In 1966, Hamilton acquired the Buren Watch Company in Switzerland, including all factories and technologies that had been developed by Buren up to that point. From 1966 to 1969, Hamilton Lancaster and Buren Switzerland were operated as a joint concern, with Hamilton using a number of Swiss movements for their "American" watches and Buren utilizing a number of components manufactured by Hamilton Lancaster. It was during this time that Hamilton started to selectively incorporate the highly innovative Buren Microtor (a.k.a. Micro Rotor/Microrotor) movement into small numbers of certain upper tier watches, in addition to their ordinary hand-wind and traditional automatic watches.
The Buren (now Hamilton/Buren) Microtor was the first patented automatic wristwatch movement to eliminate the sizable external oscillating weight inherent to most automatic winding watches. Instead, it utilized a much smaller weight that was entirely integrated into the chassis of the movement. This design allowed for a substantially slimmer automatic watch that still retained a center sweep second hand. The Microtor concept was also conceived by Universal Geneve for use in their famous Polerouter series of timepieces during this same time. The official title of "first Microtor movement" is still in dispute amongst some horology aficionados, even though Buren patented their design in 1954 while Universal Geneve applied for their patent in May 1955.
In 1969, the Hamilton Watch Company completely ceased its American manufacturing operations with the closure of its factory in Lancaster, Pennsylvania, shifting the entire balance of its manufacturing operations to the Buren factory in Switzerland.
From 1969 to 1972, all new Hamilton watches were produced in Switzerland by Hamilton's Buren subsidiary. In 1971, the Buren brand was returned to Swiss ownership and by 1972, the Buren-Hamilton partnership was dissolved and the factory liquidated, due to decreased interest and sales of the Hamilton-Buren product.
Founded 1873 in Büren, a medieval little town at the river Aare in Switzerland, by Fritz Suter-Antenen. Suter-Antenen produced pocket watches, first with cilinder escapement, after 1885 with Anker escapement, winding with key.
1898 H. Williamson Ltd. London bought the label and the factory, increasing the production of pocket watches in many calibres, all manufactured completely inhouse. From 1916 to 1923 a kind of interchangeable parts for the different calibres were developed. In 1925 a patent for the stones used as bearings was granted, these stones being pressed into their place, as applied today in every watch.
Between 1925 and 1930 a broad set of pocket and wrist watches was developed (calibres 373, 25, 335, 385, 375, 378, 875, 415, 400 tonneau, 975, 460, 461, 462, 293 and 70). Annual production in Büren was about 200'000 time-pieces.
The crisis after 1929 forced Williamson Ltd. to sell the facilities in Büren to a local group of new shareholders and the swiss-american financier Roland Gsell.
From 1932 onwards the „Buren Watch Company S.A.“ developed rapidly new wrist watch calibres ( no. 40, 45, 35, 60, 295, 350, 50, 356, 14, 370, 410, 380, 462, 30 and 565). Buren participated in the race to ever flatter watches, e.g. by the calibre 300, 280 (very flat with 2,8 mm, and acclaimed as very precise, in 1960), and cal. 65 for flat women watches. All parts were still manufactured inhouse. 1945/6 the fabrication of cal. 525 was started, an automatic bumper movement watch, in 1953 the automatic calibres 535-539 with „Rotowind“(with second hand from center, or power reserve indication).
1954 Buren established the patent for its Minirotor – the small rotor integrated at the same level as the rest of the movement, which can thus get very flat. The watch was called „Superslender“ (calibres 1000 and 1001 and produced from 1957 onwards), then adapted to „Intramatic“(cal. 1280, 1281, 1320 and 1321) and „Slendermatic“for women. The patent for Superslender was licensed – together with Universal of Geneva to other firms, eg. Complication-Piaget or IWC, the patent for Intramatic was licensed to Baume & Mercier, Bulova and Hamilton (used in the "Thin-O-Matic" line).
The automatic mouvements were further developed, together with Breitling, Heuer-Leonidas and Dubois Depraz, to build the world‘s first automatic chronograph in 1969 (cal. 11 „Chronomatic“), where the crown (seldom to use in an automatic watch) was set at the left of the dial, the two chronograph push-pieces at the right side. In 1966 the swiss-american owner Gsell wanted to retire and engineered the aquisition of Buren by the Hamilton Watch Company (USA). Hamilton transferred its production 1969 to Büren, doubling its capacity to about half a million pieces. But the markets for Buren-Hamilton watches suddenly shrank, 1972 the factory was liquidated.