-current fashion for long, rectangular wristwatch shapes, the Curvex watches were curved to wrap around the wearer's wrist.

The biggest innovation of the design was to place a curved movement inside the curved case, allowing the watch to be thinner and more curved, and allowing the movement to be larger, more durable and more accurate than would have been possible if a smaller, flat movement was used. A year later, Curvex models for women were introduced.

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 WWII, some watches were still manufactured at the Precision Factory in Switzerland and imported.

It was during and shortly after WWII 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.

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